JPH09236741A - Scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning optical system of low cost enabling high-speed scanning without curvature and distortion even when a surface to be scanned is flat. SOLUTION: This optical system is provided with a lens group Gr2 on the object side converging a light beam from a filmy screen 1, a mirror M performing main scanning of the filmy screen 1 by deflecting a light beam transmitted through the lens group Gr2 on the object side and a lens group Gr1 on the image side forming the images of an on-axis light beam, off-axis light beam in the sub-scanning direction (z-axis direction), deflected by the mirror M, together on the image pickup surface of a line CCD 3. A ftanθ optical system is used for the lens group Gr2 on the object side and a main scanning speed is made to be higher as the light beam deflected by the mirror M in the main scanning is separated further away from on-axis to off-axis. The exit pupil of the lens group Gr2 on the object side is made almost coincident with the entrance pupil of the lens group Gr1 on the image side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system, for example, a scanning optical system used in a film scanner or the like capable of capturing an image at high speed.

[0002]

2. Description of the Related Art Conventionally, various film scanners have been proposed. Among them, a mirror scan type film scanner is generally well known. Mirror scan type film scanners are mainly line sensors (for example, line C) in which light receiving elements are arranged in the sub-scanning direction.
CD), a scanning optical system for forming an image of a film on a line sensor, and a mirror that swings and rotates for main scanning.

In the above film scanner, since the film screen, which is the surface to be scanned, is flat, the optical path length between the mirror and the surface to be scanned changes as the mirror rotates when scanning the film screen. There is a problem that it will end up. In order to solve such a problem, Japanese Patent Publication No. 62-20526 discloses that a rotationally asymmetric imaging optical system in which Petzval sum, distortion aberration coefficient, etc. are defined is provided between a mirror and a plane to be scanned. A scanning device has been proposed in which the above optical path length is corrected so that a flat surface to be scanned is scanned at high speed without bending or distortion.

[0004]

[Problems to be Solved by the Invention] However, JP-B-62-205
The rotationally asymmetric image forming optical system used in the scanning device of No. 26 is an expensive optical system having a surface shape that is difficult to manufacture, so that there is a problem that the cost of the scanning device increases. Also, because the size of the mirror is inevitable,
It is difficult to rotate the mirror at high speed, and the film 1
There is a problem that it takes 10 seconds to several minutes to capture the frame image.

The present invention has been made in view of these points, and an object thereof is to provide a low-cost scanning optical system that enables high-speed scanning without curvature or distortion even if the surface to be scanned is flat. To provide.

[0006]

In order to achieve the above object, a scanning optical system of the present invention deflects light passing through an object side lens group for condensing light from an object and the object side lens group. A mirror for performing main scanning for picking up an image of an object, and an image-side lens group for forming both on-axis light and off-axis light in the sub-scanning direction, which are deflected by the mirror, on an image pickup surface. In the scanning optical system, an ftan θ optical system is used as a lens group of the object side lens group and the image side lens group whose optical path changes in the main scanning, and the light deflected by the mirror in the main scanning is an axis. The main scanning speed increases as the distance from the top to the off-axis increases,
Further, the exit pupil of the object side lens group and the entrance pupil of the image side lens group are substantially matched.

An object-side lens group that collects light from an object, a mirror that performs main scanning for imaging an object by deflecting light that has passed through the object-side lens group, and sub-scanning that is deflected by the mirror In the scanning optical system including the image side lens group that forms both on-axis light and off-axis light in the image direction on the imaging surface, the optical path changes in the main scan of the object side lens group and the image side lens group. When the ftan θ optical system is used as the lens group, the projection changes as the optical path changes when the main scanning is performed. That is, fta
In the nθ-based projection method, the further the light deflected by the mirror is from the on-axis to the off-axis in the main scanning direction, the light entering the lens group whose optical path changes is more off-axis than the light to be originally incident. Since it becomes light, distortion occurs in the image in the main scanning direction. By correcting the scanning speed by the mirror, it is possible to eliminate the change in the projection in the main scanning direction.
Therefore, in the present invention, the main scanning speed is increased as the light deflected by the mirror moves away from the on-axis to off-axis so that the image is not distorted in the main scanning direction.

On the other hand, also in the sub-scanning, as the light deflected by the mirror becomes farther from the on-axis to the off-axis in the main-scanning direction, the light incident on the lens group whose optical path changes is more than the light originally supposed to enter. Since the light is off-axis, the image is distorted in the sub-scanning direction. If the image is one-dimensionally corrected in the sub-scanning direction, the change in the projection in the sub-scanning direction can be eliminated. For example, when a line sensor such as a line CCD is used, the image is corrected in the arrangement direction of the light receiving elements on the imaging surface (that is, the sub-scanning direction), and thus the image is sub-scanned by the processing of the captured image. It is easy to electrically correct directional distortion.

In the present invention, to make the exit pupil of the object side lens group and the entrance pupil of the image side lens group substantially coincide with each other means that the exit pupil of the object side lens group and the image side lens have substantially the same pupil diameter. It means that the entrance pupil of the group is located at substantially the same position. According to the above definition, in an optical system in which the optical axes of the object-side lens group and the image-side lens group are coincident with each other, regarding the configuration in which the exit pupil of the object-side lens group and the entrance pupil of the image-side lens group coincide with each other, (1 ) When the two pupils have substantially the same pupil diameter but are not located at substantially the same position, (2) the two pupils are located at substantially the same position as each other but have substantially the same pupil diameter. If not, (3) if the two pupils have different pupil diameters and different positions, the details will be described in the order of (4) the present invention.

In the case of the configuration (1), since the positions of the two pupils on the optical axis are not substantially the same position, for example, when the axial light is emitted as divergent light from the object side lens group, A part of the upper light cannot pass through the entrance pupil of the image side lens group, resulting in a loss of light quantity. On the other hand, in the case where axial light is emitted as convergent light from the object side lens group, the image side lens group has a large area in which light does not pass, and the entire optical system becomes large. If the exit pupil of the object-side lens group and the entrance pupil of the image-side lens group are not at substantially the same position, all off-axis light (that is, light having an image height) that has passed through the exit pupil of the object-side lens group It cannot enter the entrance pupil of the image side lens group.

In the case of the configuration (2), since the exit pupil of the object side lens group and the entrance pupil of the image side lens group are located at substantially the same position, the pupil having the smaller pupil diameter is substantially the same. Will have the effect of regulating the. Therefore, when the exit pupil diameter of the object side lens group is larger than the entrance pupil diameter of the image side lens group,
Not all light on the object side can be transmitted to the image side regardless of on-axis light and off-axis light. On the contrary, when the entrance pupil diameter of the image side lens group is larger than the exit pupil diameter of the object side lens group, the image side lens group has a large area in which light does not pass, and the entire optical system is It becomes large.

In the case of the configuration (3), the exit pupil diameter of the object side lens group and the entrance pupil diameter of the image side lens group are appropriately set so that the axial light is transmitted from the object side lens group to the image side lens group without omission. Can be specified. However, even in this case, if the exit pupil of the object side lens group and the entrance pupil of the image side lens group are not at substantially the same position, as in the case of (1), the exit pupil of the object side lens group is passed. Not all off-axis light can enter the entrance pupil of the image side lens group.

On the other hand, in the present invention of (4), since the exit pupil of the object side lens group and the entrance pupil of the image side lens group are made to substantially coincide with each other, not only axial light but also axial light External light can also be transmitted from the object side lens group to the image side lens group without fail.

For example, in a laser scanning optical system used in a printer or the like, since on-axis light and off-axis light are used together in the main scanning direction, a mirror is provided near the entrance pupil position of the lens group on the image side. Will be placed. However, since off-axis light in the sub-scanning direction is not used (that is, it does not have an image height in the sub-scanning direction), the pupils of the lens groups corresponding to the object-side lens group and the image-side lens group in the present invention are not changed. No need to match.
On the other hand, in the present invention, both the on-axis light and the off-axis light in the sub-scanning direction deflected by the mirror are imaged on the image pickup surface by the image side lens group (that is, the image height is in the sub-scanning direction). ), As described above, unless the exit pupil of the object side lens group and the entrance pupil of the image side lens group are substantially aligned, all off-axis light that has passed through the exit pupil of the object side lens group is imaged. The light cannot enter the entrance pupil of the side lens group.

When the exit pupil of the object side lens group and the entrance pupil of the image side lens group are made to substantially coincide with each other as described above, the object side lens group and the image side lens group become one lens system sharing a pupil. . When an ordinary optical system is used, an object is scanned while drawing an arc when the mirror is rotated, so that the image plane is curved. However, when the exit pupil of the object-side lens group and the entrance pupil of the image-side lens group are made to substantially coincide with each other as described above, field curvature does not occur in each of the object-side lens group and the image-side lens group. The curvature of the image plane does not occur in the entire scanning optical system. Since it is easy to correct the field curvature for each of the object-side lens group and the image-side lens group, it is not necessary to use an optical system having a complicated surface shape. For example, only a rotationally symmetric spherical system can be used. An object side lens group and an image side lens group can be configured. This rotationally symmetric spherical system is inexpensive and easy to manufacture.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning optical system embodying the present invention will be described below with reference to the drawings. In each figure, x
The axis, the y-axis, and the z-axis indicate axes orthogonal to each other. First, FIG. 1 shows a basic configuration of a scanning optical system common to the embodiments of the present invention. This scanning optical system is mainly a mirror scanning type scanning optical system including an image side lens group Gr1, a mirror M, and an object side lens group Gr2 in order from the image side. A film screen 1 is arranged at a fixed position on the object side of the scanning optical system during image pickup, and a line CCD 3 and a prism 2 are arranged on the image side of the scanning optical system.
The prism 2 is a color separation prism used when three-plate type color separation is performed, and is unnecessary when color separation is not performed.

The object side lens group Gr2 (the optical axis of which is parallel to the x axis) collects the light from the film screen 1. In FIG. 1, RB is the axial light in the main / sub scanning direction, RA is the object height Z (+) in the sub scanning direction,
The image height Z '(-) is off-axis light, and RC is the object height Z (-) and image height Z' (+) off-axis light in the sub-scanning direction. The planar mirror M performs main scanning of the film screen 1 by deflecting the light that has passed through the object side lens group Gr2. The deflection is performed by rotating the mirror M, and the main scanning of the film screen 1 is performed in the y-axis direction. Image side lens group Gr1
(In this portion, the optical axis is parallel to the y-axis.) Indicates that both the on-axis light and the off-axis light in the sub-scanning direction (z-axis direction) deflected by the mirror M are on the imaging surface of the line CCD 3. Form an image. The image formed on the image pickup surface of the line CCD 3 is a line-shaped image in the sub-scanning direction (z-axis direction) on the film screen 1, and is captured by the line CCD 3 line by line as image information.

The lenses constituting the object side lens group Gr2 have a circular yz cross section so as to cover the light flux in both the y-axis and z-axis directions. In contrast,
The image-side lens group Gr1 needs to cover the light beam only in the sub-scanning direction (z-axis direction), which is the light-receiving element arrangement direction of the line CCD 3, so that the xz section has an oval shape that is long in the z-axis direction. . By thus forming the image-side lens group Gr1 in an oval shape, it is possible to save space in the scanning device.

In this scanning optical system, the line CCD 3 is used as the image pickup section, but another line sensor may be used as the image pickup section instead of the line CCD 3, and a photosensitive drum is used as the image pickup section. Good. When the photoconductor drum is used, the generatrix thereof is arranged so as to be parallel to the sub-scanning direction, and the rotation of the photoconductor drum is controlled by the mirror
Synchronize with the rotation of.

Although this scanning optical system is applied to a film scanner, the scanning optical system of the present invention can be applied to other scanning devices. For example, instead of the line CCD 3, a device (for example, an LED array or a transmissive LCD panel) that emits light including image information is arranged, and instead of the film screen 1, the light including image information is received and read, Light receiving device for recording (Area C
A CD or a planar photoconductor) may be provided. In this case, the image side lens group Gr1 becomes the object side lens group, and the object side lens group Gr2 becomes the image side lens group.

Next, the image distortion caused by the difference in the projection method of the object side lens group Gr2 will be described. FIG.
(A) shows a film image on the film screen 1 (FIG. 1), in which Ymax is a main scanning range and Zmax is a sub-scanning range. 2B to 2D are image pickup surfaces of the line CCD 3 when the main scanning of the film screen 1 is performed by rotating the mirror M at a constant angular velocity using the object side lens group Gr2 having different projection methods. Fig. 3 shows an image of a film image {Fig. 2 (A)} formed at a position. The image shown in FIG. 2B is obtained when an fθ lens is used as the object side lens group Gr2, and the image shown in FIG. 2C is the object side lens group Gr2.
It is obtained when the fsin θ lens is used as shown in FIG.
The image shown in is obtained when the ftan θ lens is used as the object side lens group Gr2.

In the fθ method {FIG. 2 (B)}, the main scanning direction (y
Since the intervals in the axial direction) are equal, it is not necessary to correct the rotation speed of the mirror M, but it is necessary to correct the two-dimensional image in both the main and sub scanning directions (y and z axis directions). fs
In the in θ method {Fig. 2 (C)} and the ftan θ method {Fig. 2 (D)},
Since the interval in the main scanning direction is different, it is necessary to correct the rotation speed of the mirror M, but the necessary image correction is one-dimensional. However, in the case of the fθ method and the fsin θ method, since the curved distortion occurs in the main scanning direction (y-axis direction), all the line-shaped images on the corresponding film screen 1 are projected on the imaging surface of the line CCD 3. Is difficult.

In this scanning optical system, an ftan θ optical system is used as the object side lens group Gr2. ftan
In the case of the θ method, when the main scanning of the film screen 1 is performed by deflecting the light by the mirror M, the object side lens group Gr
The optical path of 2 changes, and the projection changes accordingly. That is, in the ftan θ projection method, the light deflected by the mirror M is in the main scanning direction (y-axis direction) as shown in FIG.
As the distance from the on-axis to the off-axis is increased, the light incident on the object side lens group Gr2 becomes more off-axis than the light originally supposed to enter, so that the image is distorted in the main scanning direction. By correcting the scanning speed by the mirror M, the change in the projection in the main scanning direction can be eliminated, so that in this scanning optical system, the main scanning is performed as the light deflected by the mirror M moves away from on-axis to off-axis. By increasing the speed,
The image is not distorted in the main scanning direction. In this way, high-speed scanning without distortion in the main scanning direction becomes possible.

On the other hand, also in the sub-scan, as the light deflected by the mirror M deviates from the on-axis to the off-axis in the main scanning direction, the light incident on the object side lens group Gr2 is more axial than the light to be originally incident. Since the light is outside light, the image is distorted in the sub-scanning direction. By performing a one-dimensional correction in the sub-scanning direction on the image, it is possible to eliminate the change in the projection in the sub-scanning direction. Therefore, in this scanning optical system, the distortion of the image in the sub-scanning direction is caused by processing the captured image. Is corrected electrically. Since the correction of the image in the sub-scanning direction is the correction in the arrangement direction (z-axis direction) of the light receiving elements of the line CCD 3, the correction is easy. In this way,
High-speed scanning without distortion in the sub-scanning direction is possible.

In this scanning optical system, the deflection for the main scanning is performed by the rotation of the mirror M as in the case of the ordinary mirror scanning type scanning optical system, but the mirror M is not limited to the oscillating rotation. That is, the object side lens group Gr
Since a space that allows the mirror M to rotate all around is provided between the lens 2 and the image-side lens group Gr1, by rotating the mirror M all around, a biased load is applied to the bearing portion of the mirror M. You can prevent it from continuing. The full rotation of the mirror M may be performed, for example, every time the main scanning is performed once or every predetermined number of times the main scanning is performed, and at the time of startup (that is, when the power of the scanning device is turned on). ).

By reducing the uneven load applied to the bearing portion of the mirror M as described above, problems such as uneven wear of the bearing portion of the mirror M or partial oil shortage may occur. Can be prevented. Further, a drive device for swinging and rotating the mirror M (for example, a galvano device)
Since it is possible to rotate the mirror M all the way around with a driving device (for example, a driving device including a DC motor) which is cheaper and has a simpler structure, it is possible to reduce the cost of the scanning device. In addition, the configuration can be simplified.

Next, the detailed configuration of the scanning optical system shown in FIG. 1 will be described with reference to three embodiments. 3 to 5, FIG. 6 to FIG. 8 and FIG. 9 to FIG. 11 are xy cross-sectional views corresponding to the first to third embodiments, respectively, and FIGS. 3, 6 and 9 are mirrors. Rotation angle (that is, mirror swing angle) θ = 45 °
(At this time, the object height is Y = 0.), And FIGS. 4, 7 and 10 show the optical path at the mirror rotation angle θ = 48.5 °, and FIGS. 11 and 12 show the optical path at the mirror rotation angle θ = 41.5 °. Further, in the lens configuration diagrams of FIGS. 3, 6 and 9, Si (i = 1,2,3, ...) is an object.
The i-th surface counted from the (film screen 1) side is shown.

<< First Embodiment >> In the first embodiment shown in FIGS. 3 to 5, each of the image side lens group Gr1 and the object side lens group Gr2 is composed of nine rotationally symmetric spherical lenses. Therefore, a symmetrical type configuration is adopted through the mirror M, which is advantageous for aberration correction. Further, the image side lens group Gr1 is
The xz section has an oval shape. As previously mentioned,
By making the image-side lens group Gr1 an oval shape, it is possible to save space in the scanning device. In addition, in FIGS. 3 to 5, θ = 45 ° ± 3.5 centered on θ = 45 ° (FIG. 3)
The object height Y corresponding to ° is the main scanning range Ymax.

In the first embodiment, the object side lens group Gr
Since the exit pupil of No. 2 and the entrance pupil of the image-side lens group Gr1 substantially match, the on-axis light and off-axis light that have passed through the exit pupil of the object-side lens group Gr2 are all image-side lens groups. G
The light enters the entrance pupil of r1 and is transmitted from the object side lens group Gr2 to the image side lens group Gr1. Therefore, both the on-axis light and the off-axis light in the sub-scanning direction deflected by the mirror M are line CCD 3 by the image side lens group Gr1.
An image is formed on the imaging surface of.

As described above, when the exit pupil of the object side lens group Gr2 and the entrance pupil of the image side lens group Gr1 are made to substantially coincide with each other,
The object side lens group Gr2 and the image side lens group Gr1 form one lens system that shares the pupil. The object-side lens group Gr2 and the image-side lens group Gr1 are composed of only rotationally symmetric spherical systems as described above, and the field curvatures thereof are well corrected. Therefore, the curvature of the image plane does not occur in the entire scanning optical system. As described above, the object-side lens group Gr2 and the image-side lens group Gr2 are formed by a rotationally symmetric spherical system that is inexpensive and easy to manufacture.
By configuring No. 1, the cost reduction of the scanning device can be achieved. Further, since the scanning optical system has a simple spherical system, it is easy to cope with the increase in the rotation speed of the mirror M, and as a result, the image capture of one frame of 135 film is 0.2 to 1. It can be done in about a second.

Since the mirror M is arranged in the vicinity of the above-mentioned substantially matched pupil, the mirror size is smaller than that of the conventional one, but from the object side lens group Gr2 to the image side lens group Gr1. All light is transmitted. Even when the light is deflected by the mirror M arranged in the vicinity of the matched pupils, the field curvatures of the respective lens groups Gr1 and Gr2 are properly corrected, and therefore, they are formed on the image pickup surface of the line CCD 3. No curvature occurs in the image plane formed. Therefore, even if the film screen 1, which is the surface to be scanned, is flat, high-speed scanning without curvature is possible. Further, in the mirror M, only the central portion is a reflecting surface, and the outer peripheral portion thereof is a light shielding surface (may be a transmitting surface). Therefore, the mirror M functions as a diaphragm that regulates the incident light flux with the size and shape of the reflecting surface. Although this scanning optical system has a configuration in which parallel light is incident on the mirror M, it may be configured so that convergent light and divergent light are incident.

By the way, when the main scanning of the film screen 1 is performed by the mirror M, the optical path in the object side lens group Gr2 changes. That is, in the main scanning direction, even if the light that enters the object-side lens group Gr2 is off-axis light, it will enter the image-side lens group Gr1 as axial light. However, since the object-side lens group Gr2 and the image-side lens group Gr1 have the imaging performance as independent front diaphragm lenses having the mirror M as the diaphragm, they are sufficient imaging performance as the entire scanning optical system. Is obtained.

<Second Embodiment> In the second embodiment shown in FIGS. 6 to 8, the image side lens group Gr1 and the object side lens group Gr2 each consist of nine rotationally symmetric spherical lenses. Therefore, it has a substantially symmetrical structure which is advantageous for aberration correction via the mirror M. Further, since the prism 2 is provided on the line CCD 3 side, the configuration is suitable for performing color separation.

The point where the exit pupil of the object side lens group Gr2 and the entrance pupil of the image side lens group Gr1 are substantially matched is the same as in the first embodiment described above, and the effect is also the same. Further, since the object side lens group Gr2 and the image side lens group Gr1 have the image forming performance as independent front diaphragm lenses in which the diaphragm A is the front diaphragm, they are the same as in the first embodiment. , Sufficient imaging performance can be obtained as the entire scanning optical system.

The feature of the second embodiment is that an aperture stop A is arranged in the vicinity of the substantially matched pupil, and the object side lens group Gr2
The mirror M is arranged between the aperture and the diaphragm A. When main scanning of the film screen 1 is performed by deflecting light by the mirror M, when the mirror M acts as a diaphragm that regulates the light flux as in the first embodiment, the angle between the mirror M and the light flux becomes smaller. The projection changes with the change. The amount of light incident on the image-side lens group Gr1 changes due to the influence of this change in projection. For example, as the mirror rotation angle θ increases, the amount of light received by the mirror M increases, and conversely, as the mirror rotation angle θ decreases, the amount of light received by the mirror M decreases. Therefore, light amount unevenness occurs in the image captured by the line CCD 3.

According to the configuration of the second embodiment, since the mirror M having the entire reflecting surface is arranged between the object side lens group Gr2 and the diaphragm A, the light flux is not restricted by the mirror M, The light flux is regulated by the diaphragm A. As a result, the amount of light incident on the image side lens group Gr1 becomes constant, and deterioration of the illuminance distribution (that is, the illuminance distribution on the imaging surface of the line CCD 3) is prevented. If the diaphragm A is arranged between the object side lens group Gr2 and the mirror M, vignetting will occur in the light beam in the main scanning.

Since the image side lens group Gr1 is an optical system which is substantially telecentric on the image side, a double plate type (for example,
It is suitable when a line sensor such as a (three-plate type) line CCD is used as an imaging unit. This is because the more telecentric the image side lens group Gr1 is on the image side, the better the matching of the angular characteristics of the dichroic film of the multicolor separation prism (for example, the three color separation prism). Further, when the incident light to the object side lens group Gr2 has an angle with respect to the optical axis, the illuminance distribution deteriorates according to the cosine fourth law, but the object side lens group Gr2 is substantially telecentric to the object side. Since it is an optical system, it is advantageous in preventing the deterioration of the illuminance distribution. The same applies to the first embodiment in that a telecentric system is used for the image-side and object-side lens groups Gr1 and Gr2.

<< Third Embodiment >> The third embodiment shown in FIGS. 9 to 11 has the same basic structure and effect as the above-described second embodiment, but the first embodiment is the same as the first embodiment. The configuration is more practical than that of the second embodiment. The number of lenses is small, and the image side lens group Gr1 is composed of seven rotationally symmetric spherical lenses, and the object side lens group Gr1.
2 comprises 6 rotationally symmetric spherical lenses. Further, since the line CCD 3 side is provided with the prism 2 and the cover glass, the configuration is more suitable for color separation.

[0039]

EXAMPLES The configuration of the scanning optical system embodying the present invention will be described more specifically below with reference to construction data and the like. Examples 1 to 3 given here as examples
Are examples corresponding to the above-described first to third embodiments (FIGS. 3 to 5, FIGS. 6 to 8, and FIGS. 9 to 11, respectively). Then, in the construction data of each example, Si (i = 1,2,3, ...) is the i-th surface counted from the object side, ri (i = 1,2,3, ...) is The radius of curvature of the i-th surface Si counted from the object side, di (i = 1,2,3, ...) indicates the i-th axial upper surface distance counted from the object side, and Ni (i = 1 , 2, 3, ...) Shows the refractive index (Nd) of the i-th lens with respect to the d-line counting from the object side. Further, the focal length f of the entire system and the effective F number EFFNO on the image side when the mirror rotation angle θ = 45 ° (at this time, the object height Y = 0) are also shown. Further, Table 1 shows the mirror rotation angle θ (°) and the object height Y (mm) corresponding to the mirror rotation angle θ in each example.

Example 1

Example 2 f = 68.239, EFFNO = 3.49 [plane] [radius of curvature] [interval of axial upper surface] [refractive index] S1 r1 = -34.552 d1 = 4.000 N1 = 1.51680 S2 r2 = -1136.364 d2 = 10.000 N2 = 1.61659 S3 r3 = -135.073 d3 = 3.000 S4 r4 = -82.721 d4 = 10.000 N3 = 1.67000 S5 r5 = -50.877 d5 = 0.620 S6 r6 = -1145.869 d6 = 10.000 N4 = 1.67000 S7 r7 = -125.677 d7 = 0.620 S8 r8 = 85.317 d8 = 8.560 N5 = 1.67000 S9 r9 = 451.284 d9 = 0.620 S10 r10 = 46.069 d10 = 12.000 N6 = 1.51680 S11 r11 = -119.753 d11 = 3.750 N7 = 1.80518 S12 r12 = 47.788 d12 = 9.000 S13 r13 = -41.217 d13 = 4.000 N8 = 1.67000 S14 r14 = -62.455 d14 = 4.000 S15 r15 = -93.171 d15 = 2.500 N9 = 1.80518 S16 r16 = -47.299 d16 = 18.000 S17 r17 = ∞ (Mirror M) d17 = 17.000 S18 r18 = ∞ (Aperture A ) d18 = 1.000 S19 r19 = 42.128 d19 = 1.550 N10 = 1.84666 S20 r20 = 99.150 d20 = 8.990 S21 r21 = 200.000 d21 = 2.480 N11 = 1.67000 S22 r22 = 38.462 d22 = 5.580 S23 r23 = -22.073 d23 = 2.325 N12 = 1.80518 S24 r24 = 217.771 d24 = 7.440 N13 = 1.51680 S25 r25 = -28.733 d25 = 0.384 S26 r26 = -431.654 d26 = 5.307 N14 = 1 .67000 S27 r27 = -35.664 d27 = 0.384 S28 r28 = 96.281 d28 = 6.200 N15 = 1.67000 S29 r29 = 2927.315 d29 = 0.384 S30 r30 = 37.345 d30 = 6.200 N16 = 1.67000 S31 r31 = 44.920 d31 = 1.860 S32 r32 = 45.893 d32 = 6.200 N17 = 1.58144 S33 r33 = 123.964 d33 = 2.480 N18 = 1.58913 S34 r34 = 32.678 d34 = 30.000 S35 r35 = ∞ d35 = 20.600 N19 = 1.74400 (Prism 2) S36 r36 = ∞ d36 = 0.800 N20 = 1.51680 (Prism 2) S37 r37 = ∞

Example 3 f = 88.399, EFFNO = 4.99 [plane] [radius of curvature] [axis upper surface spacing] [refractive index] S1 r1 = -49.542 d1 = 4.000 N1 = 1.61659 S2 r2 = 844.495 d2 = 10.000 S3 r3 = -630.064 d3 = 8.000 N2 = 1.61800 S4 r4 = -83.652 d4 = 1.000 S5 r5 = 186.095 d5 = 8.000 N3 = 1.61800 S6 r6 = -186.302 d6 = 0.620 S7 r7 = 70.451 d7 = 7.000 N4 = 1.61800 S8 r8 = 312.890 d8 = 2.620 S9 r9 = 36.382 d9 = 8.000 N5 = 1.69100 S10 r10 = 76.584 d10 = 4.000 N6 = 1.66446 S11 r11 = 26.274 d11 = 33.000 S12 r12 = ∞ (Mirror M) d12 = 12.000 S13 r13 = ∞ (Aperture A) d13 = 4.500 S14 r14 = 30.560 d14 = 5.500 N7 = 1.78831 S15 r15 = -51.112 d15 = 2.200 N8 = 1.54072 S16 r16 = 143.776 d16 = 8.000 S17 r17 = -33.178 d17 = 3.000 N9 = 1.75520 S18 r18 = 30.510 d18 = 7.200 S19 r19 = -63.595 d19 = 5.000 N10 = 1.68150 S20 r20 = -36.559 d20 = 1.000 S21 r21 = 79.252 d21 = 9.000 N11 = 1.71700 S22 r22 = -34.900 d22 = 3.800 S23 r23 = -34.526 d23 = 2.800 N12 = 1.61659 S24 r24 = 107.174 d24 = 3.000 S25 r25 = 90.113 d25 = 7.000 N13 = 1.69680 S26 r26 = -90.481 d26 = 16.000 S27 r27 = ∞ d2 7 = 20.000 N14 = 1.74400 (prism 2) S28 r28 = ∞ d28 = 2.400 N15 = 1.51680 (prism 2) S29 r29 = ∞ d29 = 0.500 S30 r30 = ∞ d30 = 0.800 N16 = 1.51680 (cover glass) S31 r31 = ∞

[0043]

[Table 1]

[0044]

As described above, according to the present invention, since the exit pupil of the object side lens group and the entrance pupil of the image side lens group are made to substantially coincide with each other, the surface to be scanned is flat. Even if it exists, high-speed scanning without curvature is possible. Further, since the object side lens group and the image side lens group can be constituted only by a rotationally symmetric spherical system which is inexpensive and easy to manufacture, it can be realized at a low cost. Therefore, by using the scanning optical system according to the present invention, it is possible to effectively reduce the cost of the scanning device. Further, since the ftan θ optical system is used as the object side lens group and the main scanning speed becomes faster as the light deflected by the mirror in the main scanning moves away from on-axis to off-axis, high-speed scanning without distortion Is possible.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a basic configuration of an embodiment according to the present invention.

FIG. 2 is a diagram for explaining the relationship between the projection method of the object side lens group and the image plane in the embodiment of FIG.

FIG. 3 is a mirror rotation angle θ according to the first mode for embodying the present invention (embodiment 1).
Lens configuration diagram when = 45 °.

FIG. 4 is a mirror rotation angle θ according to the first mode for embodying the present invention (embodiment 1).
Lens configuration diagram when = 48.5 °.

FIG. 5 is a mirror rotation angle θ according to the first mode for embodying the present invention (embodiment 1).
Lens configuration diagram when = 41.5 °.

FIG. 6 is a mirror rotation angle θ according to the second mode for embodying the present invention (embodiment 2).
Lens configuration diagram when = 45 °.

FIG. 7 shows a mirror rotation angle θ according to the second mode for embodying the present invention (embodiment 2).
Lens configuration diagram when = 48.5 °.

FIG. 8 is a mirror rotation angle θ according to the second mode for embodying the present invention (embodiment 2).
Lens configuration diagram when = 41.5 °.

FIG. 9 shows a mirror rotation angle θ of the third mode for embodying the present invention (embodiment 3).
Lens configuration diagram when = 45 °.

FIG. 10 is a lens configuration diagram of a third embodiment (Example 3) when a mirror rotation angle θ = 48.5 °.

FIG. 11 is a lens configuration diagram of the third embodiment (Example 3) when the mirror rotation angle θ = 41.5 °.

[Explanation of symbols]

 1 ... Film screen 2 ... Prism 3 ... Line CCD Gr1 ... Image side lens group Gr2 ... Object side lens group M ... Mirror A ... Aperture

Claims (1)

[Claims] 1. An object-side lens group that collects light from an object, and a mirror that performs main scanning for imaging an object by deflecting light that has passed through the object-side lens group.
A scanning optical system comprising: an image-side lens group that forms both on-axis light and off-axis light in the sub-scanning direction, which are deflected by the mirror, on an imaging surface, the object-side lens group, the image Among the side lens groups, an ftan θ optical system is used as a lens group whose optical path changes in the main scanning, and the main scanning speed is increased as the light deflected by the mirror in the main scanning is deviated from on-axis to off-axis, The scanning optical system is characterized in that an exit pupil of the object side lens group and an entrance pupil of the image side lens group are substantially aligned with each other.