Apparatus for recording an image by irradating a plurality of light beams on a recording surface

An aperture plate is disposed between a reduction optical system (imaging optical system) and a light source unit in which a plurality of light source parts each emitting a light beam are arranged in a predetermined arrangement pattern. In the aperture plate, a plurality of apertures are arranged in the same pattern as the arrangement pattern of the light source parts. Light beams from the light source parts are directed toward the reduction optical system through the apertures which face the respective light source parts so that reduction images of the apertures are formed on a photosensitive material. Even if the light source parts are located a little displaced from a predetermined arrangement pattern, images of the apertures will be focused on a photosensitive material. This enables easy adjustment of the locations of the light source parts and recording of a high quality image.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a multibeam recording apparatus for 
irradiating a plurality of light beams onto a recording surface. 
2. Description of the Background Art 
FIG. 17 is a view of a conventional multibeam recording apparatus. The 
multibeam recording apparatus is comprised of a light source unit 90 in 
which a plurality of light source parts 91 are arranged in a predetermined 
arrangement pattern, and a reduction optical system (imaging optical 
system) 92 for reducing a plurality of light beams from the light source 
unit 90 and irradiating the reduced light beams onto a photosensitive 
material (recording surface) PM. 
Each light source part 91 comprises a semiconductor laser 93 and a 
collimating lens 94 which are fixed to the main body of the light source 
part (not shown). A light beam from the semiconductor laser 93 is 
collimated into a parallel light beam by the collimating lens 94 to be 
thereafter emitted from a tip portion of the main body of the light source 
part (which is generally indicated at 95 in FIG. 1) toward the reduction 
optical system 92. Here, the tip portion 95 of the main body of the light 
source part functions as an aperture which cuts an unwanted portion of the 
parallel light beam. 
The reduction optical system 92 is comprised of a plurality of optical 
elements. For example, as shown in FIG. 1, receiving parallel light beams 
which travel parallel to an optical axis Z from the light source parts 91 
and which have at predetermined pitches P, the reduction optical system 92 
reduces the light beams at an appropriate magnification M and irradiates 
parallel light beams which have beam pitches BP (=P.multidot.M) and which 
advance parallel to the optical axis Z onto the photosensitive material 
PM. 
Hence, by moving the photosensitive material PM in a primary scanning 
direction X (which is perpendicular to the plane of FIG. 17) while step 
feeding the light source unit 90 and the reduction optical system 92 in a 
sub scanning direction Y, a two-dimensional image is recorded on the 
photosensitive material PM. 
If high quality recording of a predetermined image using the multibeam 
recording apparatus having such a construction above is desired, the light 
beams from the respective light source parts 91 must travel parallel to 
the optical axis Z of the reduction optical system 92 and the light source 
parts 91 must be arranged with equal distances from each other (i.e., 
constant pitches P). If these requirements are not satisfied, light beam 
spots will not be formed equidistant from each other on the photosensitive 
material PM, resulting in a varied quality image recorded on the 
photosensitive material PM. 
For this reason, in the conventional multibeam recording apparatus, the 
direction of the light beams from the respective light source parts 91 
must be adjusted and the light source parts 91 must be arranged with a 
high accuracy in a predetermined arrangement pattern (with constant 
pitches P in the example described above), which requires a long time. 
SUMMARY OF THE INVENTION 
The present invention is directed to a multibeam recording apparatus for 
irradiating a plurality of light beams onto a recording surface to 
recording an image. The multibeam recording apparatus comprises: a light 
source unit including a plurality of light source parts which are arranged 
in a first arrangement pattern, each of the light source parts emitting a 
single light beam; an imaging optical system having an optical axis, the 
imaging optical system dispose between the light source unit and the 
recording surface; and an aperture plate having a plurality of apertures 
which are arranged in a second arrangement pattern identical or similar to 
the first arrangement pattern, the aperture plate being disposed between 
the light source unit and the imaging optical system so that each of the 
apertures is faced the corresponding light source part. 
According to a preferred embodiment of the present invention, the light 
source parts are disposed on a flat surface substantially perpendicular to 
the optical axis, the aperture plate is formed in the configuration of the 
flat surface and the first and second arrangement patterns are identical 
to each other. 
According to another preferred embodiment of the present invention, the 
light source parts are disposed on the spherical surface and the aperture 
plate is formed in the configuration of the spherical surface, and wherein 
the second arrangement pattern is similar to the first arrangement 
pattern. 
Accordingly, it is an object of the present invention to offer a multibeam 
recording apparatus which records a high quality image with simple 
adjustment. 
These and other objects, features, aspects and advantages of the present 
invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A. First Preferred Embodiment 
FIG. 1 is a perspective view of a multibeam recording apparatus according 
to a first preferred embodiment of the present invention. In the multibeam 
recording apparatus, a light source unit 5 for emitting a plurality of 
light beams, an aperture plate 10 and a reduction optical system (imaging 
optical system) 40 which is formed by two lenses 41 and 42 are fixed on a 
base 50 which is movable in a sub scanning direction Y. The base 50 is 
mechanically connected with a driving unit (not shown). This allows that 
when driven by the driving unit, the base 50 moves in the subscanning 
direction Y so that the light source unit 5, the aperture plate 10 formed 
in the configuration of the flat surface and the reduction optical system 
(imaging optical system) 40 move as one unit in the sub scanning direction 
Y. The multibeam recording apparatus also comprises a rotation cylinder 80 
which is disposed for free rotation in a primary scanning direction X. 
Hence, recording of a two-dimensional image on a photosensitive material 
PM is attained by rotating the rotation cylinder 80 in the primary 
scanning direction X with the photosensitive material PM wound around the 
same and a plurality of light beams from the light source unit 5 
irradiated upon the same through the aperture plate 10 and the reduction 
optical system 40 while step feeding the base 50 in the sub scanning 
direction Y. 
FIG. 2 is a view showing an optical system of the multibeam recording 
apparatus of FIG. 1. In FIG. 2, the light source unit 5 comprises a 
plurality of light source parts 1. Each light source part 1 is comprised 
of a semiconductor laser 2 and a collimating lens 3 for collimating a 
light beam from the semiconductor laser 2. Between the light source unit 5 
and the reduction optical system 40, the aperture plate 10 in which a 
plurality of apertures 9 are bored is located. 
FIGS. 3A and 3B are front views of the light source unit 5 and the aperture 
plate 10. FIG. 3A shows a relation of arrangement (arrangement pattern) of 
the light source parts 1 within the light source unit 5 while FIG. 3B 
shows a relation of arrangement (arrangement pattern) of the apertures 9 
in the aperture plate 10. In the light source unit 5, the plurality of the 
light source parts 1 are arranged at constant pitches Pa in the sub 
scanning direction Y to define one column CL. The columns CL of the light 
source parts 1 are located next to each other in the primary scanning 
direction X in such a manner that ends of adjacent columns CL are 
positioned a distance of Ps/M. The apertures 9 are arranged in an 
identical pattern to the light source parts 1 so that each light source 
part 1 of the light source unit 5 and each aperture 9 of the aperture 
plate 10 correspond to each other. The aperture plate 10 is formed by 
opening the apertures 9 with regular spacings from each other in one black 
metal plate, which is done easily and accurately by a state-of-the-art 
technique. 
The aperture plate 10 having such a structure is disposed at a front focal 
plane FP.sub.41 of the lens 41 in such a manner that the apertures 9 face 
the light source parts 1 of the light source unit 5 (FIG. 2). 
In the reduction optical system 40, the lenses 41 and 42 are located so 
that a rear focal plane of the lens 41 (which has a focal length f.sub.41) 
coincides with a front focal plane of the lens 42 (which has a focal 
length f.sub.42). Thus, the reduction optical system 40 is a so-called 
afocal optical system. The photosensitive material (i.e., recording 
surface) PM is located at a rear focal plane RP.sub.42 of the lens 42. 
Hence, in the first preferred embodiment, the aperture plate 10 and the 
photosensitive material PM are in optical conjugation. The images of the 
apertures 9 of the aperture plate 10 are reduced at the magnification M 
(=f.sub.42 /f.sub.41) of the reduction optical system 40 and imaged on the 
material PM. 
As described above, in the multibeam recording apparatus according to the 
first preferred embodiment, since the apertures 9 are arranged in the 
aperture plate 10 in the same manner in which the light source parts 1 are 
arranged and such aperture plate 10 is located between the light source 
unit 5 and the reduction optical system 40, the light source parts 1 are 
adjusted easily in the light source unit 5. More particularly, this is 
because only if the light beams from the light source parts 1 are parallel 
to the optical axis Z and at least a portion of each light beam is 
irradiated upon the corresponding aperture 9, the image of each apertures 
9 will be formed at predetermined location. That is, as far as the 
conditions above are satisfied, even if the light source parts 1 are a 
little displaced in the direction of the optical axis Z or in the 
directions X and Y which are perpendicular to the optical axis Z, light 
beam spots (i.e., the images of the apertures 9) having a similar pattern 
to the arrangement of the apertures 9 will be always formed on the 
photosensitive material PM. Hence, the quality of a resulting image will 
not be degraded even if adjustment of the light source parts 1 is not very 
accurate. 
In the first preferred embodiment, as shown in FIG. 2, the aperture plate 
10 and the photosensitive material PM are brought into optical conjugation 
with each other by coinciding the aperture plate 10 with the front focal 
plane FP.sub.41 of the lens 41 and coinciding the photosensitive material 
(i.e., recording surface) PM with the rear focal plane RP.sub.42 of the 
lens 42. However, optical conjugation of the aperture plate 10 and the 
photosensitive material PM can be also attained by arranging the aperture 
plate 10, the reduction optical system 40 and the photosensitive material 
PM otherwise. For example, as shown in FIG. 4, when the aperture plate 10 
is located with a displacement in a direction parallel to the optical axis 
Z by a distance .DELTA.S from its location in the arrangement shown in 
FIG. 2, by moving the photosensitive material PM along the optical axis Z 
as a distance .DELTA.T which is obtained by the distance .DELTA.S times a 
square of the magnification M (=f.sub.42 /f.sub.41) of the reduction 
optical system 40 (i.e., .DELTA.T=(f.sub.42 f.sub.41).sup.2 
.multidot..DELTA.S), optical conjugation of the aperture plate 10 and the 
photosensitive material PM is achieved. 
The equation above (.DELTA.T=(f.sub.42 /f.sub.42).sup.2 .multidot..DELTA.S) 
also indicates that the apparatus according to the first preferred 
embodiment is relatively easily completed. This is because due to a fact 
that the magnification M (=f.sub.42 /f.sub.41) of the reduction optical 
system (imaging optical system) 40 of the multibeam recording apparatus is 
around 1/100 to 1/1000 in general, even if the aperture plate 10 is 
displaced in the direction parallel to the optical axis Z by the distance 
.DELTA.S, the location of the photosensitive material PM so as to be in 
optical conjugation with the aperture plate 10 will be displaced only by 
1/10.sup.4 to 1/10.sup.6 of .DELTA.S in the direction of the optical axis 
Z. Such a little displacement is equal to almost no influence on the 
quality of an image, and therefore, positioning of the aperture plate 10 
needs not be very accurate. 
FIG. 5 is a view showing the multibeam recording apparatus of the first 
preferred embodiment with an improved structure. In this improved 
structure, the light source unit 5 is formed by two light source arrays 5A 
and 5B which are arranged in the direction parallel to the optical axis Z. 
Each one of the light source arrays 5A and 5B includes a plurality of 
light source parts 1 which are arranged in a predetermined arrangement 
pattern. While light beams from the light source array 5A are irradiated 
directly upon the aperture plate 10, light beams from the light source 
array 5B pass through spaces SP between the light source parts 1 of the 
light source array 5A before reaching the aperture plate 10. 
Where a plurality of the light source arrays 5A and 5B are positioned at 
different locations on the optical axis Z within the light source unit 5, 
an increased number of the light source parts 1 can be arranged in a 
reduced space. For instance, between a structure where a certain number of 
the light source parts 1 are arranged in one plane (i.e., an XY plane) 
which is perpendicular to the optical axis Z as shown in FIG. 2 and a 
structure where the same number of the light source parts 1 are arranged 
in the two different light source arrays 5A and 5B as shown in FIG. 5, 
resulting in smaller pitches of the light beams from the light source unit 
5, resulting in reduction in the sizes of the lenses 41 and 42 which form 
the reduction optical system 40. Although the light source unit 5 is 
formed by the two light source arrays 5A and 5B in this improved 
structure, it is to be noted that the light source unit 5 may consist of 
three or more light source arrays, which is needless to mention. 
B. Second Preferred Embodiment 
FIGS. 6 and 7 are a plan view and a side view, respectively, of a multibeam 
recording apparatus according to a second preferred embodiment of the 
present invention. This multibeam recording apparatus is comprised of a 
light source unit 6 for emitting a plurality of light beams, a reduction 
optical system (imaging optical system) 20, an afocal optical system 30 
and a rotation cylinder 80. A photosensitive material PM is wound around 
the rotation cylinder 80 and the rotation cylinder 80 is rotated in the 
primary scanning direction X while light beams from the light source unit 
6 are swept through the reduction optical system 20 and the afocal optical 
system 30 in synchronism with the rotation of the rotation cylinder 80 in 
the sub scanning direction Y which runs approximately perpendicular to the 
primary scanning direction X. As a result, a desired image is recorded on 
the photosensitive material PM. 
FIG. 8 is a front view of the light source unit 6. In FIG. 8, the light 
source unit 6 consists of a plurality of light source parts 1 which are 
arranged with constant pitches Pa. Each light source part 1 is comprised 
of a semiconductor laser 2 and a collimating lens 3. A light beam from the 
semiconductor laser 2 is collimated by the collimating lens 3 into a 
parallel beam which will be emitted parallel to the optical axis Z (FIGS. 
6 and 7). FIG. 8 shows that the light source parts 1 are arranged to 
partially overlap each other in the primary scanning direction X. This is 
to prevent a split in scanning lines, that is, separation of adjacent 
scanning lines from each other due to mechanical dimensional restraints of 
the light source parts. In addition, to avoid mechanical interference with 
the reduction optical system 20, the light source parts 1 are divided into 
two groups in their arrangement (FIG. 8). 
FIG. 9 is a perspective view of the light source unit 6 and elements 
disposed in the vicinity of the same. In FIG. 9, an aperture plate 11 is 
disposed at the light emitting side of the light source unit 6. In the 
aperture plate 11, apertures 9 are formed in the same arrangement pattern 
as that of the light source parts 1 (FIG. 8). Light beams from the light 
source parts 1 pass through corresponding apertures 9 toward the reduction 
optical system 20 (FIGS. 6 and 7). In this preferred embodiment, the 
aperture plate 11 is located on a focal plane of a parabolic mirror 22. 
FIG. 10 is a view of the reduction optical system 20. Within the reduction 
optical system 20, the parabolic mirror 22 (which has a focal length 
f.sub.22) and a stereographic projection lens 24 are disposed so that 
their focal points coincide with each other at a predetermined point A, 
whereby an afocal optical system is realized. Hence, if light beams 
LB.sub.1 from the light source unit 6 travelling parallel to the optical 
axis Z enter the reduction optical system 20, light beams LB.sub.3 from 
the reduction optical system 20 as well become parallel to the optical 
axis Z. 
The stereographic projection lens 24 is formed by three lenses L.sub.1, 
L.sub.2 and L.sub.3, for example, as shown in FIG. 10. Assume that an 
incident angle of light beams LB.sub.2 entering the stereographic 
projection lens 24 after reflected by the parabolic mirror 22 is .theta.i 
and an image height (i.e., the height of the beams from the optical axis 
Z) is hi', the image height characteristic of the stereographic projection 
lens 24 is expressed as: 
EQU hi'=2.multidot.f.sub.24 .multidot.tan (.theta.i/2) (1) 
where f.sub.24 is a focal length of the stereographic projection lens 24. 
Hence, both the sizes of the apertures 9 of the aperture plate 11 and an 
object height hi from the optical axis Z are reduced by the reduction 
optical system 20 at a magnification m1 (=f.sub.24 /f.sub.22) at the same 
time and imaged at a rear focal plane FP.sub.1 of the stereographic 
projection lens 24. The reason for this is as follows. As shown in FIG. 
10, when the light beams LB.sub.1 parallel to the optical axis Z impinge 
upon the reduction optical system 20 at the object height hi, the light 
beams LB.sub.2 reflected by the parabolic mirror 22 pass the point A, 
which is away from the parabolic mirror 22 by the focal length f.sub.22, 
at the angle .theta.i. Here, due to optical characteristics of the 
parabolic mirror 22, 
EQU tan (.theta.i/2)=hi/(2.multidot.f.sub.22) (2) 
Therefore, substituting Eq. 2 in Eq. 1, 
##EQU1## 
Hence, the light beams LB.sub.1 having equal beam pitches Pa from the light 
source unit 6 are each converged at the rear focal plane FP.sub.1 of the 
stereographic projection lens 24 so that intermediate images of the 
aperture 9 are formed with equal spaces from each other on the rear focal 
plane FP.sub.1. It is only when the aperture plate 11 is disposed at the 
focal plane of the parabolic mirror 22 that images of the apertures 9 are 
formed on the rear focal plane FP.sub.1. If the aperture plate 11 is off 
the focal plane of the parabolic mirror 22, the aperture images will be 
off the rear focal plane FP.sub.1. The amount of the displacement of the 
aperture images is determined by a square of the magnification of the 
reduction optical system 20, i.e., a vertical magnification, as described 
earlier. 
A shown in FIGS. 6 and 7, the afocal optical system 30 is disposed between 
the reduction optical system 20 and the rotation cylinder 80 and is 
comprised of a zoom lens 32 which is formed by lenses L.sub.4 to L.sub.9 
and an afocal optical system 34 which is formed by lenses L.sub.10 and 
L.sub.11. Within the afocal optical system 30, a rear focal plane of the 
zoom lens 32 coincides with a front focal plane of the afocal optical 
system 34 at a plane FP.sub.2, which makes the optical system 30 afocal. A 
front focal plane of the zoom tens 32 coincides with a rear focal plane of 
the stereographic projection lens 24 of the reduction optical system 20 at 
the plane FP.sub.1, while the photosensitive material (i.e., recording 
surface) PM is located at a rear focal plane of the afocal optical system 
34. This allows that intermediate images (i.e., aperture images) which are 
formed at the plane FP.sub.1 are reduced with an appropriate magnification 
by the afocal optical system 30 and focused as aperture images (i.e., beam 
spots) on the photosensitive material PM. 
Thus, in the multibeam recording apparatus according to the second 
preferred embodiment, since the aperture plate 11, the plane FP.sub.1 and 
the photosensitive material PM are located in optical conjugation with 
each other, intermediate images of the apertures 9 of the aperture plate 
11 are formed on the plane FP.sub.1 and further intermediate images (i.e., 
aperture images) are formed on the photosensitive material (i.e., 
recording surface) PM. As result, effects similar to those attainable in 
the first preferred embodiment are achieved. In other words, only if light 
beams from the respective light source parts 1 are parallel to the optical 
axis Z and at least a portion of each light beam is irradiated upon the 
corresponding aperture 9 of the aperture plate 11, inaccurate provision of 
the light source parts 1 in the direction parallel to the optical axis Z 
or the directions X and Y which are perpendicular to the optical axis Z 
will not make it difficult to adjust the light source parts 1 since the 
aperture images are formed at constant positions. 
The foregoing has described a structure where the aperture plate 11 
coincides with the focal plane of the parabolic mirror 22 as the second 
preferred embodiment. However, even if the aperture plate 11 is off the 
focal plane of the parabolic mirror 22, the effects above can be attained 
by arranging the respective elements of the apparatus in such a manner 
that the aperture plate 11 and the photosensitive material PM are in 
optical conjugation similarly to the first preferred embodiment. 
C. Third Preferred Embodiment 
FIGS. 11 and 12 are a perspective view and a plan view, respectively, of a 
multibeam recording apparatus according to a third preferred embodiment of 
the present invention. Optical systems used in this embodiment are 
somewhat similar to those used in the second preferred embodiment except 
for the following three major differences. First, while portions of the 
parabolic mirror 22 which are utilized in the second preferred embodiment 
are those wide portions above and below the optical axis except the 
central portion, the third preferred embodiment uses one portion of the 
parabolic mirror 22. This portion, i.e., a region 22a is off a principal 
axis of the parabolic mirror 22. In general, a parabolic mirror which is 
formed only by such a region 22a is referred to as "off-axis paraboloid 
mirror." Hence, in the description hereinafter, a parabolic mirror of such 
a construction will be referred to as "off-axis paraboloid mirror." 
Second, the third preferred embodiment requires that an optical axis 
Z.sub.1 of the reduction optical system (imaging optical system) 21 is 
displaced from an optical axis Z.sub.2 of the afocal optical system 30 by 
a predetermined distance .DELTA.Y in the sub scanning direction Y. 
Although no practical problem will occur even if the two optical axes 
coincide with each other as in the second preferred embodiment (FIG. 6), 
when the off-axis paraboloid mirror 22a is used, some of the laser beams 
LB.sub.3 from the reduction optical system 21 will not enter the afocal 
optical system 30. In sharp contrast, in the third preferred embodiment, 
since the optical axes are not aligned to each other, the whole afocal 
optical system 30 is involved in directing the laser beams LB.sub.3 toward 
the photosensitive material PM from the reduction optical system 21 as 
shown in FIG. 12. Hence, a reduction in size of the afocal optical system 
30 is attained. 
Third, an arrangement of the light source parts 1 which form a light source 
unit 7 is the same as the arrangement adopted in the first preferred 
embodiment. 
The third preferred embodiment is otherwise almost the same as the second 
preferred embodiment, including the feature that an aperture plate 12 and 
the photosensitive material PM are located in optical conjugation with 
each other. Hence, light beams from the light source parts 1 pass through 
the apertures 9 of the aperture plate 12 and impinge on the off-axis 
paraboloid mirror 22a where they are reflected toward the stereographic 
projection lens 24. The stereographic projection lens 24 images the light 
beams at its rear focal plane FP.sub.1, whereby intermediate images of the 
apertures 9 are formed equidistantly from each other at the rear focal 
plane FP.sub.1. Having been imaged as the intermediate images, the light 
beams enter the zoom lens 32 through a mirror 52 so that further 
intermediate images of the apertures 9 are formed at a rear focal plane 
FP.sub.2 of the zoom lens 32. The light beams then enter the afocal 
optical system 34, which is formed by four lenses L.sub.10, L.sub.15, 
L.sub.16 and L.sub.17, through a mirror 54. The light beams are finally 
converged as aperture images (i.e., beam spots) on the photosensitive 
material PM by the afocal optical system 34. By step feeding a base 51 on 
which the light source unit 7, the aperture plate 12, the reduction 
optical system 20 and the afocal optical system 30 are fixed in the sub 
scanning direction Y, a two-dimensional image is recorded on the 
photosensitive material PM. A change in the image recording density is 
realized by adjusting the magnification of the zoom lens 32 by means of a 
motor 56. 
Thus, similarly to the first and the second preferred embodiments, a slight 
displacement of the light source parts 1 would not prevent aperture images 
from being formed at constant positions and therefore this would not make 
it difficult to adjust the light source parts 1, since the aperture plate 
12 and the photosensitive material PM are positioned in optical 
conjugation with each other in the third preferred embodiment. 
In the third preferred embodiment, the aperture plate 12 is located to 
coincide with the focal plane of the parabolic mirror 22. However, even if 
the aperture plate 12 is displaced from this focal plane, the effects just 
described are attained similarly to the first preferred embodiment only by 
arranging the respective elements of the apparatus in such a manner that 
the aperture plate 12 and the photosensitive material PM are in optical 
conjugation with each other. 
D. Fourth Preferred Embodiment 
FIG. 13 is a plan view of a multibeam recording apparatus according to a 
fourth preferred embodiment of the present invention. This multibeam 
recording apparatus is comprised of a light source unit 8 in which a 
plurality of light source parts 1 are arranged in an arrangement pattern 
which will be described later on a spherical surface E, an aperture plate 
13 in which a plurality of apertures 9 are formed in a spherical surface 
F, an f.theta. lens (imaging optical system) 26 which is formed by three 
lenses L.sub.18 to L.sub.20, an afocal optical system 29 which is formed 
by lenses 27 and 28, and a rotation cylinder 80 for holding the 
photosensitive material PM. 
FIGS. 14 and 15 are a perspective view and a plan view, respectively, 
showing the arrangement (arrangement pattern) of the light source parts. 
The light source parts 1 each consists of a semiconductor laser 2 and a 
collimating lens 3 are arranged two-dimensionally with equal distances 
from each other on the spherical surface E whose center is on a front 
focal plane FP of the f.theta. lens 26. That is, as shown in FIG. 15, the 
light source parts 1 are arranged to partially overlap each other in the 
primary scanning direction X. Further, the principal rays of the light 
beams from the light source parts 1 travel toward the front focal plane FP 
of the f.theta. lens 26. 
The aperture plate 13 is formed in the configuration of the partial 
spherical surface F whose center is on the front focal plane FP of the 
lens 26 as shown in FIG. 13, and located at the light emitting side of the 
light source unit 8. In the aperture plate 13, the apertures 9 are 
arranged in a similar arrangement pattern to the arrangement pattern of 
the light source parts 1 (FIGS. 14 and 15) so as to be each located on an 
imaginary line between the relevant light source part 1 and the front 
focal plane FP of the f.theta. lens 26. In the fourth preferred 
embodiment, though disposed on spherical surfaces because of the 
two-dimensional arrangement of the light source parts 1, the light source 
parts 1 and the aperture plate 13 may be each disposed on a curved surface 
instead when the light source parts 1 are arranged one-dimensionally 
(i.e., in a row or a column). 
As can be seen in FIG. 13, the f.theta. lens 26 and the afocal optical 
system 29 are disposed in this order on the optical axis Z. This 
embodiment requires that a rear focal plane RP of the f.theta. lens 26 
coincides with a front focal plane of the lens 27, a rear focal plane of 
the lens 27 coincides with a front focal plane of the lens 28 and the 
photosensitive material PM is positioned to approximately coincide with a 
rear focal plane of the lens 28. Hence, light beams from the apertures 9 
are converged on the photosensitive material PM through the f.theta. lens 
26 and the afocal optical system 29, thereby images of the apertures 9 
being formed on the photosensitive material PM. As a result, effects as 
described earlier in relation to the precedent preferred embodiments are 
attained. 
E. Fifth Preferred Embodiment 
FIG. 16 is a plan view of a multibeam recording apparatus according to a 
fifth preferred embodiment of the present invention. The multibeam 
recording apparatus according to the fifth preferred embodiment is similar 
to the multibeam recording apparatus according to the fourth preferred 
embodiment except for omission of the afocal optical system 29 which is 
formed by the lenses 27 and 28 and positioning of the photosensitive 
material (i.e., recording surface) PM at the rear focal plane RP of the 
f.theta. lens 26. Hence, in addition to the effects described earlier, the 
fifth preferred embodiment simplifies the structure of the optical systems 
of the multibeam recording apparatus. 
While the invention has been described in detail, the foregoing description 
is in all aspects illustrative and not restrictive. It is understood that 
numerous other modifications and variations can be devised without 
departing from the scope of the invention.