Abstract:
A scanner configured to provide a two-dimensional scan of a radiation beam moving along the path, including two deflectors and a scan lens located downstream in the path of the beam from the deflectors and separated from the farthest deflector by air equivalent distance at least equal to the focal length of the scan lens.

Description:
This invention relates generally to a scanner system for providing a two-dimensional scan of a radiation beam, for example, from a laser. 
     More particularly, it relates to scan lenses or scan lens systems used in pre-objective optical scanning systems for focusing a beam of radiation being deflected by scanned deflectors. 
     Most pre-objective optical scanning systems use a laser and single scanner to provide spot motion in the &#34;fast scan&#34; or &#34;line&#34; direction. The positioning of the spot in the &#34;slow scan&#34; or &#34;page&#34; direction is controlled by motion of the recording material. For example, this method is generally employed in laser printers. 
     A pre-objective laser scanning system (i.e. an optical scanning system employing a laser in which deflectors are located in front of a scan lens) employing two scanning deflectors, which control the deviation of the beam in orthogonal directions, allows the recording material to remain motionless during the recording process. We recognized that this allows a simpler transport mechanism for the recording material, such as paper or film, because the transport mechanism is only required to move the recording material into position before the recording begins and to remove it after the recording is finished. Thus, the image quality written onto such recording material in a dual deflector scanning system is no longer affected by the precision of the page direction recording material transport mechanism. We also recognized that this is an especially important advantage for small format recording materials, such as microfilm or microfiche, because the need for a film transport mechanism which will accurately position the film to tolerances of less than 1 μm is eliminated. 
     U.S. Pat. No. 4,714,960 discloses an optical scanner system with more than one light path or more than one deflection. This scanner was designed to be &#34;television compatible&#34; and utilized a polygon scanner and an afocal lens system for imaging on a detector array. Neither requirements imposed by such an optical scanner system on the scanning lens system, nor the configuration of a scanning lens system were disclosed. 
     U.S. Pat. No. 4,736,110 discloses a dual deflector image pick-up apparatus. The configuration of the scan lens is also not disclosed. 
     Finally, U.S. Pat. No. 4,714,830 describes a light beam positioner having dual deflectors. Again, there is no disclosure of the objective (or scan) lens. 
     We found that using this two-deflector scheme introduces new and unusual requirements onto the scan lens. The use of two scanning deflectors in front of the scan lens means that the first deflector is now located at a greater distance from the scan lens than has been customary in prior art. The aberrations of the scan lens must be corrected for a scanning deflector located at a great distance from the lens. It has long been recognized that the design of scan lenses for use in pre-objective single detection scanning systems is greatly complicated when the scanner is located at large distances from the scan lens, because the location of the scanning deflector defines the entrance pupil for the scan lens. For example, Hopkins and Buzawa state that &#34;A lens optimized for an entrance pupil located at the scanning element has quite a different form compared to a normal lens with an internal aperture stop. Unfortunately, this requirement tends to increase the complexity and size so every effort should be made to minimize the distance between the lens and the scanner&#34; (R. E. Hopkins and M. J. Buzawa, &#34;Optics for Laser Scanning&#34;, Optical Engineering, 15,2,1976, pages 90-114). Prior pre-objective single deflector scanners are limited to arrangements in which the scan lens is located between 15% and 100% of the scan lens focal length behind the deflectors. Lenses of this type are described in U.S. Pat. Nos. 5,087,987; 5,031,979; 4,527,858; and 5,111,325. 
     Our requirement that the first scan lens be located a large distance away is complicated by the fact that the scan lens must be corrected for two deflector positions. Prior art showed no such lenses and disclosed no pre-objective scanning system employing such a scan lens. 
     Finally, it was discovered that a line bow problem, typically present with a single, pre-objective scanner, is more difficult to correct in a dual scanner system. 
     The problems of line bow in holographic scanners incorporating one deflector are discussed in the article entitled &#34;Holographic Scanners, Applications, Performance and Design&#34; by Glen T. Spincerbox, in &#34;Laser Beam Scanning&#34; ed. by Gerald F. Marshall, Marcel-Dekker, New York, 1985, pgs. 41-45. B. Narayan, in U.S. Pat. No. 4,904,034 describes a method to minimize the line bow produced by a pre-objective scanner using a single holographic scanning system. However, no prior art is known concerning line bow correction when a holographic grating is used as the line direction deflector in a dual deflector pre-objective scanner system. 
     It is an object of the present invention to produce an improved pre-objective scanner. 
     According to the present invention, a scanner configured to provide a two-dimensional scan of a radiation beam moving along a path includes: (1) a first deflector for deflecting the beam through a first scan direction at a first angular velocity; (2) a second deflector for deflecting the beam through a second scan direction at a second angular velocity substantially orthogonal to the first scan direction; and (3) a scan lens located downstream in the path of the beam from the deflectors for focusing the beam to a spot on a surface, the scan lens having appropriate distortion characteristics to insure that a linear velocity of the spot on the surface is proportionate to the angular velocity of both said deflectors. 
     It is also an object of the present invention to produce an improved objective lens (or scan lens) for an optical scanning system. 
     It is yet another object of the present invention to produce an objective lens (i.e. a scan lens) for an optical scanning system which is corrected for two deflector positions or two stop locations. 
     As stated above, we discovered that a scan lens used with a dual-deflector pre-objective scanning system must meet special requirements that are not necessary for scan lenses used with a single scanning deflector. These requirements are described below in detail. Scan lenses meeting these conditions are not known. 
     1. In dual-deflector scanner systems, the scan lens aberrations must be well corrected for any combination of rotations by either or both of the two deflectors. Since the deflector position in the pre-objective optical scanning system defines the entrance pupil for the scan lens, this is equivalent to stating that the performance of the scan lens must also be corrected when the stop is shifted between the locations of the two deflectors. Since the chief ray moves transversely as the pupil is shifted longitudinally, the aberrations of the scan lens must be corrected over a larger pupil diameter than the actual diameter of the laser beam entering the scan lens. 
     These objects and requirements can be achieved by a lens (also called a scan lens or a scanning lens) for projecting a beam of radiation moving along an optical path from front to rear, the lens comprising three groups of lens elements in order: (1) a negative group with a front-most lens element concave to the front; (2) a first positive group of lens elements having at least two positive power lens elements and no negative lens elements, the first lens element of the first positive group having its strongest surface facing the rear; and (3) a second positive group of lens elements, the second positive group having stronger optical power than the first positive group, the second positive group including at least one positive meniscus lens component which is concave to the rear. It is preferred that ##EQU1## where efl is the focal length of said scanning lens, efl 1  is the focal length of said first negative lens group, efl 2  is the focal length of said first positive lens group and efl 3  is the focal length of said second positive lens group. 
     According to one of the embodiments of the present invention, the negative group consists of a single lens element satisfying the following condition: 
     
         0.58≦X≦0.65 
    
     where X is the bending of the single lens element. 
     According to another embodiment of the present invention, the negative group comprises a plurality of lens elements and the first lens element of this group meets the following bending condition: 
     
         0.82≦X≦1.02. 
    
     According to a preferred embodiment of the present invention, the first positive group comprises three positive lens elements, the three positive lens elements satisfying the following conditions: 
     
         -1.70≦X&#39;.sub.1 ≦0.94, 
    
     
         -0.46≦X&#39;.sub.2 ≦-0.26, and 
    
     
         -1.98≦X&#39;.sub.3 ≦5.22, 
    
     where X&#39; 1 , X&#39; 2 , and X&#39; 3  represent the bending of the first, second and third consecutive lens elements of the first positive group. 
     According to yet another embodiment of the present invention, the second positive group consists of two lens components and satisfies the following conditions: 
     
         -3.11≦X&#34;.sub.1 ≦-2.56, and 
    
     
         2.05≦X&#34;.sub.2 ≦2.21, 
    
     where X&#34; 1  is the bending of the first lens component of the second positive group and X&#34; 2  is the bending of the second lens component of the second positive group. 
     2. It is another object of the present invention to produce an optical scanning system wherein, the linear scanning velocity on the recording material be proportional to the angular velocity of each of the scanning deflectors. This object requires introducing the correct amount of negative distortion into the design of the scan lens, taking into account the effects of stop shifting on distortion. For the case where the &#34;fast&#34; or &#34;line&#34; scanning is controlled by a rotating holographic gratings, the distortion characteristics of the scan lens must be balanced between the aforementioned need to achieve scan linearity and the need to minimize line bow over the entire range of the &#34;page&#34; or &#34;slow&#34; deflector. 
     As stated above, the aforementioned object of the present invention can be achieved by a scanner configured to provide a two-dimensional scan of a radiation beam moving along a path, comprising: (1) a first deflector for deflecting the beam through a first scan direction at a first angular velocity; (2) a second deflector for deflecting the beam through a second scan direction at a second angular velocity, said second scan direction being substantially orthogonal to said first scan direction; and (3) a scan lens located downstream in the path of the beam from these deflectors for focusing the beam to the spot on a surface, the scan lens having appropriate distortion characteristics to insure that a linear velocity of the spot on the surface is proportionate to said first and second angular velocities. 
     According to a preferred embodiment of the present invention, a scan lens comprises three units of lens elements located in order in the direction of the beam, a first negative power lens unit, a second positive power lens unit and a third positive power lens unit, wherein the second, positive power lens unit is primarily responsible for introducing the distortion characteristics. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a simplified schematic of the side view of the optical scanner system 10 according to the preferred embodiment of the invention; 
     FIG. 2 is a more detailed schematic of the optical scanner system 10 of FIG. 1; 
     FIG. 3 is a side view of the back portion of an optical scanner system 10 shown in FIG. 1; 
     FIG. 4 is a top view of the back portion of the optical scanner system 10 illustrated in FIG. 3; 
     FIG. 5 illustrates the direction of the object plane wave (OPW) and the reference plane wave (RPV) for the holographic grating utilized in the optical scanner system 10; 
     FIG. 6 illustrates the construction and orientation of prism P utilized in the optical scanner system 10; 
     FIG. 7 illustrates a side view of the portion optical scanner system 10 shown in FIG. 3, but at zero holographic grating rotation and maximum galvo rotation; 
     FIG. 8 illustrates a top view of the portion of the optical scanner system 10 illustrated in FIG. 7, but at zero galvo rotation and at maximum holographic grating rotation; 
     FIG. 9 is a schematic of the side view of the first embodiment of the lens system 18 of the scanner system 10; 
     FIG. 10 is the schematic of the side view of the lens system 18a of the second embodiment; 
     FIG. 11 is the schematic of the side view of the lens system 18b of the third embodiment; 
     FIG. 12 is the schematic of the side view of the lens system 18c of the fourth embodiment; 
     FIG. 13 is the schematic of the side view of the lens system 18d of the fifth embodiment; 
     FIG. 14 is the schematiC of the side view of the lens system 18e of the sixth embodiment; 
     FIG. 15 is the schematic of the side view of the lens system 18f of the seventh embodiment; 
     FIG. 16 is the schematic of the side view of the lens system 18g of the eighth embodiment; 
     FIG. 17 is the schematic of the side view of the lens system 18h of the ninth embodiment; 
     FIG. 18 is the schematic of the side view of the lens system 18i of the tenth embodiment; 
     FIG. 19 is the schematic of the side view of the lens system 18j of the eleventh embodiment; 
     FIGS. 20A-H show the effect of the stop shift on the transverse aberration for the first lens embodiment; 
     FIG. 21 shows how the use of two deflectors leads to the pupil size being larger than the actual entering beam; 
     FIG. 22 shows the scan linearity performance of the first preferred embodiment of the present invention; 
     FIG. 23 illustrates line bow characteristics of the first preferred embodiment of the present invention; 
     FIG. 24 shows the OPD correction as a function of holographic grating rotation at a zero galvo mirror orientation; 
     FIG. 25 shows the OPD correction as a function of galvo mirror rotation at zero holographic grating orientation; and 
     FIG. 26 shows the optical performance of the optical system of the first preferred embodiment in the comer of the largest format. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the present invention is not limited to use as a laser printer, the scan lens 18 as well as the optical scanner system 10 described herein are particularly relevant in that the present invention may be deemed to be an improvement in laser printers. 
     In particular, the present invention comprises a series of scan lenses suitable for use in pre-objective scanning systems where the distance between the scanning deflector and the scan lens is between 40% and 260% of the scan lens focal length. Several embodiments of the current invention are corrected to work in pre-objective scanning optical systems incorporating two deflectors. The aberrations in these is embodiments are corrected over larger pupils than those occupied by the input laser beam to handle the stop-shift effects inherent in the dual deflector scanning systems. These embodiments are also corrected for scan linearity at both deflector positions. The preferred embodiments of this invention are also corrected to minimize line bow over the entire page when the &#34;line&#34; or &#34;fast scan&#34; deflector is a holographic grating and the &#34;slow&#34; or &#34;page&#34; deflector is a galvanometer driven mirror and the line bow for zero page direction deflection is corrected using the method described by B. Narayan in U.S. Pat. No. 4,904,034. That is, the prism is minimizing the line bow when the galvonometer is in its home position (zero page deflector)--i.e. where it is not deflecting at all. The additional correction is performed by a scan lens as deflection is performed in a page deflection. 
     The present invention includes embodiments having two different focal lengths. When used with a pre-objective dual-deflector scanning system disclosed here, these embodiments produce high quality images over standard microform formats. These formats are: 
     
         24X Format: 9.00 mm×11.64 mm; 
    
     
         42X Format: 8.46 mm×6.65 mm; and 
    
     
         48X Format: 7.42 mm×5.82 mm. 
    
     It is desirable to change the image size by replacing one scan lens with another scan lens having a different focal length. Thus, according to a preferred embodiment of the present invention, the locations of the entrance pupils and image plane for the second scan lens remain in the same location as for the first scan lens, despite the change in focal length from one scan lens to another. 
     Thus, the preferred embodiments of the current invention share the same location for scanning deflectors and image plane although they have different focal lengths. This allows easy substitution of scan lenses to change the format over which the image is written. 
     One scan lens is used for both the 42X and the 48X mode. This lens is replaced by a second lens when the scan system is operating at a 24X mode. The focal length of the 42X/48X lens is approximately 27 mm. The focal length of the 24X lens is approximately 54 mm. Multiple embodiments for the scan lenses of both focal lengths are presented here. 
     Reference will now be made to FIG. 1, wherein it will be seen that laser printer compatible optical scanner systems of the present invention comprises: 1) a light source 12, such as a laser or a laser diode 14 for providing a largely collimated light beam 16; 2) a holographic grating scanner H for scanning a surface to be scanned (i.e. a writing surface) in one direction (line direction); 3) a galvo mirror G for scanning this surface in another direction (page direction); and 4) the scan lens or the scanning lens system (or f/θ lens) 18 for focusing the deflected light beam 16 on the aforementioned writing surface WS, such as paper or film. 
     FIGS. 3 and 4 illustrate the back portion of the optical scanner 10, including scan lens 18. These figures show a scan at zero page and zero line direction. All distances d i  are measured in mm and are measured along the chief ray at zero holographic grating and galvo rotation. FIG. 7 shows the same view but at the maximum galvo rotation, zero holographic grating rotation. FIG. 8 shows zero galvo rotation, maximum holographic grating rotation. 
     More specifically (with reference to FIGS. 2-8), according to this embodiment, a gas laser 14 (λ=632.8 μm) provides an essentially collimated beam 16. A laser diode could also be used if appropriate beam-shaping optics is used. Laser beam 16 then passes through an optical train OT, including an acousto-optic modulator (AOM) and a beam-shaping optics and assumes an elliptical cross-section. Specifically, an optical train comprises: i) folding mirrors M1 and M2 for folding the beam in order to produce a compact optical system; ii) a focusing lens L1 for focusing a laser beam 16 at a predetermined location, thereby producing a waste W 1  of predetermined size; iii) a modulator such as an acousto-optic modulator (AOM) for modulating the laser beam 16, another lens L2 having its focus located at the waist location for collimating the beam; and iv) beam expanding optics L3 and L4 for expanding the beam size as needed. The laser beam 16 assumes an elliptical cross-section upon leaving the modulator AOM and has and still has an elliptical cross-section as it leaves the beam expanding optics L3 and L4. The beam 16 then passes through an elliptically-shaped aperture AP (FIGS. 2 and 3) and impinges on a fold mirror M3. The elliptically-shaped aperture&#39;s diameter is 9.56 mm×5.98 mm (line x page). The distance d 1  from the aperture AP to the fold mirror M3 is 143.073 mm. The reflective surface of the fold mirror M3 is inclined at an angle θ=57°. The fold mirror M3 (FIG. 3) folds the beam 16 and directs it at the appropriate angle towards a holographic grating scanner H or hologon H. The distance d 2  between the fold mirror M3 and the holographic grating scanner H is 14.562 mm. 
     The holographic grating scanner H is mounted on a spindle S (FIG. 2) and is spun by it. The spindle is connected to a motor MOT which imparts it with a rotational movement. The rear surface S 2H  of the hologon H contains several facets or gratings HG. As the facet HG swings by, the beam 16 moves in the line direction scanning the writing surface. However, absent corrective optics, the resultant line will not be a straight line, but a curved one-i.e. it will be &#34;bowed&#34; instead. This &#34;bow&#34; is corrected by a prism P located behind the hologon H. 
     The holographic grating scanner H (or the hologon H) comprises a body of optically transparent material having an index of refraction 1.54266 (at λ=632.8 μm). It has a front plano surface S 1H  and a rear surface S 2H . The body of the hologon forms a substrate 6.35 mm thick and it is also inclined an angle θ=57°. As stated above, the rear surface of the hologon, S 2H , has a number holographic gratings HG. The light beam, such as the laser beam 16 impinges on a hologon, refracts through a plano refractive surface S 1H , passes through the body of the hologon and impinges on a rear surface S 2H  which has a holographic grating HG. The directions of the object plane wave and the diffracted order are illustrated in FIG. 5, where θ 1  =θ 2  =33°. In the figure, OPW stands for the object plane wave, RPW stands for the reference wave and DO stands for -1 diffractive order. The construction wavelength is 632.8 μm. 
     The holographic grating HG diffracts and in turn rotates the laser beam by the appropriate amount, eventually providing line scan on the photosensitivity surface such as film, for example. The out coming light beam then passes through the prism P which corrects for the &#34;bow&#34; and which changes the ellipticity of the laser beam cross-section. The distance d 3  between the rear surface S 2H  of the holographic grating scanner and the prism is 19.964 mm. The construction of the prism P is illustrated in FIG. 6. Upon leaving the prism P the light beam 16 is directed towards a galvo mirror G and then impinges on it. At zero galvo mirror G rotation (i.e. at zero galvo position) there is essentially no &#34;bow&#34;. The distance between the prism P and the galvo mirror G is 17.0 mm (measured along the chief ray for no rotation of holographic grating). 
     The galvo mirror G rotates in order to move the beam 16 in an orthogonal direction, thereby providing a scanning function in the page direction. The galvo mirror G is acted upon by a galvanometer which causes the galvo mirror to rotate at the appropriate speed to scan the above mentioned writing surface. The beam 16 reflects from the galvo mirror G towards the lens system 18 which focuses it on the writing surface. The distance between the galvo mirror G and the lens system 18 is 16.870 mm. 
     Thus, according to the present invention, the optical scanner system 10 incorporates two mechanical deflectors. According to this embodiment they are a holographic deflector H and a galvo mirror G. In a laser printing system, the deflector is required to sit in the entrance pupil of the scan lens system for proper operation of the system. The use of two mechanical deflectors imposes special conditions on the location of the entrance pupil for the scan lens 18. Because the optical scanner system uses two optical deflectors, the lens system 18, which is used as a scan lens, is designed to accommodate and to be corrected for two entrance pupil locations--one located at the galvo mirror and another located at the hologon surface S 2H . 
     The optical scanner system 10 illustrated in FIGS. 1-4, 7 and 8 has an F/number (F/#) F/2.82 and the back focal length B.F. of 4.05 mm. The performance parameters and the analysis for the back portion of the optical system (shown in FIGS. 3 and 4) including the scan lens 18 are provided in Table 1. The light beam 16 is a coherent light beam centered around the center wavelength λ=632.8 μm, which corresponds to the HeNe line. 
     
                       TABLE 1______________________________________NOTES:1.  F/# = 2.82    BF = 4.0461    EF = 26.92FORMATS:   48× MODE: 7.758 × 6.244      (HOLOGON × GALVO) (LINE × PAGE)      42× MODE: 8.866 × 7.136      (HOLOGON × GALVO) (LINE × PAGE)2.  CONFIGURATION INFORMATION FOR LENS    BENCH TESTING:DEFLECTION                     BESTMODE         BF      FF        FOCUS  A****Hologon      4.04    -2.83     -.0019 56.662Galvo        4.04    -2.83     -.0019 16.870DEFLECTION   N.P.    N.P.*     X.P.   X.P.*MODE         LOC.    DIAM.     LOC.   DIAM.Hologon      -65.89  9.56      14.69  3.78Galvo        -26.10  6.84**    29.69  6.52**DEFLECTION           LENS      STOP*  REL.*MODE         EF      LENGTH    DIAM.  APER.Hologon      26.92   98.244    9.56   2.82Galvo        26.92   98.244    6.84** 3.93**DEFLECTION   SEMI**   EDGE OFMODE         FIELD    SCANHologon      9.407°                 4.433     (Max. Line Dir.)Galvo        7.571°                 3.563     (Max. Page Dir.)*These quantities are based on the 9.56 and 5.98 mm diametersof the elliptical aperture for the hologon and galvo modedeflection, respectively. NP stands for the entrance pupilwhile XP denotes an exit pupil.**These quantities are adjusted for magnification ofby the prism.***Semi-field angle in scan direction only for 42X mode.Maximum semi-field angle is a compound angle due to bothdeflectors operating simultaneously.****&#34;A&#34; is the distance measured from the front-mostsurface of the filter PL to the entrance pupil location.3.  THIS F-NUMBER IS BASED ON THE FINAL ANGLE    FOR A MARGINAL RAY LIMITED BY THE 9.56    MM DIAMETER OF THE ELLIPTICAL APERTURE.4.  THESE CLEAR APERTURES ARE SUFFICIENT TO    PASS A BUNDLE LIMITED BY THE ELLIPTICAL    APERTURE WHEN THE HOLOGON IS ROTATED BY    8.6296° AND THE GALVO IS ROTATED    BY 3.7857°. THIS CORRESPONDS    TO THE CORNER OF THE    42× FORMAT DEFINED IN NOTE 1.5.  SCAN LINEARITY - HOLOGON SCANNING:HOLOGON ROTATION 1.7259°                    3.4518°                            5.1778°                                  6.9037°DESIRED RAY HT.  0.887   1.773   2.660 3.546ACTUAL RAY HT.   0.884   1.768   2.654 3.542DIFFERENCE       0.003   0.005   0.006 0.005% DIFFERENCE     -0.35   -0.31   -0.24 -0.13HOLOGON ROTATION   7.5511°*                       8.6296°DESIRED RAY HT.    3.879    4.433ACTUAL RAY HT.     3.876    4.433DIFFERENCE         0.003    0.000% DIFFERENCE       -0.08    0.00*Edge of 48× Format.6.  SCAN LINEARITY - GALVO SCANNING:GALVO ROTATION  0.7581°                   1.5162°                           2.2743°                                  3.0324°DESIRED RAY HT. 0.714   1.427   2.141  2.854ACTUAL RAY HT.  0.712   1.425   2.138  2.853DIFFERENCE      0.001   0.002   0.002  0.002% DIFFERENCE    -0.17   -0.15   -0.11  -0.07______________________________________GALVO ROTATION     .3.3167°*                       3.7905°DESIRED RAY HT.    3.122    3.568ACTUAL RAY HT.     3.121    3.568DIFFERENCE         0.001    0.000% DIFFERENCE       -0.04    0.000*Edge of 48× Fomat7.  LINE BOW PERFORMANCE. LINE BOW IS DEFINED    AS THE CHIEF RAY PAGE DIRECTION INTERCEPT    WITH HOLOGON ROTATION MINUS THE CHIEF    RAY PAGE DIRECTION INTERCEPT WITHOUT    HOLOGON ROTATION FOR A FIXED GALVO    ROTATION.         HOLOGON ROTATIONGALVO ROTATION  3.4518°                   6.9037°                           7.5511°                                  8.6296°3.7095°  -0.003  -0.012         -0.0203.3167°                  -0.013*3.0324°  -0.002  -0.010         -0.0161.5162°  -0.001  -0.005         -0.0080.0000°  0.000   0.000          -0.001*Corner of 48× Format.8.  PAGE BOW PERFORMANCE. PAGE BOW IS    DEFINED AS THE CHIEF RAY LINE DIRECTION    INTERCEPT WITH GALVO ROTATION MINUS THE    CHIEF RAY LINE DIRECTION INTERCEPT    WITHOUT GALVO ROTATION FOR A FIXED    HOLOGON ROTATION.GALVO      HOLOGON ROTATIONROTATION   0.0000°              3.4518°                       6.9037°                             7.5511°                                    8.6296°3.7905°      0.000   0.007    0.016        0.0203.3167°                    0.013*3.0324°      0.000   0.005    0.010        0.0131.5162°      0.000   0.001    0.002        0.003*Corner of 48× format.9.  WAVEFRONT PERFORMANCE. SCANNING SYSTEM    RMS OPD COMPUTED FOR A UNIT AMPLITUDE    PLANE WAVE LIMITED BY THE ELLIPTICAL    APERTURE SHOWN IN FIG. 3.         HOLOGON ROTAITONGALVO ROTATION  0.0000°                   1.7259°                           3.4518°                                  5.1778°3.7905°  0.053           0.0523.3167°3.0324°  0.037           0.0412.2743°  0.0231.5162°  0.014           0.0200.7581°  0.0130.0000°  0.014   0.013   0.014  0.022         HOLOGON ROTATAIONGALVO ROTATION  6.9037°                      7.5511°                              8.6296°______________________________________3.7905°  0.038              0.0323.3167°             0.038*3.0324°  0.042      0.0422.2743°1.5162°  0.039      0.0390.7581°0.0000°  0.036      0.036*Corner of 48× format.10.##STR1##W.sub.LINE (in μM)         HOLOGON ROTATIONGALVO ROTATION  0.0000°                   1.7259°                           3.4518°                                  5.1778°3.7905°  1.72            1.693.3167°3.3024°  1.65            1.662.2743°  1.641.5162°  1.63            1.650.7581°  1.640.0000°  1.60    1.66    1.66   1.66         HOLOGON ROTATIONGALVO ROTATION  6.9037°                      7.5511°                              8.6296°3.7905°  1.61               1.673.3167°             1.63*3.3024°  1.64               1.672.2743°1.5162°  1.65               1.700.7581°0.0000°  1.66               1.68W.sub.PAGE (in μM)         HOLOGON ROTATIONGALVO ROTATION  0.0000°                   1.7259°                           3.4518°                                  5.1778°3.7905°  2.29            2.273.3167°3.0324°  2.27            2.262.2743°  2.241.5162°  2.21            2.210.7581°  2.200.0000°  2.34    2.34    2.19   2.21         HOLOGON ROTATIONGALVO ROTATION  6.9037°                      7.5511°                              8.6296°3.7905°  2.24               2.243.3167°             2.24*3.0324°2.2743°1.5162°  2.25               2.280.7581°0.0000°  2.25               2.32______________________________________ 
    
     EMBODIMENTS OF THE SCAN LENS 
     Next, there will be described a modified scan lens (f/θ lens) used in the above-mentioned optical scanner. 
     As stated above, because the optical scanner system uses two optical deflectors, the lens system 18, which is used as a scan lens, is designed to accommodate and to be corrected for two entrance pupil locations--one located at the galvo mirror G and another located at the hologon surface S 2H . The conditions for the lens system 18 (which is also called herein a scan lens or a scan lens system) are: 
     1. The entrance pupil of the scan lens system must be located a great distance in front of the first glass element to allow room for the mechanical deflectors and their associated mechanical features. In the case of the lens system disclosed in Example 1 (Table 2), one of the entrance pupils is located a distance of 2.6 times the focal length in front of the first glass surface. An examination of prior art indicated that there are no designs where the entrance pupil is located at a distance greater than 100% of the focal length. 
     2. The performance of the scan lens must be corrected simultaneously for two different entrance pupil locations corresponding to each mechanical deflector. No designs of this type are known. 
     It should be noted that, although the lens systems described herein are designed specifically for a laser printer system using a holographic deflector and a galvanometer deflector, the two requirements described above are independent of the deflector technology and the lens system such as lens system 18, for example, can be used with any dual deflector pre-objective optical scanner. 
     In addition, the design of a scan lens requires resolution of the following three problems: 
     1. It is important that the linear velocity of the spot across the photosensitive medium such as film remain proportional to the angular velocity of the deflector to achieve uniform power density incident on the film during the scan. 
     2. Holographic grating scanners introduce line bow into the scan line. It is important to keep this line bow minimized to an acceptable level. This problem is more complicated in a scanner with two deflectors because the distortion of the scan lens, which controls the scan linearity described in item 2, causes differing amounts of line bow at each page location. The distortion of the scan lens must be carefully tailored to provide both acceptable scan linearity and acceptable line bow. 
     3. The correction of the point-to-point aberrations must be small enough that the size of the spot produced by the laser does not grow appreciably over the film during scanning. These aberrations are generally measured in OPD (Optical Path Difference) terms for scanning systems. For scanners using two deflectors, it is important that the OPD remains well corrected during deflection of the beam by either scanner. 
     The scan lens 18 of the preferred embodiments comprises three groups(or units), each group being possibly comprised of a plurality of lenses. The three groups are: 
     1. a negative group, comprising one or more lens components. This negative group is located closest to the scanning deflector. 
     2. a weaker positive group, comprising one or more lenses, which is located behind the negative group. 
     3. a stronger positive group, comprising one or more lenses which is located closest to the image plane. 
     It is preferred that the focal lengths of the three groups satisfy the following relationships: ##EQU2## where efl is the focal length of the scan lens, efl 1  is the focal length of the first group, efl 2  is the focal length of the first group, and efl 3  is the focal length of the first group. 
     The scan lens is not symmetrical because the stop position is located at such a great distance from the lens. Consequently, coma can only be corrected by balancing it with spherical aberration. It is preferred that the first negative group in the scan lens introduces this spherical aberration. It is also preferred that coma and astigmatism be introduced by the first negative group in order to achieve correction of scan linearity for the scan lens as a whole. 
     When the first group consists of a single lens element, it is preferred that this lens element meet the following conditions to introduce the correct amount of these aberrations when the entrance pupil is located at distances greater than 150% of focal length of the scan lens: 
     
         0.58≦X≦0.65; 
    
     where X is the bending, given by: 
     
         X=(c.sub.1 +c.sub.2)/(c.sub.1 -c.sub.2); 
    
     where c 1  and c 2  are the curvatures of the first and second surface of the lens element. The term &#34;bending&#34; means changing the shape of the lens element without changing its power. 
     For the case where the first group contains multiple elements, it is preferable that the first lens element of the group meet the following bending conditions: 
     
         0.82≦X≦1.02. 
    
     The second lens group of the preferred embodiment completely corrects the lens for scan linearity. It also reduces the backward curving Petzval introduced by the first group, and partially corrects the astigmatism and spherical. Coma is reduced, but not completely corrected, by this group. In order to balance aberrations, it is preferred that the three elements in the second group meet the following conditions when the entrance pupil is located at distances greater than 150% of the focal length of the scan lens: 
     
         -1.70≦X&#39;.sub.1 ≦-0.94; 
    
     
         -0.46≦X&#39;.sub.2 ≦-0.26; and 
    
     
         -1.98≦X&#39;.sub.3 ≦5.22, 
    
     where X&#39; 1 , X&#39; 2 , and X&#39; 3  represent the bending of the first, second and third element in the second group, respectively. The bending X i  is defined by: 
     
         X&#39;.sub.i =(c.sub.1 +c.sub.2)/(c.sub.1 -c.sub.2); 
    
     where c 1  and c 2  are the curvatures of the first and second surface of a lens element of the second lens groups. 
     It is preferred that the third lens group corrects the remaining coma. This group slightly reduces Petzval, astigmatism, and spherical as well, out most of this correction is done by the second group. The third group is also used to correct the line bow when a holographic grating is used to control the fast scan direction. This group is comprised of a plurality of elements. When two elements are used, good correction can be achieved under the following bending conditions: 
     
         -3.11≦X&#34;.sub.1 ≦2.56; and 
    
     
         2.05≦X&#34;.sub.2 ≦2.21, 
    
     where X&#34; 1  is the bending of the first lens component of the third lens group and X&#34; 2  is the bending of the second lens component of the second group. 
     These scan lens aberrations are well corrected for any combination of rotations by both deflectors. This required that the performance be corrected when the stop is shifted between the locations of the two deflectors. Since the chief ray moves transversely as the stop is shifted longitudinally, the aberrations of the scan lens are corrected over a larger pupil diameter than the actual diameter of the laser beam entering the scan lens. This is shown in FIGS. 20 and 21. More specifically: 
     FIG. 20A shows the transverse aberration over the portion of the pupil used by the holographic grating deflector at an image height of 3.57 mm. Pupil is taken at the position of the holographic grating. The scan lens is described in Example 1; 
     FIG. 20B shows the transverse aberration over the portion of the pupil used by the galvo deflector at an image height of 3.57 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20C shows the transverse aberration over the portion of the pupil used by the holographic grating deflector at an image height of 2.85 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20D shows the transverse aberration over the portion of the pupil used by the galvo deflector at an image height of 2.85 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20E shows the transverse aberration over the portion of the pupil used by the holographic grating deflector at an image height of 1.43 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20F shows the transverse aberration over the portion of the pupil used by the galvo deflector at an image height of 1.43 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20G shows the transverse aberration over the portion of the pupil used by the holographic grating deflector at an image height of 0 mm. Pupil is taken at the position of the holographic grating; 
     FIG. 20H shows the transverse aberration over the portion of the pupil used by the galvo deflector at an image height of 0 mm. Pupil is taken at the position of the holographic grating; and 
     FIG. 21 illustrates stop shift effects due to the use of two deflectors for the scan lens described in Example 1. 
     Correcting for this larger pupil size requires more elements in the second group. Note that embodiment eleven, which uses two elements in the second groups, does not correct for this condition. 
     The present invention allows scanning deflectors in scanning systems to be located at a greater distance from the scan lens than prior art. In particular, the scanning deflectors may be located at a distance of 260% of the scan lens focal length. 
     The present invention allows two scanning deflectors to be used in pre-objective scanning systems, where one deflector provides the &#34;line&#34; or &#34;fast-scan&#34; scanning and the other deflector provides the &#34;page&#34; or &#34;slow-scan&#34; scanning. The aberrations of the lens system of the present invention are corrected to provide high quality images and scan linearity over the entire image. 
     The present invention allows the use of a holographic grating for the line direction scanning deflector and a galvonometer driven mirror for the page direction scanning deflector in a dual-deflector pre-objective scanning system. Furthermore, the line bow produced by the holographic grating is corrected over the entire image provided the line bow at zero page direction deflection has been corrected by a prism as described by B. Narayan. It is preferred that the scan lens have three lens elements in the rear group to correct the point-to-point aberrations, scan linearity, and line bow. These three lens elements must meet the following bending conditions: 
     
         -1.90≦X&#34;.sub.1 ≦-1.80; 
    
     
         1.55≦X&#34;.sub.2 ≦1.65; and 
    
     
         5.30≦X&#34;.sub.3 ≦5.55. 
    
     The present invention includes lenses of different focal lengths having shared scanning deflector positions and image plane positions to allow easy substitution of scan lenses in a scanning system to alter the image size produced by the scanner. 
     More specifically, the above-mentioned f/θ lenses or scan lenses comprise, in order from an object side: a) a first group, comprising a negative lens component C1&#39; with a concave surface S1 towards the object side. This lens element C1&#39; may be in a form of a biconcave lens component or lens element or a meniscus lens component lens element. It may also be a plano/concave component; b) a second group including at least two positive lens components C2&#39;, C3&#39;, the lens component nearest to the object side being a first positive lens component or a lens element having a convex surface oriented to the image side, this first positive lens component may be in a form of a meniscus positive lens element, the other lens component being a second positive lens component C3&#39; having a convex surface oriented towards the object side. The second positive lens component C3&#39; may be a biconvex lens component or a plano-convex lens component or even a meniscus lens component; and c) a third group including a thick meniscus lens component C4&#39; having its convex surface oriented towards the object side and its concave surface oriented towards the image side. This third group may also include a small lens component C5&#39; located between said thick meniscus lens component and an image surface. The small lens component has a convex surface facing said thick lens component and may have meniscus, biconvex or convex/plano shape. 
     The above described lens system has a minimum required number of lens components. Many of the embodiments described below will have one or more additional lens components. 
     To summarize, this lens system of the preferred embodiment has two entrance pupil positions. The entrance pupils are located in front of the front-most lens component C1&#39;. Lens component C1&#39; has negative optical power and is used to introduce spherical aberrations into the lens system in order to balance coma. The second group includes two to four lens elements, having a large radius of curvature on average. It is used to correct for scan linearity and to partially correct spherical aberration and coma. The function of the third group is to correct the remaining coma and to reduce other residual aberrations. 
     The scan lens (or the lens system) 18 of the first preferred embodiment is shown in FIG. 9. The lens system 18 includes a plano-parallel plate PL with no optical power. It has a front most surface S1 and a rear surface S2. The Plate PL serves as a filter and reduces the power of the laser beam 11. It is made from an ordinary crown filter glass. The space A between the entrance pupil position (or the aperture stop AS) and the filter PL has two values corresponding to each of the two deflector positions. The lens system 18 includes seven lens components C1-C7. 
     The first lens component C1 is a cemented doublet. This cemented doublet comprises a front (i.e. object side) lens element E1 of negative optical power K1, and a second lens element E2. Although the optical power K2 of the lens element E2 also is negative, in this preferred embodiment it is significantly smaller than K1. More specifically, K2/K1≈0.1. The front surface S3 of the lens component C1 is concave and faces the object side. The rear surface S5 of the lens component C1 is slightly concave. Its (absolute) radius of curvature is larger than that of the surface S3. The surface denoted as S4 is an internal interface surface where the elements E1 and E2 are cemented. 
     The second optical component C2 is a positive power lens element E3. The lens element E3 is a meniscus lens element. It has a front concave surface S6 and a rear (or image side) convex surface S7. 
     The third optical component C3 is a positive power lens element E4. The lens element E4 is biconvex. It has a front convex surface S8 and a rear convex surface S9. 
     The fourth optical component C4 is a positive power lens element E5. The lens element E5 is a meniscus lens element. It has a front convex surface S10 and a rear (or image side) concave surface S11. 
     The fifth optical component C5 is a positive power lens element E6. The lens element E6 is a meniscus lens element. It has a front convex surface S12 and a rear (or image side) concave surface S13. 
     The sixth optical component C6 is a negative power lens element E7. The lens element E7 is a meniscus lens element. It has a front convex surface S14 and a rear (or image side) concave surface S15. 
     The seventh optical component C7 is a positive power lens element E8. The lens element E8 is a meniscus lens element. It has a front convex surface S16 and a rear (or image side) concave surface S17. 
     The specific parameters for the scan lens 18 are provided in Table 2. All dimensions are in millimeters. 
     The first preferred embodiment of the scan lens 18 provided for use with an optical scanner 10 is illustrated in FIG. 9. In the drawing, the surfaces S are numbered by sub scripts from front (or object side) of the lens system 18 to the rear, or the image side of the lens system 18. In the table (Table 2), the thickness of the lens elements T and the spacings between elements, including the variable space A, are also located from front to rear. In the tables, spacings and thicknesses are listed in the same line as the surface preceding the thickness or the spacing. All indices N correspond to wavelength λ=587.6 μm. V d  is the abbe number of the lens elements, which according to a standard definition is: ##EQU3## 
     EXAMPLE 1 
     
                                           TABLE 2__________________________________________________________________________    CLEAR AXIAL        THICK-                       INDEX                            V-SURF.    APER. (5)     BEAM RADIUS  NESS N.sub.d                            NUMBER                                  GLASS__________________________________________________________________________9.56 9.56 DIAPHRAGM                  A1   28.80 9.56 PLANO   2.000                       1.517                            64.2  BK-7 (Filter)2   29.29 9.56 PLANO   7.2293   30.07 9.56 -24.5755                  2.810                       1.501                            56.4  K-104   36.02 9.99 1212.26 6.334                       1.847                            23.8  SFL-575   39.94 10.66          372.272 7.2226   47.26 12.21          -205.807                  13.500                       1.847                            23.8  SFL-577   53.40 14.13          -54.4437                  1.0008   58.41 14.21          255.486 14.321                       1.847                            23.8  SFL-579   59.72 14.23          -96.7395                  1.00010  56.43 14.02          55.2834 13.792                       1.847                            23.8  SFL-5711  50.07 11.55          86.0143 1.00012  45.97 11.27          34.7582 9.740                       1.847                            23.8  SFL-5713  40.10 8.70 50.4295 3.00014  36.92 7.65 50.7879 15.000                       1.847                            23.8  SFL-5715  20.27 3.74 15.0430 5.75716  17.99 2.22 17.8527 3.768                       1.847                            23.8  SFL-5717  16.55 1.46 76.2142__________________________________________________________________________ NOTES: 1. Entrance pupil locations are provided in Table 1. ##STR2## where EP1 is the airequivalent distance to a holographic deflector and EP.sub.2 is the airequivalent distance to a galvo deflector. 
    
     As stated above, the design of a scan lens requires solving three problems: 
     1. It is important that the linear velocity of the spot across the photosensitive medium such as film remain proportional to the angular velocity of the deflector to achieve uniform power density incident on the film during the scan. The scan linearity performance of the scan lens 18 of the first embodiment is shown in the plots of FIG. 22 for scanning by both the holographic grating and the galvo mirror. The vertical axis is the departure from linearity in mm, while the horizontal axis measures degrees of rotation. 
     2. Holographic grating scanners introduce line bow into the scan line. It is important to keep this line bow minimized to an acceptable level. This problem is more complicated in a scanner with two deflectors because the distortion of the scan lens, which controls the scan linearity described in item 2, causes differing amounts of line bow at each page location. The distortion of the scan lens must be carefully tailored to provide both acceptable scan linearity and acceptable line bow. Line bow characteristics for the scan lens 18 of the first preferred embodiment are shown in FIG. 23. 
     3. The correction of the point-to-point aberrations must be small enough that the size of the spot produced by the laser does not grow appreciably over the film during scanning. These aberrations are generally measured in OPD (Optical Path Difference) terms for scanning systems. For scanners using two deflectors, it is important that the OPD remains well corrected during deflection of the beam by either scanner. FIGS. 24 and 25 show the OPD correction as a function of holographic grating rotation and galvo mirror rotation for the scan lens 18 of the first preferred embodiment. Specifically, FIG. 24 shows OPD for zero galvo mirror rotation while FIG. 25 shows OPD for zero holographic grating rotation. 
     Finally, FIG. 26 shows the optical performance of the optical system in the comer of the largest format. FIG. 26 is a wavefront contour map for a galvo rotation of 7.55°, holographic grating rotation of 3.32° and X image=3.11 mm, Y image=3.88 mm. This is the maximum field coverage of the scan lens 18. As we can see from the plot, peak-to-valley (P-V) OPD is 0.2023 waves, which corresponds to the RMS (root mean square) OPD of 0.03836 waves. 
     Although the above analysis was performed for the optical scan system incorporating the lens system (18) of the first embodiment, the analysis results are also representative of what is possible to achieve with the other similar scan lenses. 
     The second preferred embodiment of the scan lens is a lens system 18a. It is illustrated in FIG. 10. It&#39;s parameters are provided in Table 3. 
     This lens system has a focal length of 27 mm, is capable of working in 42X as well as in 48X mode and has F-numbers F/2.96-F/3.66. 
     The lens system 18a includes 6 lens components C1a-C6a. 
     The first lens component C1a is a negative power lens component. It corresponds to a biconcave lens element E1a. The front surface S1 of the lens component C1a is concave and faces the object side. The rear surface S2a of the lens component C1a is also concave. 
     The second optical component C2a is a positive power lens element E2a. The lens element E2a is a meniscus lens element. It has a front concave surface S3a and a rear (or image side) convex surface S4a. 
     The third optical component C3a is a positive power lens element E3a. The lens element E3a is biconvex. It has a front convex surface S5a and a rear convex surface S6a. 
     The fourth optical component C4a is a positive power lens element E4a. The lens element E4a is a meniscus lens element. It has a front convex surface S7a and a rear (or image side) concave surface S8a. 
     The fifth optical component C5a is a positive power lens element E5a. The lens element E5a is a meniscus lens element. It has a front convex surface S9a and a rear (or image side) concave surface S10a. 
     The sixth optical component C6a is a positive power lens element E6a. The lens element E6a is a meniscus lens element. It has a front convex surface S11a and a rear (or image side) concave surface S12a. 
     EXAMPLE 2 
     
                                           TABLE 3__________________________________________________________________________    CLEAR    AXIAL        THICK-    V-    SPECIALSURF.    APER.    BEAM RADIUS  NESS INDEX                           NUMBER                                 NOTES__________________________________________________________________________    9.14 9.14 DIAPHRAGM                 A1   29.14    9.14 -29.7505                 10.231                      1.517                           64.2  BK-72   38.31    10.26         111.735 9.2973   47.76    12.17         -3043.89                 8.200                      1.805                           25.4  SF-64   50.44    13.10         -81.1064                 0.1505   53.86    13.15         242.253 9.000                      1.805                           25.4  SF-66   54.58    13.33         -90.6475                 0.2007   53.33    13.26         51.9944 8.500                      1.805                           25.4  SF-68   50.66    11.95         92.1109 0.1509   46.91    11.86         32.3631 24.858                      1.805                           25.4  SF-610  23.53    5.33 15.3355 6.54311  21.55    4.07 17.5232 9.000                      1.805                           25.4  SF-612  16.17    2.17 40.7438__________________________________________________________________________TWO ENTRANCE PUPILS ##STR3##NOTES:  F/#= 2.96-3.66  EF = 27.00FORMATS: 48× MODE: 7.874 × 6.187 (HOE × GALVO)    42× MODE: 8.738 × 6.865 (HOE × GALVO)  CONFIGURATION INFORMATIONEF         BE  FF         BEST FOCUS                             A27.00      6.34          3.47       -.0015  70.00027.00      6.34          3.47       -.0015  70.00027.00      6.34          3.47       -.0015  24.00027.00      6.34          3.47       -.0015  24.000      N.P.          N.P.       X.P.    X.P.EF         LOC.          DIAM.      LOC.    DIAM.27.00      -70.00          9.14       17.30   3.7127.00      -70.00          7.37       17.30   2.9927.00      -24.00          9.14       41.86   12.0227.00      -24.00          7.37       41.86   9.69LENS    STOP REL.  SEMI  SEMIEE   LENGTH  DIAM.             APER. FIELD DIAG.                              DESCRIPTION27.0086.129  9.14 2.96  8.41 DEGHOE @                         3.93 48×                              EN PUPIL27.0086.129  7.37 3.66  9.34 DEGHOE @                         4.36 42×                              EN PUPIL27.0086.129  9.14 2.96  6.62 DEGGALVO                         3.10 48×                              @ EN PUPIL27.0086.129  7.37 3.66  7.34 DEG                         3.44 42× GALVO                              EN PUPIL  PERFORMANCE48×- HOE @ EN PUPILANGLE         1.6340             3.2681                   4.9027                       6.5379                             8.1741                                 8.4079DESIRED RAY HT.         .7656             1.5311                   2.2966                       3.0621                             3.8277                                 3.9370ACTUAL RAY HT.         .7698             1.5380                   2.3032                       3.0642                             3.8205                                 3.9281DIFFERENCE    -.0042             -.0069                   -.0066                       -.0021                             +.0072                                 +.0089RMS OPD       .0073             .0044 .0009                       .0033 .0038                                 .0040HOE @ EN PUPILANGLE         1.6340             3.2681                   4.9027                       6.5379                             8.1741                                 9.3401DESIRED RAY HT.         .7648             1.5296                   2.2944                       3.0592                             3.8241                                 4.3688ACTUAL RAY HT.         .7698             1.5380                   2.3032                       3.0642                             3.8205                                 4.3561DIFFERENCE    -.0050             -.0084                   -.0088                       -.0050                             +.0036                                 +.0127RMS OPD       .0050             .0031 .0005                       .0026 .0036                                 .0069GALVO EN PUPIL (EQUIV. FOCAL LENGTH = 26.895)ANGLE         1.1010             2.2021                   3.3031                       4.4041                             5.5052                                 6.6062F-TH          -.0021             -.0035                   -.0038                       -.0028                             +.0001                                 +.0052COMPLIANCERMS OPD       .0074             .0050 .0034                       .0051 .0063                                 .0048GALVO @ EN PUPIL (EQUIV. FOCAL LENGTH = 26.873)ANGLE         1.2231             2.4462                   3.6693                       4.8924                             6.1155                                 7.3387F-TH          -.0027             -.0047                   -.0052                       -.0038                             +.0002                                 +.0070COMPLIANCERMS OPD       .0049             .0030 .0023                       .0036 .0036                                 .0047__________________________________________________________________________ 
    
     The third preferred embodiment of the scan lens is a lens system 18b. It is illustrated in FIG. 11. It&#39;s parameters are provided in Table 4. 
     This lens system has a focal length of 53.59 mm, has a semifield angle 8.46-6.61 degrees and is designed for 24X magnification. It has an F-numbers F/5.87. 
     The lens system 18b includes 5 lens components C1b-C5b. 
     The first lens component C1b is a negative power lens component. It corresponds to a biconcave lens element E1b. The front surface S1b of the lens component C1b is concave and faces the object side. The rear surface S2b of the lens component C1b is also concave. 
     The second optical component C2b is a positive power lens element E2b. The lens element E2b is a meniscus lens element. It has a front concave surface S3b and a rear (or image side) convex surface S4b. 
     The third optical component C3b is a positive power lens element E3b. The lens element E3b is biconvex. It has a front convex surface S5b and a rear convex surface S6b. 
     The fourth optical component C4b is a positive power lens element E4b. The lens element E4b is a meniscus lens element. It has a front convex surface S7b and a rear (or image side) concave surface S8b. 
     The fifth optical component C5b is a positive power lens element E5b. The lens element E5b is a meniscus lens element. It has a front convex surface S9b and a rear (or image side) concave surface S10b. 
     EXAMPLE 3 
     
                                           TABLE 4__________________________________________________________________________    CLEAR    AXIAL        THICK-    V-    SPECIALSURF.    APER.    BEAM RADIUS  NESS INDEX                           NUMBER                                 NOTES__________________________________________________________________________9.14    9.14 DIAPHRAGM                 A1   28.83    9.14 -31.9220                 9.282                      1.517                           64.2  BK-72   36.26    10.09         124.409 5.1303   40.34    11.05         PLANO   10.025                      1.785                           26.1  SF-564   43.68    12.09         -61.8929                 0.2565   46.66    12.12         86.1752 10.969                      1.785                           26.1  SF-566   46.47    11.69         -164.430                 0.1607   44.39    11.61         47.4251 24.959                      1.785                           26.1  SF-568   29.74    7.15 26.1336 7.1889   29.44    6.41 50.1784 6.125                      1.517                           64.2  BK-710  28.46    5.73 PLANO__________________________________________________________________________TWO ENTRANCE PUPILS ##STR4##NOTES:  F/# = 5.87  EF = 53.59FORMAT IS 12.358 × 15.750 (GALVO × HOE)  CONFIGURATION INFORMATIONEF         BF  FF         BEST FOCUS                             A53.59      33.52          32.39      -.007   70.00053.59      33.52          32.39      -.007   24.000      N.P.          N.P.       X.P.    X.P.EF         LOC.          DIAM.      LOC.    DIAM.53.59      -70.00          9.14       109.88  13.0253.59      -24.00          9.14       -308.93 53.38LENS    STOP REL.  SEMI  SEMIEF   LENGTH  DIAM.             APER. FIELD DIAG.                              DESCRIPTION53.5974.094  9.14 5.87  8.42 DEG                         7.875                              HOE &amp;                              ENTRANCE                              PUPIL53.5974.094  9.14 5.87  6.61 DEG                         6.179                              GALVO &amp;                              ENTRANCE                              PUPIL  PERFORMANCEHOE @ ENTRANCE PUPILANGLE (DEG.)  .5446             2.1786                   3.8129                       5.4477                             7.0832                                 8.4169DESIRED RAY HT.         .5105             2.0396                   3.5687                       5.0978                             6.6269                                 7.8740ACTUAL RAY HT.         .5094             2.0378                   3.5662                       5.0950                             6.6254                                 7.8754DIFFERENCE    +.0011             +.0018                   +.0025                       +.0028                             +.0015                                 -.0014RMS OPD       .0079             .0048 .0017                       .0039 .0060                                 .0072GALVO @ ENTRANCE PUPIL (EQUIV. FOCAL LENGTH = 53.588)ANGLE         1.1010             2.2021                   3.3031                       4.4041                             5.5052                                 6.6062F-TH          -.0001             -.0002                   -.0001                       +.0001                             +.0002                                 -.0001COMPLIANCERMS OPD       .0072             .0048 .0021                       .0025 .0040                                 .0053__________________________________________________________________________ 
    
     The fourth preferred embodiment of the scan lens is a lens system 18c. It is illustrated in FIG. 12. It&#39;s parameters are provided in Table 5. 
     This lens system has a focal length of 53.79 mm, is designed to provide 24X magnification and has F-number F/5.87. 
     The lens system 18c comprises only four lens components C1c-C4c. 
     The first lens component C1c is a negative power lens component. It corresponds to a biconcave lens element E1c. The front surface S1c of the lens component C1c is concave and faces the object side. The rear surface S2c of the lens component C1c is also concave. 
     The second optical component C2c is a positive power lens element E2c. The lens element E2c is a meniscus lens element. It has a front concave surface S3c and a rear (or image side) convex surface S4c. 
     The third optical component C3c is a positive power lens element E3c. The lens element E3c is biconvex. It has a front convex surface S5c and a rear convex surface S6c. 
     The fourth optical component C4c is a positive power lens element E4c. The lens element E4a is a meniscus lens element. It has a front convex surface S7c and a rear (or image side) concave surface S8c. 
     EXAMPLE 4 
     
                                           TABLE 5__________________________________________________________________________    CLEAR    AXIAL        THICK-    V-    SPECIALSURF.    APER.    BEAM RADIUS  NESS INDEX                           NUMBER                                 NOTES__________________________________________________________________________9.17    9.17 DIAPHRAGM                 A1   28.65    9.17 -26.7829                 9.134                      1.501                           56.4  K-102   36.75    10.27         698.300 5.0343   38.96    11.14         -75.4793                 10.140                      1.805                           25.4  SF-64   44.54    12.79         -47.6110                 0.1855   48.39    12.85         282.120 11.083                      1.805                           25.4  SF-66   49.71    13.12         -74.9060                 0.1757   48.40    13.05         70.9840 25.042                      1.805                           25.4  SF-68   39.37    9.71 109.834__________________________________________________________________________TWO ENTRANCE PUPILS ##STR5##NOTES:  F/#= 5.87  EF = 53.79FORMATS 12.358 × 15.750 (GALVO × HOE)  CONFIGURATION INFORMATIONEF         BF  FF         BEST FOCUS                             A53.79      56.90          25.79      -.0055  70.00053.79      56.90          25.79      -.0055  24.000      N.P.          N.P.       X.P.    X.P.EF         LOC.          DIAM.      LOC.    DIAM.53.79      -70.00          9.17       122.34  11.1653.79      -24.00          9.17       1561.62 275.89__________________________________________________________________________LENS    STOP REL.  SEMI  SEMIEF   LENGTH  DIAM.             APER. FIELD DIAG.                              DESCRIPTION53.5960.793  9.17 5.87  8.42 DEG                         7.875                              HOE @                              ENTRANCE                              PUPIL53.7960.793  9.17 5.87  6.61 DEG                         6.179                              GALVO @                              ENTRANCE                              PUPIL  PERFORMANCEHOE @ ENTRANCE PUPILANGLE (DEG.)  .5446             2.1786                   3.8129                       5.4477                             7.0832                                 8.4169DESIRED RAY HT.         .5105             2.0396                   3.5687                       5.0978                             6.6269                                 7.8740ACTUAL RAY HT.         .5113             2.0448                   3.5765                       5.1048                             6.6277                                 7.8630DIFFERENCE    -.0008             -.0052                   -.0078                       -.0070                             -.0008                                 +.0110RMS OPD       .0070             .0074 .0073                       .0011 .0141                                 .0149GALVO @ ENTRANCE PUPIL (EQUIV. FOCAL LENGTH = 53.686)ANGLE (DEG.)  1.1010             2.2021                   3.3031                       4.4041                             5.5052                                 6.6062F-TH          -.0020             -.0035                   -.0041                       -.0031                             -.0001                                 +.0057COMPLIANCERMS OPD       .0071             .0074 .0072                       .0079 .0111                                 .0143__________________________________________________________________________ 
    
     The fifth preferred embodiment of the scan lens is a lens system 18d. It is illustrated in FIG. 13. Its parameters are provided in Table 6. 
     This lens system has a focal length of 53.55 mm, is designed to provide 24X magnification and has an F-number F/5.86. 
     The lens system 18d includes 5 lens components C1d-C5d. 
     The first lens component C1d is a negative power lens component It corresponds to a biconcave lens element E1d. The front surface S1d of the lens component C1d is concave and faces the object side. The rear surface S2d of the lens component C1d is also concave. 
     The second optical component C2a is a positive power lens element E2d. The lens element E2d is a meniscus lens element. It has a front concave surface S3d and a rear (or image side) convex surface S4d. 
     The third optical component C3d is a positive power lens element E3a. The lens element E3d is a meniscus lens element. It has a front convex surface S5d and a rear slightly convex surface S6d. 
     The fourth optical component C4d is a positive power lens element E4d. The lens element E4d is a meniscus lens element. It has a front convex surface S7d and a rear (or image side) concave surface S8d. 
     The fifth optical component C5a is a positive power lens element E5a. The lens element E5a is a biconvex lens element. It has a front convex surface S9a and a rear (or image side) convex surface S10a. 
     EXAMPLE 5 
     
                                           TABLE 6__________________________________________________________________________    CLEAR    AXIAL        THICK-    V-    SPECIALSURF.    APER.    BEAM RADIUS  NESS INDEX                           NUMBER                                 NOTES__________________________________________________________________________9.14    9.14 DIAPHRAGM                 A1   28.60    9.14 -26.4006                 4.000                      1.517                           64.2  BK-72   33.96    9.66 258.050 5.0193   37.88    10.65         -204.615                 9.000                      1.805                           25.4  SFL-64   40.86    11.81         -41.9665                 0.2305   44.09    11.82         53.7493 9.000                      1.805                           25.4  SFL-66   43.07    11.04         1117.65 0.2087   40.62    10.95         35.5605 12.000                      1.847                           23.8  SFL-578   31.20    8.25 23.3570 7.2399   30.87    7.46 72.3748 6.126                      1.517                           64.2  BK-710  29.89    6.79 -1117.65__________________________________________________________________________NOTES:  F/# = 5.86  EF = 53.55FORMAT IS 12.358 × 15.750 (GALVO × HOE) ##STR6##WHERE A.sub.1 IS THE DISTANCE TO THE HOLOGRAPHIC DEFLECTORAND A.sub.2 IS THE DISTANCE TO A GALVO DEFLECTOR.  CONFIGURATION INFORMATIONEF         BF  FF         BEST FOCUS                             A53.55      39.66          36.32      -.011   70.00053.55      39.66          36.32      -.011   24.000      N.P.          N.P.       X.P.    X.P.EF         LOC.          DIAM.      LOC.    DIAM.53.55      -70.00          9.14       124.80  14.5253.55      -24.00          9.14       193.12  39.71LENS    STOP REL.  SEMI  SEMIEF   LENGTH  DIAM.             APER. FIELD DIAG.                              DESCRIPTION53.5552.822  9.14 5.86  8.42 DEG                         7.86 HOE @                              ENTRANCE                              PUPIL53.5552.822  9.14 5.86  6.61 DEG                         6.18 GALVO @                              ENTRANCE                              PUPIL  PERFORMANCEHOE @ ENTRANCE PUPILANGLE (DEG.)  0.5446             2.1786                   3.8129                       5.4477                             7.0832                                 8.4169DESIRED RAY HT.         0.5105             2.0396                   3.5687                       5.0978                             6.6269                                 7.8740ACTUAL RAY HT.         0.5091             2.0363                   3.5635                       5.0914                             6.6220                                 7.87??DIFFERENCE    0.0015             0.0033                   0.0052                       0.0064                             0.0048                                 -0.0002RMS OPD       0.0098             0.0067                   0.0151                       0.0178                             0.0096                                 0.0173GALVO @ ENTRANCE PUPIL (EQUIV. FOCAL LENGTH = 53.557)ANGLE         1.1010             2.2021                   3.3031                       4.4041                             5.5052                                 6.6062DESIRED RAY HT.         1.0292             2.0584                   3.0876                       4.1167                             5.1460                                 6.1751ACTUAL RAY HT.         1.0290             2.0581                   3.0872                       4.1164                             5.1459                                 6.1757DIFFERENCE    0.0002             0.0003                   0.0004                       0.0004                             0.0001                                 -0.0006RMS OPD       0.0092             0.0067                   0.0049                       0.0062                             0.0067                                 0.0031  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 2 IN Table 3.__________________________________________________________________________ 
    
     The sixth preferred embodiment of the scan lens is a lens system 18e. It is illustrated in FIG. 14. It&#39;s parameters are provided in Table 7. 
     This lens system has a focal length of 27.17 mm, is capable of working in 42X as well as in 48X mode and has an F-number F/2.84. 
     The lens system 18e includes 6 lens components C1e-C6e. 
     The first lens component C1e is a negative power lens component. It corresponds to a biconcave lens element E1e. The front surface S1e of the lens component C1e is concave and faces the object side. The rear surface S2e of the lens component C1e is also concave. 
     The second optical component C2e is a positive power lens element E2e. The lens element E2e is a meniscus lens element. It has a front concave surface S3e and a rear (or image side) convex surface S4e. 
     The third optical component C3e is a positive power lens element E3e. The lens element E3e is biconvex. It has a front convex surface S5e and a rear convex surface S6e. 
     The fourth optical component C4e is a positive power lens element E4e. The lens element E4e is a meniscus lens element. It has a front convex surface S7e and a rear (or image side) concave surface S8e. 
     The fifth optical component C5e is a positive power lens element E5e. The lens element E5e is a meniscus lens element. It has a front convex surface S9e and a rear (or image side) concave surface S10e. 
     The sixth optical component C6e is a positive power lens element E6e. The lens element E6e is a meniscus lens element. It has a front convex surface S11e and a rear (or image side) concave surface S12e. 
     EXAMPLE 6 
     
                                           TABLE 7__________________________________________________________________________    CLEAR AXIAL         THICK-       V-SURF.    APER. (3)     BEAM  RADIUS  THICKNESS                           INDEX                                NUMBER__________________________________________________________________________    9.57  9.57  DIAPHRAGM                   A1   31.90 9.57  -29.0230                   15.000  1.517                                64.22   47.16 11.33 135.811 8.2563   56.47 13.08 -1912.42                   11.500  1.834                                37.24   60.37 14.43 -74.7421                   0.1505   65.87 14.47 216.850 12.518  1.834                                37.26   66.80 14.50 -122.465                   0.2007   64.41 14.41 53.0957 9.500   1.834                                37.28   60.94 12.79 78.6332 0.1509   55.71 12.70 34.4449 24.771  1.834                                37.210  29.58 6.08  17.6500 4.69811  28.58 5.13  21.8514 8.300   1.834                                37.212  24.32 3.33  58.2268__________________________________________________________________________NOTES:  F/# = 2.84  EF = 27.17FORMATS: 1ST FORMAT OF 48X MODE: 7.756 × 6.244 (HOE × GALVO)    2ND FORMAT OF 48X MODE: 6.244 × 7.756 (HOE × GALVO)    1ST FORMAT OF 42X MODE: 8.866 × 7.136 (HOE × GALVO)    2ND FORMAT OF 42X MODE: 7.136 × 8.866 (HOE × GALVO)  CONFIGURATION INFORMATION        BESTCFG  BF  FF  FOCUS             A__________________________________________________________________________1    9.3475    1.76        -.0026             70.0002    9.3475    1.76        -.0026             70.0003    9.3475    1.76        -.0026             24.0004    9.3475    1.76        -.0026             24.000__________________________________________________________________________N.P.    N.P. X.P.             X.P.CFG  LOC.    DIAM.         LOC.             DIAM.__________________________________________________________________________1    -70.00    9.57 20.17              3.812    -70.00    9.57 20.17              3.813    -24.00    9.57 42.55             11.694    -24.00    9.57 42.55             11.69__________________________________________________________________________LENS  STOP REL.               SEMICFG  LENGTH      DIAM.           APER.               FIELD*__________________________________________________________________________1    95.043      9.57 2.84               8.231°2    95.043      9.57 2.84               9.407°3    95.043      9.57 2.84               8.231°4    95.043      9.57 2.84               9.407°__________________________________________________________________________EDGE OF          DEFLECTOR ATCFG  SCAN  MODE FORMAT                 ENTRANCE PUPIL__________________________________________________________________________1    3.887 48X  1ST   HOLOGON2    4.452 42X  1ST   HOLOGoN3    3.870 48X  2ND   GALVO4    4.412 42X  2ND   GALVO__________________________________________________________________________ *Semi-field angle in scan direction only; maximum semifield angle is a compound angle due to both deflectors operating simultaneously. 
    
     
         3.  CLEAR APERTURES ARE SUFFICIENT TO PASS BUNDLES WITH THE  DIAMETER OF THE ENTRANCE PUPIL CENTERED AROUND SKEW CHIEF  RAYS TERMINATING AT THE CORNERS OF THE 42X MODE 1ST AND 2ND  FORMATS.ENTRANCE PUPIL LOCATION = -70.0; GALVO LOCATION = -24.0             GALVO ROT. INCHIEF RAY    RAY ANGLE @             ORTHOGONAL                       IMAGE PLANE                                 DIAGRAMDESCRIPTION    ENTR. PUPIL             DIRECTION RAY INTERCEPT                                 LOCATION__________________________________________________________________________CORNER 42X    9.4069   3.7857    (4.396, 3.496)                                 151ST FMT.CORNER 42X    7.7571   4.7035    (3.629, 4.355)                                 162ND FMT.__________________________________________________________________________  PERFORMANCECONFIGURATION 1 - 48X MODE DEFLECTION BY HOLOGONDIAGRAMLOCATION   2    3    4    5    6    7__________________________________________________________________________ANGLE (DEG.)      1.0893           2.7234                4.3578                     5.9928                          7.6286                               8.2306DESIRED RAY HT.      0.5136           1.2840                2.0544                     2.8245                          3.5941                               3.8786ACTUAL RAY HT.      0.5167           1.2907                2.0620                     2.8294                          3.5915                               3.8703DIFFERENCE -0.0031           -0.0067                -0.0076                     -0.0049                          0.0026                               0.0083RMS OPD    0.0098           0.0061                0.0068                     0.0134                          0.0174                               0.0183__________________________________________________________________________CONFIGURATION 2 - 42X MODE DEFLECTION BY HOLOGONDIAGRAMLOCATION   2    3    4    5    6    7__________________________________________________________________________ANGLE (DEG.)      1.6340           3.2681                4.9027                     6.5379                          8.1741                               9.4069DESIRED RAY HT.      0.7705           1.5411                2.3116                     3.0810                          3.8532                               4.4323ACTUAL RAY HT.      0.7749           1.5481                2.3183                     3.0840                          3.8442                               4.4124DIFFERENCE -0.0044           -0.0070                -0.0067                     -0.0030                          0.0090                               0.0199RMS OPD    0.0088           0.0052                0.0090                     0.0152                          0.0182                               0.0222__________________________________________________________________________CONFIGURATION 3 - 48X MODE DEFLECTION BY GALVO (EQUIV. FOC.LENGTH = 26.967)DIAGRAMLOCATION   8    9    10   11   12   13__________________________________________________________________________GALVO      .5447           1.3617                2.1789                     2.9964                          3.8143                               4.1153ROTATION (°)ANGLE (°)      1.0893           2.7234                4.3578                     5.9928                          7.6286                               8.2306F*THETA    0.5127           1.2818                2.0510                     2.8206                          3.5905                               3.8738ACTUAL RAY HT.      0.5166           1.2905                2.0619                     2.8293                          3.5915                               3.8703DIFFERENCE -0.0039           -0.0087                -0.0181                     -0.0088                          -0.0011                               0.0035RMS OPD    0.0099           0.0066                0.0043                     0.0092                          0.0142                               0.0152__________________________________________________________________________CONFIGURATION 4 - 42X MODE DEFLECTION BY GALVO (EQUIV. FOC.LENGTH = 26.967)DIAGRAMLOCATION   8    9    10   11   12   13__________________________________________________________________________GALVO      .8170           1.6341                2.4514                     3.2690                          4.0871                               4.7035ROTATION (°)ANGLE (°)      1.6340           3.2681                4.9027                     6.5379                          8.1741                               9.4069F*THETA    0.7691           1.5382                2.3075                     3.0771                          3.8472                               4.4274ACTUAL RAY HT.      0.7748           1.5480                2.3182                     3.0840                          3.8442                               4.4122DIFFERENCE -0.0057           -0.0098                -0.0107                     -0.0069                          0.0029                               0.0152RMS OPD    0.0091           0.0052                0.0055                     0.0111                          0.0151                               0.0149__________________________________________________________________________RMS OPD PERFORMANCE FOR BUNDLES ON AXIS AND AT COMPOUND ANGLESENTRANCE PUPIL LOCATION = -70.0; GALVO LOCATION = -24.0.         RAY ANGLE @                  GALVO ROT. IN                              IMAGE PLANE         ENTR. PUPIL                  ORTHOGONAL DIR.                              RAY INTERCEPT__________________________________________________________________________AXIS          0.0000   0.0000      (0.000, 0.000)70% CORN 48X 1ST FMT         5.7614   2.3191      (2.716, 2.177)CORNER 48X 1ST FMT         8.2306   3.3130      (3.858, 3.078)CORNER 48X 2ND FMT         6.6261   4.1153      (3.110, 3.833)70% CORN 42X 1ST FMT         6.5848   2.6373      (3.099, 2.469)CORNER 42X 1ST FMT         9.4069   3.7857      (4.396, 3.496)CORNER 42X 2ND FMT         7.7571   4.7035      (3.629, 4.355)__________________________________________________________________________         DIAGRAM         LOCATION                RMS OPD__________________________________________________________________________AXIS           1     .01070% CORN 48X 1ST FMT         14     .018CORNER 48X 1ST FMT         15     .022CORNER 48X 2ND FMT         16     .01970% CORN 42X 1ST FMT         14     .021CORNER 42X 1ST FMT         15     .017CORNER 42X 2ND FMT         16     .019__________________________________________________________________________  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 9 IN TABLE 10.__________________________________________________________________________ 
    
     The seventh preferred embodiment of the scan lens is a lens system 18f. It is illustrated in FIG. 15. It&#39;s parameters are provided in Table 8. 
     This lens system has a focal length of 54.03 mm, provides 24X coverage and has an F-number F/5.65. 
     The lens system 18f includes 6 lens components C1f-C6f. 
     The first lens component C1f is a negative power lens component. It corresponds to a biconcave lens element E1f. The front surface S1f of the lens component C1f is concave and faces the object side. The rear surface S2f of the lens component C1f is also concave. 
     The second optical component C2f is a positive power lens element E2f. The lens element E2f is a meniscus lens element. It has a front concave surface S3f and a rear (or image side) convex surface S4f. 
     The third optical component C3f is a positive power lens element E3f. The lens element E3f is biconvex. It has a front convex surface S5f and a rear convex surface S6f. 
     The fourth optical component C4f is a positive power lens element E4f. The lens element E4f is a meniscus lens element. It has a front convex surface S7f and a rear (or image side) concave surface S8f. 
     The fifth optical component C5f is a positive power lens element E5f. The lens element E5f is a thick meniscus lens element. It has a front convex surface S9f and a rear (or image side) concave surface S10f. 
     The sixth optical component C6f is a positive power lens element E6f. The lens element E6f is a meniscus lens element. It has a front convex surface S11f and a rear (or image side) concave surface S12f. 
     EXAMPLE 7 
     
                                           TABLE 8__________________________________________________________________________    CLEAR AXIAL         THICK-       V-SURF.    APER. (3)     BEAM  RADIUS  THICKNESS                           INDEX                                NUMBER__________________________________________________________________________    9.56  9.56  DIAPHRAGM                   A1   29.45 9.56  -31.0214                   4.183   1.517                                64.22   33.35 10.03 -104.555                   4.9833   35.64 10.56 -50.6343                   8.949   1.805                                25.44   40.70 11.92 -40.9417                   0.1505   43.44 11.95 534.535 7.250   1.805                                25.46   44.45 12.05 -121.489                   0.2007   44.87 12.02 99.5818 7.250   1.805                                25.48   43.99 11.43 267.602 0.1779   43.16 11.37 40.0994 21.100  1.805                                25.410  30.91 7.36  26.8715 14.05511  30.28 5.64  59.0334 11.526  1.805                                25.412  27.60 4.36  151.299__________________________________________________________________________NOTES:  F/# = 5.65  EF = 54.03FORMATS: 1ST: 15.515 × 12.488 (HOLOGON × GALVO)    2ND: 12.488 × 15.515 (HOLOGON × GALVO)  CONFIGURATION INFORMATION        BESTCFG  BF  FF  FOCUS             A__________________________________________________________________________1    24.581    34.93        -.0162             70.0002    24.581    34.93        -.0162             24.000__________________________________________________________________________N.P.    N.P. X.P. X.P.CFG  LOC.    DIAM.         LOC. DIAM.__________________________________________________________________________1    -70.00    9.56  107.82              14.732    -24.00    9.56 -242.50              47.26__________________________________________________________________________   LENS  STOP REL.                  SEMICFG  EF LENGTH         DIAM.              APER.                  FIELD*__________________________________________________________________________1    54.03   79.823         9.56 5.65                  8.2312    54.03   79.823         9.56 5.65                  8.231__________________________________________________________________________EDGE OF     DEFLECTOR ATCFG  SCAN  FORMAT            ENTRANCE PUPIL__________________________________________________________________________1    7.757 1ST   HOLOGON2    7.757 2ND   GALVO__________________________________________________________________________ *Semi-field angle in scan direction only; maximum semifield angle is a compound angle due to both deflectors operating simultaneously. 
    
     
         3.  CLEAR APERTURES ARE SUFFICIENT TO PASS BUNDLES WITH THE  DIAMETER OF THE ENTRANCE PUPIL CENTERED AROUND SKEW CHIEF  RAYS TERMINATING AT THE CORNERS OF THE 1ST AND 2ND FORMAT.ENTRANCE PUPIL LOCATION = -70; GALVO LOCATION = -24.             GALVO ROT. INCHIEF RAY    RAY ANGLE @             ORTHOGONAL                       IMAGE PLANE                                 DIAGRAMDESCRIPTION    ENTR. PUPIL             DIRECTION RAY INTERCEPT                                 LOCATION__________________________________________________________________________CORNER 42X    8.2306   3.3132    (7.775, 6.201)                                 151ST FMT.CORNER 42X    6.6248   4.1153    (6.266, 7.723)                                 162ND FMT.__________________________________________________________________________  PERFORMANCECONFIGURATION 1 - DEFLECTION BY HOLOGONDIAGRAMLOCATION   2    3    4    5    6    7__________________________________________________________________________ANGLE (DEG.)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306DESIRED RAY HT.      0.5136           2.0543                3.5941                     5.1388                          6.6777                               7.7572ACTUAL RAY HT.      0.5137           2.0547                3.5955                     5.1360                          6.6766                               7.7573DIFFERENCE -0.0001           -0.0004                -0.0014                     0.0028                          0.0010                               -0.0001RMS OPD    0.0167           0.0132                0.0085                     0.0114                          0.0178                               0.0193__________________________________________________________________________CONFIGURATION 2 - DEFLECTION BY GALVO (EQUIV. FOCAL LENGTH = 54.007)DIAGRAMLOCATION   8    9    10   11   12   13__________________________________________________________________________GALVO      0.2723           1.0893                1.9605                     2.7239                          3.5416                               4.1153ROTATION (°)ANGLE (°)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306F*THETA    O.S 133           2.0536                3.5940                     5.1350                          6.6766                               7.7582ACTUAL RAY HT.      0.5135           2.0542                3.5949                     5.1356                          6.6765                               7.7574DIFFERNCE  -0.0002           -0.0007                -0.0008                     -0.0006                          0.0002                               0.0008RMS OPD    0.0168           0.0141                0.0093                     0.0064                          0.0095                               0.0116__________________________________________________________________________RMS OPD PERFORMANCE FOR BUNDLES ON AXIS AND AT COMPOUND ANGLESENTRANCE PUPIL LOCATION = -70.0; GALVO LOCATION = -24.0.        RAY ANGLE @                 GALVO ROT. IN                             IMAGE PLANE        ENTR. PUPIL                 ORTHOGONAL DIR.                             RAY INTERCEPT__________________________________________________________________________AXIS         0.0000   0.0000      (0.000, 0.000)70% CORNER 1ST FMT        5.7614   2.3187      (5.436, 4.356)CORNER 1ST FMT        8.2306   3.3123      (7.775, 6.201)CORNER 2ND FMT        6.6248   4.1153      (6.266, 7.723)__________________________________________________________________________         DIAGRAM         LOCATION                RMS OPD__________________________________________________________________________AXIS           1     .017070% CORNER 1ST FMT         14     .0176CORNER 1ST FMT         15     .0157CORNER 2ND FMT         16     .0235__________________________________________________________________________  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 6 IN TABLE 7.  SF-6 MAY BE SUBSTITUTED FOR SFL-6. ALL GLASSES MUST BE CERTIFIED  ACCEPTABLE REGARDING SAFETY STANDARDS.__________________________________________________________________________ 
    
     The eighth preferred embodiment of the scan lens is a lens system 18g. It is illustrated in FIG. 16. It&#39;s parameters are provided in Table 9. 
     This lens system has a focal length of 54.02 mm, provides 24X coverage and has an F-numbers F/5.65. 
     The lens system 18g includes 6 lens components C1g-C6g. 
     The first lens component C1g is a negative power lens component. It corresponds to a biconcave lens element E1g. The front surface S1g of the lens component C1g is concave and faces the object side. The rear surface S2g of the lens component C1g is also concave. 
     The second optical component C2g is a positive power lens element E2g. The lens element E2g is a meniscus lens element. It has a front concave surface S3g and a rear (or image side) convex surface S4g. 
     The third optical component C3g is a positive power lens element E3g. The lens element E3g is biconvex. It has a front convex surface S5g and a rear convex surface S6g. 
     The fourth optical component C4g is a positive power lens element E4g. The lens element E4g is a meniscus lens element. It has a front convex surface S7g and a rear (or image side) concave surface S8g. 
     The fifth optical component C5g is a positive power lens element E5g. The lens element E5g is a meniscus lens element. It has a front convex surface S9g and a rear (or image side) concave surface S10g. 
     The sixth optical component C6g is a positive power lens element E6g. The lens element E6g is a meniscus lens element. It has a front convex surface S11g and a rear (or image side) concave surface S12g. 
     EXAMPLE 8 
     
                                           TABLE 9__________________________________________________________________________    CLEAR AXIAL        THICK-    V-    SPECIALSURF.    APER. (5)     BEAM RADIUS  NESS INDEX                            NUMBER                                  NOTES__________________________________________________________________________    9.56  9.56 DIAPHRAGM                  A1   29.46 9.56 -31.1064                  4.194                       1.517                            64.2  BK-72   33.34 10.03          -103.666                  4.9863   35.72 10.56          -52.9247                  8.950                       1.834                            37.2  OHARA                                  LASF-0104   40.64 11.89          -41.5045                  0.1505   43.27 11.91          380.484 7.250                       1.834                            37.2  OHARA                                  LASF-0106   44.15 11.95          -146.103                  0.2007   44.47 11.92          104.234 7.250                       1.834                            37.2  OHARA                                  LASF-0108   43.56 11.33          244.357 0.1779   42.83 11.27          40.3800 21.100                       1.834                            37.2  OHARA                                  LASF-01010  30.69 7.30 27.1084 14.05511  30.20 5.60 61.3343 11.530                       1.834                            37.2  OHARA                                  LASF-01012  27.64 4.36 174.548__________________________________________________________________________  F/# = 5.65  EF = 54.02FORMATS: 1ST: 15.515 × 12.488 (HOLOGON × GALVO)    2ND: 12.488 × 15.515 (HOLOGON × GALVO)  CONFIGURATION INFORMATION     BESTCFG   BE  FF FOCUS          A__________________________________________________________________________1  24.562  34.77     -0.0156          70.0002  24.562  34.77     -0.0156          24.000__________________________________________________________________________   N.P.  N.P. X.P. X.P.CFG   LOC.  DIAM.       LOC. DIAM.__________________________________________________________________________1  -70.00  9.56  107.40            14.662  -24.00  9.56 -246.43            47.95__________________________________________________________________________ LENS  STOP REL.                SEMICFG   EE LENGTH       DIAM.            APER.                FIELD*__________________________________________________________________________1  54.02 79.842       9.56 5.65                8.2312  54.02 79.842       9.56 5.65                8.231__________________________________________________________________________   EDGE OF     DEFLECTOR ATCFG   SCAN  FORMAT          ENTRANCE PUPIL__________________________________________________________________________1  7.158 1ST   HOLOGON2  7.758 2ND   GALVO__________________________________________________________________________ *Semi-field angle in scan direction only; maximum semifield angle is a compound angle due to both deflectors operating simultaneously. 
    
     
         3.  CLEAR APERTURES ARE SUFFICIENT TO PASS BUNDLES WITH THE  DIAMETER OF THE ENTRANCE PUPIL CENTERED AROUND SKEW CHIEF  RAYS TERMINATING AT THE CORNERS OF THE 1ST AND 2ND FORMAT.ENTRANCE PUPIL LOCATION = -70; GALVO LOCATION = -24.             GALVO ROT. INCHIEF RAY    RAY ANGLE @             ORTHOGONAL                       IMAGE PLANE                                 DIAGRAMDESCRIPTION    ENTR. PUPIL             DIRECTION RAY INTERCEPT                                 LOCATION__________________________________________________________________________CORNER 42X    8.2306   3.3132    (7.776, 6.202)                                 151ST FMT.CORNER 42X    6.6248   4.1153    (6.267, 7.724)                                 162ND FMT.__________________________________________________________________________  PERFORMANCECONFIGURATION 1 - DEFLECTION BY HOLOGONDIAGRAMLOCATION   2    3    4    5    6    7__________________________________________________________________________ANGLE (DEG.)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306DEIRED RAY HT.      0.5136           2.0543                3.5941                     5.1388                          6.6777                               7.7572ACTUAL RAY HT.      0.5136           2.0544                3.5950                     5.1357                          6.6767                               7.7577DIFFERNCE  -0.0000           -0.0001                -0.0009                     0.0031                          0.0011                               -0.0005RMS OPD    0.0158           0.0123                0.0083                     0.0121                          0.0185                               0.0196__________________________________________________________________________CONFIGURATION 2 - DEFLECTION BY GALVO (EQUIV. FOCAL LENGTH = 54.006)DIAGRAMLOCATION   8    9    10   11   12   13__________________________________________________________________________GALVO      0.2723           1.0893                1.9605                     2.7239                          3.5416                               4.1153ROTATION (°)ANGLE (°)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306F*THETA    0.5133           2.0535                3.5940                     5.1349                          6.6765                               7.7581ACTUAL RAY HT.      0.5134           2.0539                3.5944                     5.1352                          6.6764                               7.7577DIFFERENCE -0.0001           -0.0004                -0.0005                     -0.0003                          0.0001                               0.0004RMS OPD    0.0158           0.0134                0.0089                     0.0062                          0.0090                               0.0111__________________________________________________________________________RMS OPD PERFORMANCE FUR BUNDLES ON AXIS AND AT COMPOUND ANGLESENTRANCE PUPIL LOCATION = -70.0; GALVO LOCATION = -24.0        RAY ANGLE @                 GALVO ROT. IN                             IMAGE PLANE        ENTR. PUPIL                 ORTHOGONAL DIR.                             RAY INTERCEPT__________________________________________________________________________AXIS         0.0000   0.0000      (0.000, 0.000)70% CORNER 1ST FMT        5.7614   2.3187      (5.437, 4.357)CORNER 1ST FMT        8.2306   3.3123      (7.776, 6.202)CORNER 2ND FMT        6.6248   4.1153      (6.267, 7.724)__________________________________________________________________________        DIAGRAM        LOCATION               RMS OPD__________________________________________________________________________AXIS          1     .016070% CORNER 1ST FMT        14     .0183CORNER 1ST FMT        15     .0155CORNER 2ND FMT        16     .0238__________________________________________________________________________  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 6 IN TABLE 7.  CONTACT DESIGN DEPARTMENT BEFORE SUBSTITUTING GLASSES. ALL  GLASSES MUST BE CERTIFIED ACCEPTABLE REGARDING SAFETY  STANDARDS.__________________________________________________________________________ 
    
     The parameters for the last three embodiments, Examples 9, 10 and 11, correspond to lens systems 18H, 18i and 18j. They are illustrated in FIGS. 17, 18, and 19 and their parameters are provided below in Tables 10, 11 and 12, respectively. 
     EXAMPLE 9 
     
                                           TABLE 10__________________________________________________________________________    CLEAR AXIAL        THICK-    V-    SPECIALSURF.    APER. BEAM RADIUS  NESS INDEX                            NUMBER                                  NOTES__________________________________________________________________________    9.56  9.56 DIAPHRAGM                  A1   31.20 9.56 -28.3964                  9.753                       1.517                            64.2- BK-72   41.72 10.75          112.662 8.2233   49.99 12.57          -631.554                  14.591                       1.805                            25.4  SFL-64   56.75 14.49          -72.1304                  0.1505   62.20 14.54          184.339 10.000                       1.805                            25.4  SFL-66   62.68 14.63          -108.480                  0.2007   60.41 14.54          55.3311 9.000                       1.805                            25.4  SFL-68   57.48 13.07          93.2760 0.1509   52.50 12.97          34.2902 24.870                       1.805                            25.4  SFL-610  27.37 6.19 16.9223 4.68811  26.42 5.27 22.3953 9.000                       1.805                            25.4  SFL-612  21.64 3.35 75.2922__________________________________________________________________________NOTES:  F/# = 2.84  EF = 27.17FORMATS: 1ST FORMAT OF 48X MODE: 7.756 × 6.244 (HOE × GALVO)    2ND FORMAT OF 48X MODE: 6.244 × 7.756 (HOE × GALVO)    1ST FORMAT OF 42X MODE: 8.866 × 7.136 (HOE × GALVO)    2ND FORMAT OF 42X MODE: 7.136 × 8.866 (HOE × GALVO)  CONFIGURATION INFORMATION     BESTCFG   BE  FF FOCUS          A__________________________________________________________________________1  9.3760  2.59     -.0009          70.0002  9.3760  2.59     -.0009          70.0003  9.3760  2.59     -.0009          24.0004  9.3760  2.59     -.0009          24.000__________________________________________________________________________   N.P.  N.P. X.P.           X.P.CFG   LOC.  DIAM.       LOC.           DIAM.__________________________________________________________________________1  -70.00  9.56 20.31            3.852  -70.00  9.56 20.31            3.853  -24.00  9.56 43.80           12.124  -24.00  9.56 43.80           12.12__________________________________________________________________________ LENS  STOP REL.                SEMICFG   EF LENGTH       DIAM.            APER.                FIELD__________________________________________________________________________1  27.15 90.625       9.56 2.84                8.231°2  27.15 90.625       9.56 2.84                9.407°3  27.15 90.625       9.56 2.84                8.231°4  27.15 90.625       9.56 2.84                9.407°__________________________________________________________________________   SEMI           DEFLECTOR ATCFG   DRAG  MODE FORMAT             ENTRANCE PUPIL__________________________________________________________________________1  3.879  48X  1ST   HOLOGON2  4.432  42X  1ST   HOLOGON3  3.879  48X  2ND   GALVO4  4.432  42X  2ND   GALVO__________________________________________________________________________  PERFORMANCECONFIGURATION 1ANGLE (DEG.)      1.0893           2.7234                4.3578                     5.9928                          7.6286                               8.2306DESIRED RAY HT.      0.5136           1.2840                2.0544                     2.8245                          3.5941                               3.8786ACTUAL RAY HT.      0.5161           1.2894                2.0606                     2.8288                          3.5929                               3.8729DIFFERENCE -0.0025           -0.0054                -0.0063                     -0.0043                          0.0012                               0.0057RMS OPD    0.0078           0.0072                0.0068                     0.0052                          0.0061                               0.0086__________________________________________________________________________CONFIGURATION 2ANGLE (DEG.)      1.6340           3.2681                4.9027                     6.5379                          8.1741                               9.4069DESIRED RAY HT.      0.7705           1.5411                2.3116                     3.0810                          3.8532                               4.4323ACTUAL RAY HT.      0.7740           1.5467                2.3171                     3.0840                          3.8467                               4.4180DIFFERNCE  -0.0035           -0.0057                -0.0055                     -0.0029                          0.0065                               0.0143RMS OPD    0.0073           0.0071                0.0064                     0.0047                          0.0083                               0.0179__________________________________________________________________________CONFIGURATION 3 (EQUIV. FOCAL LENGTH = 27.005)ANGLE (DEG.)      1.0893           2.7234                4.3578                     5.9928                          7.6286                               8.2306F*THETA    0.5134           1.2836                2.0539                     3.8246                          3.5955                               4.8793ACTUAL RAY HT.      0.5160           1.2893                2.0606                     2.8288                          3.5929                               3.8729DIFFERENCE 0.0026           057  0.0067                     0.0042                          -0.0026                               -0.0064RMS OPD    0.0066           0.0030                0.0034                     0.0083                          0.0102                               0.0105__________________________________________________________________________CONFIGURATION 4 (EQUIV. FOCAL LENGTH = 26.974)ANGLE (°)      1.6340           3.2681                4.9027                     6.5379                          8.1741                               9.4069F*THETA    0.7693           1.5386                2.3081                     3.0780                          3.8483                               4.4287ACTUAL RAY HT.      0.7740           1.5467                2.3170                     3.0840                          3.8466                               4.4177DIFFERENCE 0.0047           0.0081                0.0089                     0.0060                          -0.0017                               -0.0110RMS OPD    0.0057           0.0017                0.0052                     0.0093                          0.0105                               0.0158__________________________________________________________________________  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 10 IN TABLE 11.  SF-6 MAY BE SUBSTITUTED FOR SFL-6 IF DESIRED.__________________________________________________________________________ 
    
     EXAMPLE 10 
     
                                           TABLE 11__________________________________________________________________________    CLEAR    AXIAL        THICK-     V-SURF.    APER.    BEAM RADIUS  NESS INDEX NUMBER                                  GLASS__________________________________________________________________________    9.56 9.56 DIAPHRAGM                 A1   28.91    9.56 -35.1825                 4.000                      1.517 64.2  BK-72   33.12    9.98 92.6682 5.0053   35.53    10.92         -128.298                 9.000                      1.805 25.4  SFL-64   39.72    12.21         -50.1277                 0.6425   43.71    12.29         94.2570 9.000                      1.805 25.4  SFL-66   44.08    12.12         -184.339                 0.1777   43.50    12.05         34.5115 18.000                      1.847 23.8  SFL-578   31.82    8.33 24.4424 7.9629   31.83    7.61 186.648 6.124                      1.517 64.2  BK-710  31.64    7.15 -60.0977__________________________________________________________________________NOTES:  F/# = 5.64  EF = 53.95FORMATS: 1ST FORMAT: 15.515 × 12.488 (HOLOGON × GALVO)    2ND FORMAT: 12.488 × 15.515 (HOLOGON × GALVO)  CONFIGURATION INFORMATION     BESTCFG   BF  EE FOCUS          A__________________________________________________________________________1  40.1107  31.52     -.02110          70.0002  40.1107  31.52     -.02100          24.000__________________________________________________________________________   N.P.  N.P. X.P. X.P.CFG   LOC.  DIAM.       LOC. DIAM.__________________________________________________________________________1  -70.00  9.56  115.75            13.402  -24.00  9.56 -346.97            68.60__________________________________________________________________________ LENS  STOP REL.CFG   EF LENGTH       DIAM.            APER.__________________________________________________________________________1  53.95 59.910       9.56.            5.642  53.95 59.910       9.56 5.64__________________________________________________________________________   SEMI SEMI      DEFLECTOR ATCFG   FIELD   DRAG       FORMAT             ENTRANCE PUPIL__________________________________________________________________________1  8.231   7.757       1ST   HOLOGON2  8.231   7.673       2ND   GALVO__________________________________________________________________________  PERFORMANCECONFIGURATION 1ANGLE (DEG.)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306DESIRED RAY HT.      0.5136           2.0543                3.5941                     5.1388                          6.6777                               7.7572ACTUAL RAY HT.      0.5129           2.0519                3.5913                     5.1321                          6.6764                               7.7633DIFFERNCE  0.0006           0.0024                0.0028                     0.0067                          0.0012                               -0.0062RMS OPD    0.0228           0.0144                0.0170                     0.0212                          0.0096                               0.0232__________________________________________________________________________CONFIGURATION 2 (EQUIV. FOCAL LENGTH = 54.0110)ANGLE (DEG.)      0.5446           2.1786                3.8129                     5.4477                          7.0832                               8.2306F*THETA    0.5134           2.0537                3.5943                     5.1354                          6.6771                               7.7587ACTUAL RAY HT.      0.5128           2.0515                3.5911                     5.1326                          6.6771                               7.7627DIFFERENCE -0.0006           -0.0022                -0.0032                     -0.0028                          -0.0000                               0.0040RMS OPD    0.0232           0.0184                0.0096                     0.0035                          0.0075                               0.0138__________________________________________________________________________  THE DISTANCE(S) FROM THE ENTRANCE PUPIL(S) TO THE IMAGE PLANE  OF THIS DESIGN MATCHES THE CORRESPONDING DISTANCE(S) OF  EXAMPLE 9 IN TABLE 10.  SF-6 AND SF-57 MAY BE SUBSTITUTED FOR SFL-6 AND SFL-57 IF__________________________________________________________________________  DESIRED. 
    
     EXAMPLE 11 
     
                                           TABLE 12__________________________________________________________________________    CLEAR    AXIAL        THICK-     V-SURF.    APER.    BEAM RADIUS  NESS INDEX NUMBER                                  GLASS__________________________________________________________________________    9.14 9.14 DIAPHRAGM                 71.0001   28.68    9.14 -23.4834                 15.885                      1.547 53.6  BALF-52   43.74    11.42         287.364 5.3893   49.84    12.69         PLANO   10.916                      1.805 25.4  SF-64   52.67    14.07         -56.0766                 10.0085   58.31    14.44         -1464.21                 9.000                      1.805 25.4  SF-66   59.32    14.65         -100.678                 0.2007   58.06    14.59         70.0432 8.947                      1.805 25.4  SF-68   55.62    13.42         144.437 9.8099   48.35    11.76         44.5149 46.000                      1.805 25.4  SF-610  15.32    2.15 45.7245__________________________________________________________________________NOTES:F/# = 2.95EF = 26.98PERFORMANCEANGLE (DEG.)      1.6340           3.2681                4.9027                     6.5379                          8.1741                               8.4079DESIRED RAY HT.      .7656           1.5311                2.2966                     3.0621                          3.8277                               3.9370ACTUAL RAY HT.      .7688           1.5363                2.3019                     3.0647                          3.8242                               3.9324DIFFERNCE  -0.0032           -0.0052                -0.0053                     -0.0026                          +0.0035                               +0.0046P-V OPD    .042 .045 .058 .066 .085 .093__________________________________________________________________________IMAGE ANGULAR        APPROX. REL                  MAX. APER. WITHHEIGHT FIELD  ILLUM. (IMAGE)                  NO VIGNETTING__________________________________________________________________________1.38  2.94   1.00      F/3.02.76  5.89   1.01      F/3.03.93  8.41   1.03      F/3.0__________________________________________________________________________PUPIL    LOCATION      DIAMETER__________________________________________________________________________Ent.    -71.00 9.14Exit    16.87  3.60__________________________________________________________________________ 
    
     The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, other types of diffractive surfaces can be substituted for the holographic surface of a deflector. The deflectors may be switched in their positions, other types of dual deflector systems may be used and one or more aspheric or diffractive surfaces may be added to a scan lens system.