INTEGRATED OPTICAL SYSTEM FOR ENDOSCOPES AND THE LIKE

Abstract: Optical systems (1-19) for endoscopes and the like are characterized by an integrated design in which the locations of the components and the aberration corrections are no longer tied to the optical functions of the objective (1-6) and the relays (7-19), and in which the relays may depart from symmetry. The power requirements can thus be shifted from one group to another, thereby reducing the overall power requirement. Moreover, the aberration correction can be shared between the optical groups of the integrated system.

Description: INTEGRATED OPTICAL SYSTEM FOR ENDOSCOPES AND THE LIKE Field of the Invention The present invention relates generally to optical lens systems, and more particularly, to lens systems suitable for endoscopes and the like. Background of the Invention In endoscopy and related fields, such as borescopes and dental scopes, the complete optical system is thought of as consisting of four basic and separate optical functions. Those functions are, in sequence of the direction of the travelling light, as follows: (1 ) an objective which forms the first image of an object under surveillance, (2) a field lens which images the pupil of the objective onto the next image transfer lens, (3) an image transfer lens which reimages the first image onto the next field lens. The pupil and image transfer steps are repeated as often as is needed to obtain a desired tube length, and (4) a focusing lens which presents the final image to a sensor, such as a person's eye, a CCD camera, or a photographic film. This approach is the classical approach, which is appropriate for the following reasons: (1) The design of the optical system is broken up into parts with single and clearly defined and separate functions, functions to each of which an optical designer may bring considerable experience. (2) The light transfer capacity and information transfer capacity of an endoscope is at a maximum when the optical power is concentrated at the image planes and pupil planes. The expedience of this approach is brought out by numerous U.S. patents on endoscopes which treat the objective, the relay system, and the eyepiece as separate parts of the total system. The disadvantage of treating the different optical components as separate entities is that the distribution of the optical power is very uneven and that certain aberrations are naturally at a maximum, like astigmatism, field curvature, and chromatic aberrations. The correction of these aberrations requires relatively short radii of curvature. These short radii of curvature are difficult to fabricate, require tight tolerances, and they are therefore the main contributors to the considerable cost of the fabrication of an endoscope. A truly inexpensive endoscope, sufficiently inexpensive to be offered as a disposable item, is presently not practical with conventional designs. Summary of the Invention Several exemplary embodiments of the present invention are disclosed which provide an integrated optical system suitable for endoscopes, borescopes, dental scopes, and the like. One aspect of the present invention is an endoscope having a reduced number of elements compared with conventional endoscopes. The elements may advantageously have relatively long radii of curvature which facilitates their mass production. Furthermore, the elements are not necessarily of a meniscus shape. Some of the exemplary embodiments have an outside entrance pupil location (i.e., the pupil is located between the embodiment and the object to be imaged), so that they are suitable for a tapered probe (e.g., for concealment) or for accommodating a liπe-of-sight deviating prism on the image side of the pupil location. Other embodiments include or may be combined with a field expander, in which the pupil location may be located so as to accommodate a liπe-of-sight deviating prism. Further, many of the embodiments disclosed herein are highly insensitive to tilt and decentration of their components. In several of the exemplary embodiments herein, the foregoing advantages are achieved in a lens system characterized by an integrated design in which the locations of the components may not be dictated by the optical functions of the objective and the relays. Further, the aberration correction may be advantageously distributed over two or more groups, thereby providing relief to the first group (which conventionally has the highest optical power and is in need of most of the aberration correction) and permitting the radii of curvature of the optical components to be reduced, resulting in a smaller overall power requirement (i.e., the sum of the absolute values of the powers of the optical components is smaller). In several of the exemplary embodiments disclosed herein, departure from symmetry of the relay system is employed to further the integration. It has been found that this integration of the optical functions and the aberration correction, as well as the departure from symmetry, may be very beneficial in that they greatly simplify the optical system by reducing its curviness and complexity. The resulting simplicity of the optical system results in reduced costs and may permit it to be used as a disposable item. In some embodiments described herein, a plano-convex lens or a double convex lens can be corrected for astigmatism since such a lens is displaced from the stop location. In this way, optical surfaces of very short radii of curvature may not be needed to correct the astigmatism of the total optical system. Furthermore, the spherical aberration of convex-piano lenses used in several of the embodiments herein is greatly reduced and may approach the minimum possible for a single element. In many of the embodiments herein, the chromatic aberrations may be greatly reduced compared to many conventional systems. For example, chromatic aberrations may be reduced by a factor of 2 to 4 without the presence of a chromatic aberration reducing element. Thus, in some embodiments further color correction may not be necessary. In one embodiment, a color corrected optical endoscope system, including a plurality of elements, in accordance with the present invention comprises an objective element and relay system providing substantially all color correction for the endoscope system using at least one curved optical interface providing color correction, the objective element and the relay system optically aligned to transfer an image from an input plane of the objective element to an output plane of the endoscope system, each of the plurality of optical elements being uniformly refractive and suitable for use with at least one of the e, FN, and CN spectral lines. Other embodiments are disclosed herein which include several transfers and can be basically fully color corrected by the use of a single color correcting element of modest optical power. Optical distortion of many kinds, which may be very high in the objective, can be corrected at more convenient and effective places, resulting in a single integrated system of greatly reduced complexity. Additional optics, like a close-up lens, a field expander, a field flattening lens, or additional relay groups, may be employed with several of the inventive embodiments disclosed herein. Yet another embodiment of the present invention is a color corrected optical endoscope system including an optical system having a plurality of optical elements, comprising an objective element and a first relay system having a first number of curved surfaces, the first relay system including an optical interface having a curvature that provides substantially all of the color correction for the endoscope system, the objective element and the first relay system optically aligned to transfer an image from an input plane of the objective element to an output plane of the endoscope system, wherein the plurality of optical elements are suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line. Another embodiment of the present invention is a color corrected optical endoscope including a plurality of optical elements, comprising an objective and a relay system, the relay system having at least one optical interface providing color correction for the endoscope, the objective providing substantially no color correction, the objective and the relay system aligned along a common optical axis, and the plurality of optical elements being suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line. Still another embodiment of the present invention is a color corrected endoscopic imaging system including a plurality of optical elements, comprising an objective for imaging an object onto a focal plane and at least one relay that is optically aligned with the objective along a common optical axis, the relay including curved surfaces, at least one curved interface providing color correction for the endoscopic imaging system, wherein the number of the curved surfaces in the relay is not greater than 5. Yet another embodiment of the present invention is a color corrected imaging system for use with an endoscope and including a plurality of optical elements, comprising an objective having an optical axis and at least one relay aligned with the objective along the optical axis, the objective having not more than 3 curved surfaces, at least one of the optical elements providing color correction for the imaging system. Another embodiment of the present invention is a color corrected endoscope including a plurality of optical elements, the endoscope comprising an objective system and at least three relay systems optically aligned with the objective system, wherein the objective system and three of the at least three relay systems together include not more than 13 curved surfaces. Another embodiment of the present invention is a color corrected endoscope including a plurality of optical elements, the endoscope comprising an objective system and at least two relay systems including optical elements, the at least two relay systems optically aligned with the objective system, wherein the objective system and two of the at least two relay systems together include not more than 10 curved surfaces, the optical elements suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line, and at least one of the optical elements providing color correction to the endoscope. Another embodiment of the present invention is a color corrected endoscope, including a plurality of lens elements, comprising an objective and at least one relay, wherein one of the at least one relay includes not more than 3 lens elements, the objective and the at least one relay aligned to transfer an image from an input plane of the objective to an output plane of the endoscope, at least one of the lens elements providing color correction to the endoscope. Another embodiment of the present invention is a color corrected endoscopic system including a plurality of optical elements, comprising an objective group and at least two relay groups aligned with the objective group along an optical axis, one of the relay groups including no optical elements of negative optical power, and another of the relay groups providing color correction to the endoscopic system. Another embodiment of the present invention is a color corrected endoscopic system including a plurality of optical elements, comprising an objective and at least one relay group aligned with the objective along an optical axis, the objective and the at least one relay group together including not more than 2 elements of negative optical power, at least one of the plurality of optical elements providing color correction for the endoscopic system. Another embodiment of the present invention is a color corrected optical endoscope including a plurality of optical elements, comprising means for forming a first image of an object and means for relaying the first image and forming a second image, wherein the relaying means includes means for correcting chromatic aberrations, whereas the means for forming a first image includes substantially no means for correcting chromatic aberrations, the means for forming a first image and the relaying means being aligned along a common optical axis, the plurality of optical elements being suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line. Another embodiment of the present invention is an optical system including a plurality of optical elements, comprising an objective a color-correcting relay providing substantially all color correction for the system using at least one curved interface providing color correction and a non-color correcting relay, wherein the non-color correcting relay, the objective, and the color-correcting relay are aligned along a common optical axis and optically aligned to transfer an image from an input plane of the objective to an output plane of the optical system, in which each of the plurality of optical elements is uniformly refractive and suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line. Another embodiment of the present invention is a method of imaging an object, comprising forming a first image of the object with a non-color correcting objective system providing at least a first and a second relay system, aligning the objective system and the first and second relay systems along a common optical axis, receiving the first image from the objective system with the first relay system to form a second image, transferring the second image from the first relay system using the second relay system to form a third image of the object and correcting chromatic aberrations with one of the relay systems by using at least one optical interface, wherein the objective system and the plurality of relay systems are suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line. Another embodiment of the present invention is a method of imaging an object, comprising providing an objective for forming a first image of the object, providing at least three relay systems optically aligned with the objective system, wherein the objective and the relay systems together include not more than 13 curved surfaces, the objective and the relay systems being suitable for use with at least a portion of the spectrum extending from the FN to the CN spectral line, receiving the first image with one of the relay systems, forming an output image with another of the relay systems, in which the output image can be received by a viewer and providing color correction to the output image with at least one curved interface. Another embodiment of the present invention is a method of designing an integrated aberration corrected endoscope, comprising providing a plurality of optical groups, wherein the groups are aligned along a common optical axis and each of the groups produces a respective image at a respective focal plane, the groups including an objective and at least one relay and providing a first one of the groups with more aberration correction than the first group requires to be aberration corrected, and providing a second one of the groups with less aberration correction than the second group requires to be aberration corrected, wherein the aberration correction of the first group compensates for lack of aberration correction in the second group to produce an aberration corrected endoscope. Another embodiment of the present invention is an integrated aberration corrected endoscope, comprising a first optical group, the first group having more aberration correction than the first group requires to be aberration corrected and at least a second optical group, the second group having less aberration correction than the second group requires to be aberration corrected, in which the aberration correction of the first group compensates for lack of aberration correction in the second group to produce the integrated aberration corrected endoscope, wherein the groups are aligned along a common optical axis and each of the groups produces a respective image at a respective focal plane, the groups including an objective and at least one relay. Another embodiment of the present invention is an optical system for transferring an image from a first plane to a second plane via an intermediate plane, comprising an objective comprising at least one optical element disposed between the first plane and the intermediate plane for forming a relatively uncorrected image at the intermediate plane and a relay comprising at least one optical element disposed between the intermediate plane and the second plane for forming a relatively more corrected image at the second plane. Brief Description of the Drawings Figure 1 is an optical schematic view of an endoscope constructed in accordance with a conventional layout in which each component has a single function in the system. Figure 2 is an optical schematic view of a first embodiment of the present invention in which the entrance pupil is located outside the first group by a relatively small distance. Figure 3 is an optical schematic view of a second embodiment of the present invention in which full advantage of the power reduction and aberration reduction is taken by locating the entrance pupil outside the first group by a large distance. Figure 4 is an optical schematic view of a third embodiment of the present invention which incorporates a rod- shaped element. Figure 5 is an optical schematic view of a fourth embodiment of the present invention which is made of all glass elements and which incorporates a single negative element that provides chromatic aberration correction for the illustrated system. Figure 6 is an optical schematic view of a fifth embodiment of the present invention which is a simple glass and plastic system that basically fully corrects for chromatic aberrations. Figure 7 is an optical schematic view of a sixth embodiment of the present invention in which the three basic groups have been augmented with an element near the focal plane of the first group. Figure 8 is an optical schematic view of a seventh embodiment of the present invention in which a fourth group (IV) of low optical power has been added near the focal plane of the first group (F), the fourth group containing a single negative element for correcting the chromatic aberrations. Figure 9 is an optical schematic view of an eighth embodiment of the present invention which incorporates a meniscus shaped element. Figure 10 is an optical schematic view of a ninth embodiment of the present invention which incorporates a second image relay and basically fully corrects for chromatic aberrations with a single element of negative optical power. Figure 11 is an optical schematic view of a tenth embodiment of the present invention which incorporates a third image relay while still basically fully correcting for chromatic aberrations using only one element of negative optical power. Figures 12A-12C provide an optical schematic view of an eleventh embodiment of the present invention which includes three image relays, with the color correction basically being performed by a single element in the first optical relay. Figure 12D is an enlarged view of the objective of Figure 12A. Figures 13A-13C provide an optical schematic view of a twelfth embodiment of the present invention which includes three image relays, with the color correction basically being performed by a single element in the second optical relay. Figure 13D is an enlarged view of the objective of Figure 13A. Figures 14A-14C provide an optical schematic view of a thirteenth embodiment of the present invention which includes three image relays, with the color correction basically being performed by a single element in the third optical relay. Figure 14D is an enlarged view of the objective of Figure 14A. Figures 15A-15C provide an optical schematic view of a fourteenth embodiment of the present invention which includes three image relays but has only nine optical elements with optical power. Figure 15D is an enlarged view of the objective of Figure 15A. Figures 16A-16C provide an optical schematic view of a fifteenth embodiment of the present invention which includes three image relays that comprise plastic elements. Figure 16D is an enlarged view of the objective of Figure 16A. Figures 17A-17C provide an optical schematic view of a sixteenth embodiment of the present invention which includes three image relays that comprise glass molded elements. Figure 17D is an enlarged view of the objective of Figure 17A. Figures 18A-18C provide an optical schematic view of a seventeenth embodiment of the present invention which includes three image relays, in which plano-plano interfaces divide the image relays into segments so that the endoscope is less susceptible to breakage when bent. Figure 18D is an enlarged view of the objective of Figure 18A. Detailed Description of the Preferred Embodiments Exemplary embodiments 1-11, corresponding to Figures 2-12 described below, are standardized such that the objective and the first relay have a length of about 100 millimeters, and most have a nominal magnification of unity. In this way, the performance of Embodiments 1-11 can be conveniently compared. Embodiments with other magnifications, fields of view, numerical apertures, and with additional relays are presented in order to show that the general concept of the invention is effective over a wide range of applications. The embodiments described herein (1-18) use conventional, non- GRIN (gradient refractive index) lens elements, and thus each lens has a uniform refractive index, though other lens types may be used as well. in Figures 1-18, the object and image planes are indicated by an 'Obj' and 'lm,' respectively. Intermediate focal planes and pupil planes are indicated at various points in the optical train by an 'F' and a 'P in ,', respectively. Optical system features of the object plane ("surface 0" in Figures 1-18), the first pupil plane (or stop, corresponding to "surface 1" in Figures 1-11 and "surface 4" in Figures 12-18), lens surfaces, and the final image plane are numbered sequentially. Note that in Figures 1-11, the entrance pupil P ent and the stop are coincident, though in other embodiments, they may be displaced from one another. The propagation of marginal and chief rays is indicated throughout the figures with hashed lines. Tables 1-18 present the construction parameters of the embodiments illustrated in Figures 1-18. Table 1 refers to the system shown in Figure 1, Table 2 to the system of Figure 2, and so on for the other tables and figures. The first column indicates the surface number ("SURF") shown in the figures, the second column indicates the radius of curvature ("RD") of the surface, and the third column indicates the axial separations ("TH"). The optical component materials ("MEDIUM") are presented in the fourth column. As is customary, air is the implied medium of propagation when no medium is explicitly indicated. The fifth column provides the diameters ("DIAMETER") of the respective components, object, pupil, or image. With respect to Embodiments 12-18, the clear aperture is advantageously limited to a diameter of 2.5 mm, as indicated in Table 20, though in other embodiments the clear aperture may be greater. The aspheric data are presented in the sixth column. The conic constant ("CC") is defined and discussed below in connection with equation (1). The surface and plane numbers in Tables 1-18 refer to those in the figures. The refractive indices (with respect to the e, F , and C spectral lines), the dispersion, and the preferred manufacturers of the various optical component materials disclosed herein are presented in Table 19. Optical performance parameters for Embodiments 1-18 are indicated in Table 20. Figure 1 is an optical schematic of an endoscope system which is constructed in accordance with the classical, conventional, concept of separation of the various functions. Group I is an objective which contains the entrance pupil plane (P ent ), while Group II represents a field lens which is located at the focal plane of the objective (F). Group III represents a transfer lens which transfers the image formed by the objective onto a subsequent focal plane (here, the image plane, Im). All groups are located at pupil planes or focal planes. It is apparent from Figure 1, as well as from the radii of curvature data of Table 20, that the distribution of optical power is very uneven. The value of the sum of the absolute values of the curvatures, which is a measure of difficulty of fabrication, is 1.62/mm (see column 5 of Table 20) for this prior art embodiment, which is uncorrected for chromatic aberrations. If this embodiment were corrected for chromatic aberrations, the sum of the absolute values of the curvatures would more than double. This would be disadvantageous, since, in general, the greater the sum of the absolute values of the curvatures, the higher the manufacturing costs. The pertinent performance data are listed in Table 20, and the construction parameters are listed in Table 1. Figure 2 illustrates one embodiment of the present invention, which is an endoscope using a very small number of components. This design shows that by allowing the locations of the pupils and the intermediate image to depart modestly from their classical positions (cf. Figure 1), the sum of the absolute values of the curvatures (SC) can be reduced to 1.15|mm (from 1.62/mm as in Embodiment 1-see Table 20) while still improving optical performance (e.g., the peak to valley wavefront distortion is only 0.32 waves, compared with 0.79 waves in Embodiment 1-see Table 20). Only three plastic elements having a nonmeniscus shape and devoid of steep curves are needed to provide diffraction-limited performance for the monochromatic aberrations. A cone-shaped tip can be included in many applications, such as those which do not have a line-of-sight deviating prism. Such a tip may be advantageously used as a probe to reduce any disturbances to the object being examined or to reduce the exposure of the embodiment itself. The pertinent performance data are listed in Table 20, and the construction parameters are listed in Table 2. Figure 3 is an optical schematic of another embodiment of the present invention. This endoscope also uses few components and is simple in construction, but is nevertheless highly corrected for aberrations, including chromatic aberrations, with the maximum axial chromatic (wavefront) aberration being only 0.21 waves (see column 23 of Table 20). Although no negative element has been added to correct chromatic aberrations, the axial chromatic aberration is more than a factor four smaller than in the classical layout (0.90 waves, cf. Fig. 1 and Table' 20) and is within the diffraction limit. Thus, this example shows the advantage of a redistribution of power, which in this example is related to the attendant shift of pupil (Pin t ). While Embodiment 3 departs even further from the classical layout than does Embodiment 2, the SC is only 0.55, and the peak-to-valley wavefront aberration has been reduced to 0.21 waves (see Table 20). Figure 4 is an optical schematic of an endoscope which consists of two components. The second and third groups II, III are cemented to a rod-shaped element, so that there are only four glass/air surfaces. Despite the relatively few elements of this embodiment, aberrations are at the diffraction limit. For example, the peak-to-valley wavefront aberration is only 0.27 waves, and the maximum axial chromatic aberration is only 0.31 waves, as indicated in Table 20. This example shows that rod-shaped elements can be beneficially employed in the present invention. The advantage of using a rod-shaped element is that the optical distance from the object to the image plane is increased without increasing the diameter of the optical system. This embodiment also demonstrates that rod-shaped elements may alter the location of the intermediate pupil plane (P and focal plane of the objective (F), which have now moved beyond the third (III) and second (II) groups, respectively. A shorter rod-shaped element can put the intermediate focal and pupil planes (F and P r at the second (II) or third (III) element if so desired. While some of the embodiments of the present invention do not require meniscus-shaped optical elements, their incorporation is not precluded, as is shown in this example. The gain in using meniscus shapes, however, may be modest. Figure 5 is an optical schematic of an endoscope which is constructed entirely of glass elements, none of which is meniscus-shaped. In other embodiments, plastic lenses may be used in addition to or in place of the glass elements, as illustrated in other exemplary embodiments. The curvatures are shallow and spherical, with all but one of the surfaces having radii of curvature greater than 8 mm. The first group I easily provides the needed space for a line-of-sight deviation prism (which includes surfaces 2 and 3) between the entrance pupil P Elrt and the first group (I), even though the field of view is relatively large (70 degrees). It is important to note that, despite the fact that the first group (I) is not color corrected in any way, the chromatic aberration of the whole system is basically fully corrected (the maximum axial chromatic aberration is only 0.12 waves-see Table 20) at surface 10 by means of a single negative element, although additional color correction can be provided, and additional negative elements can be used. The three groups (I, II, 111) are fully integrated but are far removed from the objective focal plane (F) and the intermediate pupil plane (P . Figure 6 is an optical schematic of an endoscope which is constructed partly of glass and partly of plastic, demonstrating how lenses of different materials can be combined in a single endoscope. Again, no steep curves or meniscus elements are needed to achieve the relatively high numerical aperture (N.A.) of 0.025, although such elements may be used. The distortion is well corrected, with the maximum image distortion being only -3% (see Table 20). The object has been set at infinite distance to show that the basic design is not affected by a change in magnification as is generally the case with endoscopes. The color correction is basically provided by surface 6. Figure 7 is an endoscope to which an additional group of optical power (IV) has been added, resulting in a modestly improved monochromatic performance. The added element IV is positioned close to the image plane (F) of the objective where element IV is most effective. The relatively weak power of element IV (which is positive) shows that most of the burden of the optical functions, as well as the aberration corrections, are performed by the groups I, II, and III, which are displaced from the image planes and pupil planes. This example shows that an additional element near an image plane or a pupil plane can be used with the present invention. Figure 8 is a highly corrected endoscope using plastic elements with a relatively high N.A. of 0.025. Only one of the elements, element IV, is preferably positioned close to an image or pupil plane but is again of low optical power. Although four optical elements are used, the SC is still only 1.06 and the maximum axial chromatic aberration is only 0.31 waves. The color correction is basically provided by surface 8. Figure 9 is an endoscope similar to the one shown in Figure 8. The magnification has been increased to 2X, showing that the design remains very similar to the 1X and OX designs, as is generally the case with endoscopes. Again, a meniscus element has been employed to show that despite the fact that the present invention can be used with nonmeniscus elements, their employment is by no means excluded. In this embodiment, the fourth group (IV, the meniscus element) is of negative power, again showing that the fourth element is a nonessential addition to the other three groups of the invention. The color correction is basically provided by surface 9. Figure 10 is an endoscope in which a second relay (designated as group IV) is used. This embodiment has a very large field of view of 80 degrees and a relatively high N.A. of 0.025. Despite these large values, a deviation prism (which includes surfaces 2 and 3) can be readily accommodated between the objective (I) and the entrance pupil (P ent ), as shown in Figure 10. The total system is still very well corrected at surface 10 by a single color correcting element of low power, which basically provides full correction of the chromatic aberrations, e.g., the maximum axial chromatic aberration is only 0.35 waves (see Table 20). As the first three groups (I, II, III) are together fully correctable, the addition of classical relays to those first three groups is not excluded. Figure 11 shows an endoscope having three image relays that is still very well corrected, with a maximum axial chromatic aberration of only 0.04 waves (see Table 20). Again, the chromatic aberrations are basically fully corrected at surface 10 with a single element of negative optical power, though additional elements may be used. In other embodiments, additional color correcting elements may be required. In Figure 11 the optical power of the color correcting element, even though it provides basically the full color correction, approaches a value comparable to those of the other components. In particular, surfaces 9 and 10 have radii of curvature of 50 mm and 4.5 mm, respectively. The elements are of glass, and no aspheric surfaces are employed. Figures 12-18, corresponding to Tables 12-18, show exemplary embodiments of the present invention in which a field expander (corresponding to surfaces 1-2 in each of Figures 12-18) has been included in or with the objective (corresponding to surfaces 1-6 in each of Figures 12-18). In these embodiments, the field expander permits a large field of view (110 degrees) to be imaged and may also correct for the field curvature (with the Petzvalsu being correspondingly smaller). Embodiments 12-18 include a 3 relay system, with the lengths indicated in Tables 12-18 corresponding to a system that can be used in medical applications. In Embodiments 12-18, a single color correcting element basically provides all the color correction. Figures 12A-D illustrate an embodiment which has only 9 lens elements, 12 curved surfaces, and a sum of the absolute values of the curvatures of the optical elements equal to 3.65/mm (see Table 20). These values represent a significant improvement as compared with conventional systems, which may contain 30-35 optical elements and have a correspondingly higher sum of the absolute values of the curvatures. As indicated in Table 20 and as discussed below, these design advantages are also reflected in Embodiments 13-18. In Figure 12A, the first relay extends between "surface 8" and surface 14. In Figure 12B, the second relay extends between surfaces 16 and 19, and in Figure 12C, the third relay extends between surfaces 21 and 24. The color correction in Embodiment 12 is performed by the first transfer or relay, and in particular, at surface 11. The optical performance of the system is quite good, with the peak-to- valley wavefront aberration and the maximum axial chromatic aberration being 0.34 and 0.22 waves, respectively. The embodiment of Figures 13A-D is similar to that of Embodiment 12; however, the second relay rather than the first relay is now the color correcting relay, with basically all of the color correction in the system being performed at optical surface 18. Further, the color correction is performed in the second half of the color correcting relay, in contrast with the embodiment of Figures 12A-D, in which the color correction is performed in the first half of the color correcting relay. Thus, the color correction may be placed in any group of elements. In Figure 13A, the first relay extends between "surface 8" and surface 13. In Figure 13B, the second relay extends between surfaces 15 and 19, and in Figure 13C, the third relay extends between surfaces 21 and 24. The optical performance of the system is quite good, with the peak-to-valley wavefront aberration and the maximum axial chromatic aberration being 0.32 and 0.19 waves, respectively. In the embodiment of Figures 14A-D, the color correcting surface (surface 23) has been moved to the third relay, which extends between surfaces 20 and 24 in Figure 14D. (In Figure 14A, the first relay extends between "surface" 8 (i.e., the focal surface at the input focal plane) and surface 13, and in Figure 14B, the second relay extends between surface 15 and surface 18.) Nevertheless, the optical performances of Embodiments 12-14 are substantially comparable, with the peak-to-valley wavefront aberration and the maximum axial chromatic aberration in Embodiment 14 being 0.51 and 0.17 waves, respectively. The embodiment of Figures 15A-D has just 8 optical elements with optical power. This design, like the other embodiments herein that include three relays, approaches the theoretical limit of 7 curved surfaces needed for a three relay endoscope. This limit is based on the fact that each relay has two or more curved surfaces and the objective has at least one curved surface. Although the maximum values of the peak to valley wavefront aberration and the maximum axial chromatic aberration in Embodiment 15 (0.81 and 0.68 waves, respectively) are higher than in the other field expander embodiments of Figures 12-18, the overall performance is still good, and the Petzvalsum is just 0.04/mm. In Figure 15 A, the first relay extends between "surface 8" and surface 13. In Figure 15B, the second relay extends between surfaces 15 and 18, and in Figure 15C, the third relay extends between surfaces 20 and 23. The color correction is basically provided by surface 11. In the embodiment illustrated in Figures 16A-D, the components with curved surfaces are advantageously made of plastic, COC, or polystyrene, which makes the components relatively inexpensive. The rods with flat surfaces can be made of glass or of plastic, or they-sJan be molded as part of the components with the curved surfaces. However, the use of plastic materials can present special problems, e.g., the refractive index of these materials is relatively low. One approach, to combine some of the attractive features of plastic and glass, is used in this embodiment. In particular, plastic elements are cemented onto the flat faces of glass rods, resulting in an endoscope that is inexpensive but has good performance. For example, the peak-to-valley wavefront aberration is 0.41 waves, and the maximum axial chromatic aberration is 0.19 waves. In Figure 16 A, the first relay extends between "surface 8" and surface 17. In Figure 16B, the second relay extends between surfaces 19 and 23, and in Figure 16C, the third relay extends between surfaces 25 and 30. The color correction is basically provided by surface 13. In the embodiment of Figures 17A-D, aspheric surfaces are molded into glass rods, such that the rod and lens form a single piece, thereby reducing the number of optical elements. The peak-to-valley wavefront distortion has been reduced to 0.28 waves, which is less than that of Embodiment 16, and the maximum axial chromatic aberration is only 0.28 waves. The color correction is basically provided by surface 11. The embodiment illustrated in Figures 18A-D is similar to that of Figures 12A-D, except that the longer elements in Figures 12A-D have now been broken up into two shorter segments by introducing a flat-flat interface within each of the longer elements. Although this increases the number of optical pieces in the endoscope, the flexibility of the endoscope is greatly enhanced (so that the chance of the endoscope breaking during use is reduced), without diminishing the optical performance. The first optical relay is shown in Figure 18A to extend between "surface" 8 and surface 20. The second relay (Figure 18B) extends between surface 22 and surface 32, and the third relay extends between surface 34 and surface 43. The color correction is basically provided by surface 14: It is thus evident from the embodiments herein that three groups (an objective, a field lens, and a relay lens) can be integrated to yield an endoscope in such a way that the sum of the absolute values of the powers of the individual optical elements is greatly reduced. The reduction in the optical power reduces the amount of aberrations to be corrected, which considerably reduces the complexity of the optical system, thereby reducing its cost. An additional and often valuable feature of some embodiments is that the entrance pupil is located outside the system, thereby facilitating the addition of other optical components such as prisms. In Tables 1-18, the following abbreviations are used: "CC stands for "Conic constant," and is equal to "k" in Equation 1; "AD" represents the aspheric constant "d" in Equation 1; and "AE" represents the aspheric constant "e" in Equation 1. Equation 1 below is the well-known formula for describing an aspheric surface: in which z is in the direction of the optical axis, p is the distance from the optical axis, and c is the surface curvature (1/RD). The aspheric constants f and g in the exemplary Embodiments 1-18 are equal to zero. The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within that scope. TABLE 1 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.510 7.517 0.000 1 Infinity -0.510 0.260 0.000 2 2.600 1.400 ACRYLIC 4.000 -52.000 3 -1.600 3.000 4.000 -7.500 4 4.000 3.000 ACRYLIC 6.000 -12.000 5 -3.800 33.000 6.000 0.000 6 18.000 2.000 ACRYLIC 6.000 0.000 7 -24.760 51.640 6.000 0.000 8 Infinity 7.473 0.000 EFL -5.517 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 8 > IMAGE PLANE TABLE 2 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 6.928 0.000 1 Infinity 0.600 0.240 0.000 2 Infinity 1.200 ACRYLIC 2.400 0.000 3 -1.100 7.400 2.400 -0.400 4 Infinity 1.500 LAH66 6.000 0.000 5 -6.300 36.800 6.000 0.000 6 Infinity 1.500 ACRYLIC 6.000 0.000 7 -11.810 44.850 6.000 -3.000 8 Infinity 6.852 0.000 EFL -5.544 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 8 = IMAGE PLANE TABLE 3 JRF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 7.000 0.000 1 Infinity 6.000 0.240 0.000 2 Infinity 3.000 ACRYLIC 9.200 0.000 3 -4.700 51.300 9.200 -0.650 4 25.700 7.000 ACRYLIC 21.800 0.000 5 -11.700 18.000 21.800 -2.900 6 7.000 2.000 ACRYLIC 6.000 0.000 7 -13.477 6.717 6.000 -560.000 8 Infinity 7.038 0.000 EFL -3.217 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 8 = IMAGE PLANE TABLE 4 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 6.928 0.000 1 Infinity 2.000 0.240 0.000 2 -5.000 1.800 ACRYLIC 4.400 0.000 3 -2.100 1.700 4.400 -0.560 4 5.830 2.000 PHM52 6.400 0.000 5 Infinity 48.000 SF6 6.400 0.000 6 Infinity 2.000 ACRYLIC 6.400 0.000 7 -7.010 36.500 6.400 -1.300 8 Infinity 6.979 0.000 EFL -4.845 SURF O = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 8 - IMAGE PLANE TABLE 5 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 8.402 0.000 1 Infinity 0.200 0.180 0.000 2 Infinity 3.000 LAK8 3.600 0.000 3 Infinity 1.500 LAH66 3.600 0.000 4 -4.000 0.200 5.000 0.000 5 13.500 1.500 LAH66 5.000 0.000 6 -13.500 9.500 5.000 0.000 7 Infinity 1.500 LAH66 6.000 0.000 8 -10.900 30.800 6.000 0.000 9 Infinity 1.200 LASF32 6.000 0.000 10 8.800 2.000 SK5 6.000 0.000 11 -8.470 42.550 6.000 0.000 12 Infinity 7.112 0.000 EFL -5.492 SURF O = OBJECT PLANE SURF 1 - ENTRANCE PUPIL PLANE SURF 12 = IMAGE PLANE TABLE 6 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity Infinity 0.000 0.000 1 Infinity 3.200 0.312 0.000 2 4.900 2.500 ACRYLIC 6.000 -1.500 3 -2.900 18.600 6.000 -2.500 4 Infinity 2.000 ACRYLIC 6.000 0.000 5 -8.800 24.000 6.000 -0.700 6 -7.000 1.200 POLYCARB 4.000 1.400 7 Infinity 2.000 LAKN7 6.000 0.000 8 -6.550 40.510 6.000 0.000 9 Infinity 8.794 0.000 EFL -7.817 SURF O = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 9 = IMAGE PLANE TABLE 7 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 8.402 0.000 1 Infinity 1.900 0.240 0.000 2 Infinity 2.500 ACRYLIC 5.000 0.000 3 -2.000 2.700 5.000 -0.660 4 Infinity 2.000 ACRYLIC 6.000 0.000 5 -16.800 25.000 6.000 32.000 6 Infinity 2.000 ACRYLIC 7.000 0.000 7 -9.600 31.200 7.000 -1.200 8 Infinity 2.000 ACRYLIC 6.000 0.000 9 -17.850 24.680 6.000 -28.000 10 Infinity 7.917 0.000 EFL -5.302 SURF O = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 10 ■ = IMAGE PLANE TABLE 8 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 6.000 6.928 0.000 1 Infinity 3.200 0.300 0.000 2 Infinity 2.500 ACRYLIC 5.400 0.000 3 -2.500 3.000 5.400 -0.640 4 Infinity 2.000 ACRYLIC 6.400 0.000 5 -26.000 24.700 6.400 57.000 6 Infinity 2.000 ACRYLIC 6.400 0.000 7 -9.200 25.000 6.400 -1.000 8 -4.300 1.200 POLYCARB 4.400 -0.300 9 Infinity 2.000 ACRYLIC 6.000 0.000 10 -3.610 28.350 6.000 -0.700 11 Infinity 6.930 0.000 EFL -5.602 SURF 0 = OBJECT PLANE SURF 1 - ENTRANCE PUPIL PLANE SURF 11 = IMAGE PLANE TABLE 9 LIRF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 3.000 3.464 0.000 1 Infinity 2.400 0.300 0.000 2 12.400 3.000 ACRYLIC 5.400 0.000 3 -2.320 9.700 5.400 -0.800 -7.600 2.000 ACRYLIC 6.400 0.000 -8.100 15.900 6.400 2.800 6 Infinity 2.000 ACRYLIC 6.400 0.000 7 -10.000 28.500 6.400 -1.200 -24.000 1.200 POLYCARB 6.000 70.000 5.000 2.500 ACRYLIC 6.000 0.000 10 -6.360 29.820 6.000 0.000 11 Infinity 7.031 0.000 EFL -4.891 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 11 = IMAGE PLANE TABLE 10 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.000 13.426 0.000 1 Infinity 0.100 0.200 0.000 2 Infinity 3.800 SF6 5.380 0.000 3 Infinity 1.800 LAH66 5.380 0.000 4 -4.300 0.200 6.400 0.000 5 11.400 1.500 LAH66 6.400 0.000 6 -17.000 10.000 6.400 0.000 7 Infinity 2.000 LAH66 6.400 0.000 8 . -18.900 40.300 6.400 0.000 9 13.000 2.000 TIH53 6.400 0.000 10 8.500 2.500 FPL51 6.400 0.000 11 -19.300 39.800 6.400 0.000 12 Infinity 2.000 LAH66 6.400 0.000 13 -8.340 20.000 6.400 0.000 14 Infinity 2.000 SP15 6.400 0.000 15 -8.830 14.040 6.400 0.000 16 Infinity 6.607 0.000 EFL 3.782 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE; SURF 16 = IMAGE PLANE For SURF 15, AD = 9.0E-4, and AE = 2.0E-5. TABLE 11 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 12.000 13.856 0.000 1 Infinity 0.100 0.200 0.000 2 Infinity 4.500 SF6 5.380 0.000 3 Infinity 2.000 LAH66 6.400 0.000 4 -4.300 0.200 6.400 0.000 5 38.000 1.500 LAH66 6.400 0.000 6 -14.000 15.000 6.400 0.000 77 IInnffiinniittyy 1.600 LAH66 6.400 0.000 88 --1144..000000 27.000 6.400 0.000 99 5500..000000 1.200 T1H53 6.400 0.000 1100 44..550000 3.000 FPL51 6.400 0.000 1111 --44..770000 28.800 6.400 0.000 1122 IInnffiinniittyy 2.000 LAH66 6.400 0.000 1133 --1111..000000 26.700 6.400 0.000 1144 IInnffiinniittyy 2.000 LAH66 6.400 0.000 1155 --99..990000 27.300 6.400 0.000 1166 --1144..770000 2.000 LAH66 6.400 0.000 1177 --88..000000 40.700 6.400 0.000 1188 IInnffiinniittyy 2.000 LAH66 6.400 0.000 1199 --2200..333300 50.400 6.400 0.000 2200 IInnffiinniittyy 6.215 0.000 EFL -5.739 SURF 0 = OBJECT PLANE SURF 1 = ENTRANCE PUPIL PLANE SURF 20 = IMAGE PLANE TABLE 12 JRF RD (mm) TH (mm) MEDIUM Di; METER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 SAPPHIRE 1.620 0.000 2 0.700 0.800 1.056 0.000 3 IInnffiinniittyy 11..990000 TIH6 0.880 0.000 4 IInnffiinniittyy 00..660000 TIH6 0.552 0.000 5 IInnffiinniittyy 00..880000 LAH53 0.808 0.000 6 --11..660000 22..770000 1.106 0.000 7 IInnffiinniittyy 33..000000 LAH53 1.628 0.000 8 IInnffiinniittyy 22..885500 LAH53 1.938 0.000 9 --44..330000 00..330000 2.497 0.000 10 IInnffiinniittyy 3300..660000 TIH6 2.490 0.000 11 33..660000 11..220000 PHM52 2.418 0.000 12 -7.160 0.300 2.504 0.000 13 10.100 23.750 LAH53 2.486 0.000 14 Infinity 2.000 2.094 0.000 15 Infinity 2.000 2.033 0.000 16 7.160 28.200 LAH53 2.493 0.000 17 Infinity 0.400 2.469 0.000 18 7.540 28.700 LAH53 2.490 0.000 19 -16.000 2.000 2.448 0.000 20 Infinity 2.000 2.230 0.000 21 10.100 30.000 LAH53 2.491 0.000 TABLE 12 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 -7.540 0.400 2.425 0.000 23 Infinity 28.200 LAH53 2.427 0.000 24 Infinity 1.955 2.489 0.000 25 Infinity 2.497 0.000 EFL -1. 445555 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 25 = IMAGE PLANE TABLE 13 URF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 SAPPHIRE 1.620 0.000 2 0.700 0.800 1.056 0.000 3 Infinity 1.900 TIH6 0.880 0.000 4 Infinity 0.600 TIH6 0.552 0.000 5 Infinity 0.800 LAH53 0.808 0.000 6 -1.470 2.200 1.103 0.000 7 Infinity 3.000 LAH53 1.408 0.000 8 Infinity 2.850 LAH53 1.628 0.000 9 -4.000 0.300 2.342 0.000 10 Infinity 29.500 TIH6 2.341 0.000 11 Infinity 0.300 2.493 0.000 12 7.570 27.000 LAH53 2.518 0.000 13 Infinity 2.000 2.189 0.000 14 Infinity 2.000 2.155 0.000 15 7.570 32.700 LAH53 2.505 0.000 16 -7.570 0.400 2.415 0.000 17 10.060 1.500 PHM52 2.383 0.000 18 -2.760 27.000 TIH6 2.262 0.000 19 -7.000 2.000 2.567 0.000 0 Infinity 2.000 2.028 0.000 1 Infinity 24.000 LAH53 2.080 0.000 TABLE 13 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 -7.000 0.400 2.508 0.000 23 Infinity 29.500 LAH53 2.506 0.000 24 Infinity 1.850 2.442 0.000 25 Infinity 2.443 0.000 EFL -1.447 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 25 = IMAGE PLANE TABLE 14 >URF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 SAPPHIRE 1.619 0.000 2 0.700 0.800 1.055 0.000 3 Infinity 1.900 LAH53 0.880 0.000 4 Infinity 0.600 LAH53 0.552 0.000 5 Infinity 1.300 LAH53 0.808 0.000 6 -1.730 3.000 1.307 0.000 7 Infinity 3.000 LAH53 1.707 0.000 8 Infinity 3.300 LAH53 1.920 0.000 9 -4.800 0.300 2.480 0.000 10 Infinity 31.500 T1H6 2.477 0.000 11 Infinity 0.300 2.397 0.000 12 7.500 25.700 LAH53 2.415 0.000 13 Infinity 2.000 2.174 0.000 14 Infinity 2.000 2.154 0.000 15 6.900 31.500 LAH53 2.499 0.000 16 -6.900 0.400 2.511 0.000 17 Infinity 21.900 LAH53 2.489 0.000 18 Infinity 2.000 TIH6 2.128 0.000 19 Infinity 2.000 2.087 0.000 20 7.500 31.500 LAH53 2.500 0.000 21 -6.100 0.400 2.475 0.000 TABLE 14 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 21.400 1.500 BAFN11 2.318 0.000 23 -2.270 25.700 TIH6 2.192 0.000 24 Infinity 2.100 2.471 0.000 25 Infinity 2.512 0.000 EFL -1.443 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 25 • - IMAGE PLANE TABLE J 5 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 LAH66 1.486 . 0.000 ' 2 0.600 0.800 0.937 0.000 3 Infinity 1.800 LAH66 0.819 0.000 4 Infinity 0.700 LAH66 0.611 0.000 5 Infinity 1.000 LAH66 0.908 0.000 6 -1.600 2.900 1.277 0.000 7 Infinity 3.000 LAH66 1.577 0.000 8 Infinity 4.000 LAH66 1.745 0.000 9 -4.600 0.300 2.405 0.000 10 Infinity 31.000 TIH6 2.405 0.000 11 4.500 0.010 2.449 5.300 12 2.700 28.000 LAH66 2.550 0.000 13 Infinity 2.000 1.927 0.000 14 Infinity 2.100 1.864 0.000 15 7.600 28.000 LAH66 2.159 -2.700 16 Infinity 0.300 2.438 0.000 17 7.100 20.500 LAH66 2.445 11.300 18 Infinity 2.000 1.832 0.000 19 Infinity 2.000 1.872 0.000 20 5.620 31.000 LAH66 2.463 -1.000 21 -6.800 0.300 2.420 - -10.700 TABLE 15 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 Infinity 31.000 LAH66 2.420 0.000 23 Infinity 1.970 2.514 0.000 24 Infinity 2.688 0.000 EFL -1.563 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 24 = IMAGE PLANE TABLE 16 URF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.400 CDC 1.810 0.000 2 0.530 0.400 0.944 0.000 3 Infinity 2.000 SF6 0.899 0.000 4 Infinity 1.000 SF6 0.459 0.000 5 Infinity 1.300 COC 0.948 0.000 6 -1.200 2.400 1.541 0.000 7 Infinity 4.200 SF6 1.717 0.000 8 Infinity 2.800 SF6 1.870 0.000 9 Infinity 0.300 2.320 0.000 10 3.700 1.500 COC 2.503 -0.300 11 Infinity 29.200 LAH66 2.473 0.000 12 Infinity 1.500 POLYSTYR 2.175 0.000 13 3.120 1.500 COC 2.287 0.000 14 -4.310 0.500 2.487 -3.450 15 Infinity 29.200 LAH66 2.487 0.000 16 Infinity 1.500 COC 2.503 0.000 17 -5.120 2.300 2.504 -4.300 18 Infinity 2.200 2.167 0.000 19 Infinity 25.000 SF6 2.120 0.000 20 Infinity 0.300 2.458 0.000 21 4.470 1.500 COC 2.495 1.080 TABLE 16 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 Infinity 19.600 LAH66 2.322 0.000 23 Infinity 2.300 1.756 0.000 24 Infinity 2.200 1.775 0.000 25 3.420 1.500 COC 2.482 -7.200 26 Infinity 25.000 SF6 2.482 0.000 27 Infinity 1.500 COC 2.488 0.000 28 -5.120 0.300 2.489 -1.800 29 Infinity 25.000 SF6 2.465 0.000 30 Infinity 5.520 2.495 0.000 31 Infinity 2.620 0.000 EFL -1.626 SURF 0 - OBJECT PLANE SURF 4 = PUPIL PLANE SURF 31 = IMAGE PLANE TABLE 17 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 TIH6 1.513 0.000 2 0.650 0.800 0.979 0.000 3 Infinity 1.800 TIH6 0.836 0.000 4 Infinity 0.700 TIH6 0.591 0.000 5 Infinity 1.500 LAH51 0.887 0.000 6 -1.680 2.800 1.457 0.000 7 Infinity 3.000 LAH51 1.546 0.000 8 Infinity 5.000 LAH51 1.597 0.000 9 -4.600 0.300 2.493 0.580 10 Infinity 25.700 TIH6 2.464 0.000 11 3.470 1.200 PHM52 2.286 0.000 12 -3.860 0.300 2.490 0.700 13 Infinity 21.600 LAH51 2.478 0.000 14 Infinity 2.000 2.205 0.000 15 Infinity 2.100 2.159 0.000 16 7.400 33.800 LAH51 2.494 -6.600 17 Infinity 0.400 2.470 0.000 18 6.920 27.900 LAH51 2.497 •9.200 19 Infinity 2.100 2.181 0.000 20 Infinity 2.000 2.141 0.000 21 7.400 29.400 LAH51 2.494 -6.600 TABLE 17 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 -7.700 0.400 2.492 5.600 23 Infinity 27.900 LAH51 2.348 0.000 24 Infinity 1.980 2.496 0.000 25 Infinity 2.634 0.000 EFL -1.509 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 25 = IMAGE PLANE TABLE 18 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 0 Infinity 8.600 26.000 0.000 1 Infinity 0.300 SAPPHIRE 1.593 0.000 2 0:680 0.800 1.032 0.000 3 Infinity 1.863 TIH6 0.864 0.000 4 Infinity 0.672 TIH6 0.559 0.000 5 Infinity 0.728 LAH53 0.845 0.000 6 -1.508 2.170 1.110 0.000 7 Infinity 3.000 LAH53 1.439 0.000 8 Infinity 3.750 LAH53 1.680 0.000 9 -4.230 0.311 2.492 0.000 10 Infinity 13.700 TIH6 2.484 0.000 11 Infinity 0.500 2.428 0.000 12 Infinity 13.700 TIH6 2.425 0.000 13 Infinity 1.000 TIH6 2.385 0.000 14 3.483 1.200 PHM52 2.395 0.000 15 -6.510 0.308 2.493 0.000 16 11.050 1.600 LAH53 2.490 0.000 17 Infinity 7.670 LAH53 2.463 0.000 18 Infinity 0.500 2.328 0.000 19 Infinity 13.300 LAH53 2.312 0.000 20 Infinity 2.000 2.078 0.000 21 Infinity 2.085 2.014 0.000 TABLE 18 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC 22 6.830 1.800 LAH53 2.490 0.000 23 Infinity 13.300 LAH53 2.472 0.000 24 Infinity 0.500 2.333 0.000 25 Infinity 13.300 LAH53 2.324 0.000 26 Infinity 0.400 2.353 0.000 27 7.850 1.400 LAH53 2.487 0.000 28 Infinity 13.300 LAH53 2.488 0.000 29 Infinity 0.500 2.491 0.000 30 Infinity 13.300 LAH53 2.492 0.000 31 Infinity 1.200 LAH53 2.495 0.000 32 -14.020 2.044 2.496 0.000 33 Infinity 2.044 2.187 0.000 34 14.020 1.200 LAH53 2.429 0.000 35 Infinity 13.300 LAH53 2.427 0.000 36 Infinity 0.500 2.395 0.000 37 Infinity 13.300 LAH53 2.393 0.000 38 Infinity 1.400 LAH53 2.433 0.000 39 -7.850 0.400 2.473 0.000 40 Infinity 13.300 LAH53 2.373 0.000 41 Infinity 0.500 2.427 0.000 42 Infinity 13.300 LAH53 2.431 0.000 43 Infinity 3.573 2.493 0.000 44 Infinity 2.524 0.000 TABLE 18 SURF RD (mm) TH (mm) MEDIUM DIAMETER (mm) CC EFL -1.475 SURF 0 = OBJECT PLANE SURF 4 = PUPIL PLANE SURF 44 = IMAGE PLANE TABLE 19 MEDIUM <* • »480ιm • "546-m • »644ιm MANUFACTURER Acrylic 57.4 1.498 1.494 1.489 BAF 11 48.4 1.677 1.670 1.633 Schott COC 55.7 1.541 1.536 1.531 FPL 51 81.6 1.495 1.498 1.502 Ohara LAH51 44.2 1.799 1.790 1.781 Ohara LAH 53 40.9 1.821 1.811 1.801 Ohara LAH 66 49.6 1.784 1.776 1.769 Ohara LAK 8 .53.8 1.723 1.716 1.710 Schott LAK 7 58.5 1.660 1.654 1.649 Schott LASF 32 30.4 1.824 1.810 1.797 Schott SAPPHIRE 72.2 1.776 1.771 1.765 SF6 25.4 1.830 1.813 1.798 Schott SF15 30.1 1.693 1.704 1.717 Schott SK5 61.3 1.596 1.591 1.587 Schott TIH6 25.4 1.830 1.813 1.798 Ohara PHM52 63.4 1.625 1.620 1.616 Ohara Polycarbonate 29.9 1.601 1.590 1.581 Polystyrene 30.9 1.605 1.595 1.586 TABLE 20 2 3 4 5 6 7 8 9 10 11 12 13 1 15 16 17 18 19 20 21 22 23 24 25 26 IMA FOV Mag SC Rl Oe Le Le Le Le Le Ing c. c.s. as as as as dis ptz wv ax NP CA s/r deg no tot tot obj rel rel rsl m to tot obj rel rel rel +,- +,- +,- +,- +,- <-c <, <, <, .020 60 1.0 1.62 1 3 3,0 1,0 2,0 10 6 6,0 2,0 4,0 -2 -.5 .7 .90 -.5 5.0 1.62 .020 60 1.0 1.15 1 3 3,0 1,0 2,0 10 3 3,0 1,0 2,0 -2 -.4 .3 .80 0.6 5.3 1.15 .020 60 1.0 0.55 1 3 3,0 1,0 2,0 10 5 5,0 1,0 4,0 -1 -.1 .1 .21 6.0 20 0.55 .020 60 1.0 0.99 1 4 3,0 2,0 1,0 10 4 3,1 2,1 1,0 2 -.2 .2 .31 2.0 5.1 0.99 .015 70 1.0 0.84 1 5 4,1 2,0 2,1 10 7 6,1 3,0 3,1 -16 -.2 .3 .12 1.9 5.2 0.84 .020 60 0.0 0.96 1 4 3,1 1,0 2,1 94 5 4,1 2,0 2,1 -3 -.2 .4 .14 3.2 5.2 0.96 .020 70 1.0 0.72 1 4 4,0 2,0 2,0 10 4 4,0 2,0 2,0 -6 -.2 .2 .63 1.9 5.2 0.72 .025 60 1.0 1.06 1 5 4,1 2,0 2,1 10 5 4,1 2,0 2,1 -1 -.1 .2 .31 3.2 5.2 1.06 .025 60 2.0 1.47 1 5 3,2 1,0 2,2 10 9 6,3 2,0 4,3 1 -.2 .1 .03 2.4 5.8 1.47 .025 80 -0.5 1.03 2 7 6,1 2,0 2,1 2,0 15 1 9,1 3,0 4,1 2,0 -2 -.3 .3 .35 2.2 5.5 0.52 .017 60 0.5 1.51 3 9 8,1 2,0 2,1 2,0 2,0 25 1 11, 3,0 4,1 2,0 2,1 -11 -.3 .4 .04 2.6 5.5 0.50 .061 110 .15 3.65 3 10 7,2 1,1 3,1 2,0 1,0 19 1 10, 1,1 4,1 3,0 2,0 -39 -.1 .3 .22 -.8 2.5 1.22 .061 110 .15 3.86 3 10 6,2 1,1 2,0 2,1 1,0 19 1 9,2 1,1 2,0 5,1 1,0 -40 -.1 .3 .19 -.8 2.5 1.29 .061 110 .15 3.86 3 10 6,2 1,1 2,0 1,0 2,1 19 1 9,2 1,1 2,0 2,0 4,1 -39 -.0 .5 .17 -.8 2.5 1.29 .057 110 .17 3.70 3 9 6,2 1,1 2,1 2,0 1,0 19 9 7,2 1,1 2,1 2,0 2,0 -40 .04 .8 .68 -.7 2.5 1.23 .055 110 .17 4.77 3 16 7,2 1,1 3,1 1,0 2,0 19 1 8,2 1,1 4,1 1,0 2,0 -42 -.1 .4 .19 -.9 2.5 1.59 TABLE 20 2 3 4 5 6 7 8 9 10 11 12 13 1 15 16 17 18 19 20 21 22 23 24 25 2 NA FOV Mag SC Rl Oe Le Le Le Le Le Ing c. as. as c.s c.s as dis ptz wv ax NP CA s .059 110 .16 3.73 3 10 6,2 1,1 2,1 2,0 1,0 19 1 8,2 1,1 3,1 2,0 2,0 -40 .01 .2 .28 -J 2.5 1 .060 110 .16 3.73 3 23 9,2 1,1 3,1 3,0 2,0 19 1 10, 1,1 4,1 3,0 2,0 -38 -.0 .2 .26 -.8 2.5 1 Column 1 Number of example. Column 2 Numerical aperture at image. (The sine of the marginal axial ray angle times the refractive index.) Column 3 Total field of view in degrees. Column 4 Magnification. Column 5 Sum of the absolute values of all curvatures, in 1 /mm. Column 6 Number of relays. Column 7 Total number of optical elements, plano-plano rods included, prism excluded. Column 8 Total number of positive and of negative lens elements. Column 9 Number of positive and of negative lens elements in the objective part. Column 10 Number of positive and of negative lens elements in the first relay. Column 11 Number of positive and of negative lens elements in the second relay. Column 12 Number of positive and of negative lens elements in the third relay. Column 13 Distance of the first surface or the object plane to the image plane in mm. Column 14 Total number of curved surfaces. Column 15 Number of curved convex surfaces and of concave surfaces. Column 16 Number of convex and of concave surfaces of the objective part. Column 17 Number of convex and of concave surfaces of the first relay. Column 18 Number of convex and of concave surfaces of the second relay. Column 19 Number of convex and of concave surfaces of the third relay. Column 20 Maximum image distortion in %. Column 21 Petzval curvature in 1 /mm. Column 22 Peak to valley wavefront aberration over the full field at e-light in waves. Column 23 Maximum axial wavefront aberration between F- and C-light in waves. Column 24 Entrance pupil location in mm towards first surface of first lens (air equivalent value) Column 25 Maximum clear aperture of endoscope in mm. Column 26 Sum of the absolute values of the curvatures divided by the number of relays, in 1/mm.

Claims: WHAT IS CLAIMED IS: 1. A color corrected optical endoscope system including a plurality of elements, comprising: an objective element; and a relay system providing substantially all color correction for said endoscope system using at least one curved optical interface providing color correction, said objective element and said relay system optically aligned to transfer an image from an input plane of said objective element to an output plane of said endoscope system, each of said plurality of optical elements being uniformly refractive and suitable for use with at least one of the e, FN, and CN spectral lines. 2. A color corrected optical endoscope system including an optical system having a plurality of optical elements, comprising: an objective element; and a first relay system having a first number of curved surfaces, said first relay system including an optical interface having a curvature that provides substantially all of the color correction for said endoscope system, said objective element and said first relay system optically aligned to transfer an image from an input plane of said objective element to an output plane of said endoscope system, wherein said plurality of optical elements are suitable for use with at least a portion of the spectrum extending from the F to the C spectral line. 3. A color corrected optical endoscope including a plurality of optical elements, comprising: an objective; and a relay system, said relay system having at least one optical interface providing color correction for said endoscope, said objective providing substantially no color correction, said objective and said relay system aligned along a common optical axis, and said plurality of optical elements being suitable for use with at least a portion of the spectrum extending from the F to the C spectral line. 4. A color corrected endoscopic imaging system including a plurality of optical elements, comprising: an objective for imaging an object onto a focal plane; and at least one relay that is optically aligned with said objective along a common optical axis, said relay including curved surfaces, at least one curved interface providing color correction for said endoscopic imaging system, wherein the number of said curved surfaces in said relay is not greater than 5. 5. A color corrected imaging system for use with an endoscope and including a plurality of optical elements, comprising: an objective having an optical axis; and at least one relay aligned with said objective along the optical axis, said objective having not more than 3 curved surfaces, at least one of said optical elements providing color correction for said imaging system. 6. A color corrected endoscope including a plurality of optical elements, said endoscope comprising: an objective system; and at least three relay systems optically aligned with said objective system, wherein said objective system and three of said at least three relay systems together include not more than 13 curved surfaces. 7. A color corrected endoscope including a plurality of optical elements, said endoscope comprising: an objective system; and at least two relay systems including optical elements, said at least two relay systems optically aligned with said objective system, wherein said objective system and two of said at least two relay systems together include not more than 10 curved surfaces, said optical elements suitable for use with at least a portion of the spectrum extending from the F to the C spectral line, and at least one of said optical elements providing color correction to said endoscope. 8. A color corrected endoscope, including a plurality of lens elements, comprising: an objective; and at least one relay, wherein one of said at least one relay includes not more than 3 lens elements, said objective and said at least one relay aligned to transfer an image from an input plane of said objective to an output plane of said endoscope, at least one of said lens elements providing color correction to said endoscope. 9. A color corrected endoscopic system including a plurality of optical elements, comprising: an objective group; and at least two relay groups aligned with said objective group along an optical axis, one of said relay groups including no optical elements of negative optical power, and another of said relay groups providing color correction to said endoscopic system. 10. A color corrected endoscopic system including a plurality of optical elements, comprising: an objective; and at least one relay group aligned with said objective along an optical axis, said objective and said at least one relay group together including not more than 2 elements of negative optical power, at least one of said plurality of optical elements providing color correction for said endoscopic system. 11. A color corrected optical endoscope including a plurality of optical elements, comprising: means for forming a first image of an object; and means for relaying the first image and forming a second image, wherein said relaying means includes means for correcting chromatic aberrations, whereas said means for forming a first image includes substantially no means for correcting chromatic aberrations, said means for forming a first image and said relaying means being aligned along a common optical axis, said plurality of optical elements being suitable for use with at least a portion of the spectrum extending from the F to the C spectral line. 12. An optical system including a plurality of optical elements, comprising: an objective; a color-correcting relay providing substantially all color correction for said system using at least one curved interface providing color correction; and a non-color correcting relay, wherein said non-color correcting relay, said objective, and said color- correcting relay are aligned along a common optical axis and optically aligned to transfer an image from an input plane of said objective to an output plane of said optical system, in which each of said plurality of optical elements is uniformly refractive and suitable for use with at least a portion of the spectrum extending from the F to the C spectral line. 13. A method of imaging an object, comprising: forming a first image of the object with a non-color correcting objective system; providing at least a first and a second relay system; aligning the objective system and the first and second relay systems along a common optical axis; receiving the first image from the objective system with the first relay system to form a second image; transferring the second image from the first relay system using the second relay system to form a third image of the object; and correcting chromatic aberrations with one of the relay systems by using at least one optical interface, wherein the objective system and the plurality of relay systems are suitable for use with at least a portion of the spectrum extending from the F to the C spectral line. 14. A method of imaging an object, comprising: providing an objective for forming a first image of the object; providing at least three relay systems optically aligned with the objective system, wherein the objective and the relay systems together include not more than 13 curved surfaces, the objective and the relay systems being suitable for use with at least a portion of the spectrum extending from the F to the C spectral line; receiving the first image with one of the relay systems; forming an output image with another of the relay systems, in which the output image can be received by a viewer; and providing color correction to the output image with at least one curved interface. 15. A method of designing an integrated aberration corrected endoscope, comprising: providing a plurality of optical groups, wherein the groups are aligned along a common optical axis and each of the groups produces a respective image at a respective focal plane, the groups including an objective and at least one relay; and providing a first one of the groups with more aberration correction than the first group requires to be aberration corrected; and providing a second one of the groups with less aberration correction than the second group requires to be aberration corrected, wherein the aberration correction of the first group compensates for lack of aberration correction in the second group to produce an aberration corrected endoscope. 16. An integrated aberration corrected endoscope, comprising: a first optical group, said first group having more aberration correction than said first group requires to be aberration corrected; and at least a second optical group, said second group having less aberration correction than said second group requires to be aberration corrected, in which the aberration correction of said first group compensates for lack of aberration correction in said second group to produce said integrated aberration corrected endoscope, wherein said groups are aligned along a common optical axis and each of said groups produces a respective image at a respective focal plane, said groups including an objective and at least one relay. 17. An optical system for transferring an image from a first plane to a second plane via an intermediate plane, comprising: an objective comprising at least one optical element disposed between the first plane and the intermediate plane for forming a relatively uncorrected image at the intermediate plane; and a relay comprising at least one optical element disposed between the intermediate plane and the second plane for forming a relatively more corrected image at the second plane.

Inventors: HOOGLAND JAN, HOOGLAND, JAN
Applicants: HOOGLAND JAN, HOOGLAND, JAN
Application year: 2001
Main classification: G02B21
IPC codes: A61B1, G02B13, G02B23