JP2006352761A - Optical unit, image reading unit, image reading apparatus, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce noise light in an optical unit comprised of two lens units, and to obtain an excellent image in an image reading apparatus or the like without read image deterioration, S/N reduction, MTF deterioration and color reproducibility deterioration. <P>SOLUTION: A lens 21 is comprised of two lens units of front group lenses 23 and rear group lenses 24, and a CCD 22 is located behind the rear group lenses 24. If there is a gap 28 between the front group lenses 23 and the rear group lenses 24 in an assembled state, light is made incident from the gap 28 and trouble may occur. In order to cut off noise light or flare light, therefore, a tubular light shielding member 30 is disposed over the inner side of the front group lenses 23 and the inner side of the rear group lenses 24. The light shielding member 30 prevents external light from entering from the gap 28 between the front group lenses 23 and the rear group lenses 24. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical unit, an image reading unit, an image reading apparatus, and an image forming apparatus using these, and more particularly to a light-shielding technique for a two-divided lens and an application of this technique.

  For example, as shown in FIG. 1, an image reading apparatus or an image reading unit used in an image forming apparatus often employs a lens 21 and a photoelectric conversion element (hereinafter, CCD) 22. The lens 21 includes two lens units, a front group lens 23 and a rear group lens 24, and the CCD 22 is positioned behind the rear group lens 24. In the image reading apparatus, a lens block 25 is provided to adjust and bond the focus and magnification. The front group lens 23, the rear group lens 24, and the CCD 22 are assembled with an assembly adjustment jig (not shown). The position of the lens block 25 is adjusted and determined. In general, the lens block 25 is then adhered and fixed via the holding members 26. In the figure, reference numeral 27 denotes a substrate of the CCD 22. Reference numeral 29 denotes an opening provided in the lens block 25.

  That is, in recent years, the pixel size of the CCD 22 has been reduced to 10 μm, 7 μm, and 4.7 μm with the progress of technology. Along with this, the amount of light irradiated to the CCD 22 also decreases, and if the amount of noise light is the same as before, the ratio of the noise light to the relatively effective image forming light increases, and various problems occur. It tends to come out easily. Further, in a color 3-line CCD as compared with a black-and-white CCD, a slight change in noise light breaks the RGB balance, and there is a tendency that a problem is more likely to occur and a sensitive reaction occurs. As the pixel size of the CCD 22 becomes smaller, it is necessary to strictly adjust the distance between the lens groups. In order to more precisely adjust the distance between the lens groups, a technique for dividing the lens group into two as described above has been proposed and implemented.

  By the way, in the optical unit and the image reading apparatus configured as described above, if there is a gap 28 between the front group lens 23 and the rear group lens 24, light enters from there and the above-described problems occur. As a result of the inventors' research. That is, stray light (flare light) that does not pass through the front lens group 3 and the rear lens group 4 is incident on the CCD 2, and as optical noise, the read image is deteriorated, the S / N is decreased, the MTF is deteriorated, and the color reproducibility is deteriorated. Will be generated.

  Therefore, the present invention has a technical problem of reducing noise light in an optical unit having a basic configuration including two lens units of a front lens group and a rear lens group. By using such an optical unit, a read image can be obtained. It is an object of the present invention to provide an image reading apparatus and an image forming apparatus capable of obtaining a good image without deterioration, S / N reduction, MTF deterioration, and color reproducibility deterioration.

  An optical unit according to a first aspect of the present invention includes a first lens unit, a second lens unit, a lens block for determining the positions of the first and second lens units, the first, It has a light-shielding member that shields light between the second lens units.

  According to the second aspect of the present invention, in the optical unit of the first aspect, the optical unit includes photoelectric conversion means for photoelectrically converting light that has passed through the first lens unit and the second lens unit.

  According to a third aspect of the invention, in the optical unit of the second aspect, the optical unit includes a substrate on which a circuit for controlling an input / output signal of the photoelectric conversion means is mounted.

  According to the fourth aspect of the present invention, in the optical unit according to any one of the first to third aspects, the light shielding member covers a gap existing between the first and second lens units from the outside. It is characterized by.

  According to the fifth aspect of the present invention, in the optical unit of the fourth aspect, the light shielding member is divided into two or more along the optical axis direction of the first and second lens units. It is characterized by being.

  According to the sixth aspect of the present invention, in the optical unit of the fourth or fifth aspect, the light shielding member is cylindrical.

  According to the seventh aspect of the present invention, in the optical unit according to any one of the first to third aspects, the light-shielding member extends one body portion of the first or second lens unit to the other side. The lens unit on the other side covers at least the end on the gap side from the outside.

  According to the eighth aspect of the present invention, in the optical unit of the seventh aspect, the light shielding member is cylindrical.

  According to the ninth aspect of the present invention, in the optical unit of the fourth aspect, the light shielding member is provided so as to shield light even between the second lens unit and the photoelectric conversion means.

  According to the tenth aspect of the present invention, in the optical unit of the ninth aspect, the light shielding member is a cover.

  According to the eleventh aspect, in the optical unit according to any one of the first to tenth aspects, the first and second lens units are slidably mounted on the lens block in the optical axis direction. It is characterized by.

  An image reading apparatus according to a twelfth aspect of the present invention is characterized by using any one of the optical units according to the first to eleventh aspects.

  An image forming apparatus according to a thirteenth aspect of the present invention includes the optical unit according to any one of the first to eleventh aspects.

  An image forming apparatus according to a fourteenth aspect of the present invention uses the image reading apparatus according to the thirteenth aspect.

  An image reading unit according to a fifteenth aspect of the present invention includes an optical element having a transmission surface through which a light beam passes, a photoelectric conversion member that receives and photoelectrically converts the light beam that has passed through the transmission surface, and input / output of the photoelectric conversion member. In an image reading unit including a substrate on which a circuit for controlling signals is mounted, the optical element includes two lens units, a front group lens unit and a rear group lens unit, and the position of each of these lens units and the photoelectric conversion A lens block for adjusting and fixing the position of the member is provided, and a light-shielding member that covers the gap between the front group lens and the rear group lens in the circumferential direction is provided at the opening of the lens block. And

  According to the sixteenth aspect of the invention, in the image reading unit of the fifteenth aspect, the light shielding member is divided into two along the optical axis direction of the front group lens unit and the rear group lens unit. An optical unit characterized by. It is characterized by having.

  According to the seventeenth aspect of the present invention, in the optical unit according to the fifteenth aspect, the shading member extends a body portion of the front group lens unit toward the rear group lens unit, and the body of the rear group lens unit. It is characterized by covering at least the end portion on the gap side of the portion from the outside.

  According to the eighteenth aspect of the present invention, in the image reading unit of the seventeenth aspect, the light shielding member is cylindrical.

  According to the nineteenth aspect of the invention, in the image reading unit of the fifteenth aspect, the light shielding member is provided so as to shield light between the rear group lens unit and the photoelectric conversion member.

  According to Claim 20, in the image reading unit according to Claim 19, the light shielding member is a cover.

  According to the twenty-first aspect, in the image reading unit according to any one of the fifteenth to twentieth aspects, the front group lens unit and the rear group lens unit can be slid in the optical axis direction with respect to the lens block, respectively. It is mounted.

  An image forming apparatus according to claim 22 is characterized by using the image reading unit according to any one of claims 15 to 21.

  The present invention can reduce noise light in an optical unit having a basic configuration composed of two lens units. Accordingly, in an image reading unit, an image reading apparatus, and an image forming apparatus using these, an image of a read image can be reduced. It is possible to obtain a good image without deterioration, S / N reduction, MTF deterioration, and color reproducibility deterioration.

  The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.

  FIG. 2 is a cross-sectional view showing an outline of an example of an image forming apparatus using an image reading apparatus including an optical unit according to the present invention. In the figure, reference numeral 100 denotes an image forming unit, 200 denotes a paper feeding unit, 300 denotes an image reading unit comprising the image reading apparatus of the present invention, and 400 denotes a document feeding unit.

  The document feeder 400 feeds the document directly or directly above the image reading unit 300 either automatically or manually. The image reading unit 300 drives a first carriage 5 and a twenty-second carriage 6 (described later) in a sub-scanning direction at a predetermined speed, and takes a document image into a sensor (not shown) by the lens unit 7. The image forming unit 100 forms an image by color-coding a plurality of photoconductors based on the color-separated information of the read image, and superimposes and transfers the image onto a transfer sheet sent from the paper feeding unit 200. Make a full color hard copy. Although the image forming apparatus has been described as an example in FIG. 2, for example, the optical unit and the image reading apparatus according to the present invention can be used in a facsimile machine or the like including the document feeding unit 400 and the image reading unit 300 as basic configurations.

  FIG. 3 is a perspective view showing main components of the image reading apparatus according to the present invention. In the figure, reference numeral 1 is a main body frame, 2 is a drive shaft, 3 is a drive wire, 4 is a wire drive pulley, 5 is a first carriage, 6 is a second carriage, and 7 is a lens unit.

  The image reading apparatus includes a first rail (not shown) and a second rail 8 (not shown) in a main body frame 1 that is a housing of the apparatus. A first carriage 5 is provided on the first rail. The second carriage 6 is slidably disposed on the two rails 8. A wire drive pulley 4 is attached to a drive shaft 2 connected to a motor (not shown), and a drive wire 3 is wound around the drive shaft 2. Although two drive wires 3 for the first carriage 5 and the second carriage 6 are used, only the drive wire 3 for the second carriage 6 is shown in FIG. The drive wire 3 is configured to pass through a carriage pulley attached to the second carriage 6 and an idler pulley provided near the end of the main body frame 1, but the illustration is omitted. Although not shown, the drive motor is arranged on the back side in FIG.

  The first carriage 5 is provided with a tubular lamp 5 a as a light source, and is disposed between the wire drive pulley 4 and the second carriage 6. When the first carriage 5 is pulled by the drive wire and moves at a predetermined speed v, the document placed on the plane of the contact glass that forms an image reading area (not shown) immediately above the tubular lamp 5a is sub-scanned. The reflected light beam from the original is also reflected by a first mirror (not shown) in a predetermined direction, that is, toward the second carriage 6. The reflected light beam is folded back by the second mirror of the second carriage 6 and a third mirror (not shown) and enters the lens unit 7. The reflected light beam is condensed and imaged on an image reading sensor (not shown) placed on the focal plane by the imaging lens included in the lens unit 7, whereby the reading sensor has a linear portion on the original along the tubular lamp 5a. The main scan is performed.

  The second carriage 6 is in the same direction as the first carriage 5 at half the speed of the first carriage 5, that is, at a speed of v / 2, in order to cancel out the overlapping of the optical path due to the folding of the light flux by the two mirrors. Move to. Due to this movement speed relationship, even if the carriage moves, the optical path length of the light beam from the document surface to the lens unit does not change.

  Since the traveling range of the second carriage 6 is half that of the first carriage 5, almost half of the second rail 8 on the side close to the wire driving pulley 4 is not used for traveling of the second carriage 6. However, if the unused portion is cut off, the parallelism of the second rail 8 is adversely affected, so that the shape remains. Instead, the drive shaft 2 of the wire drive pulley 4 is disposed in the region, and the second Arrangement can be made so as to partially overlap the rail surface of the rail 8. In practice, the overlapping portion changes the shape of the rail so that the rotation of the drive shaft 2 is not hindered.

  Conventionally, the upper end of the drive shaft 2 is disposed so as to be lower than the rail surfaces of the first and second rails. However, as in this embodiment, the upper end of the drive shaft 2 is at least the rail surface. By arranging so as not to be lower, the wire driving pulley 4 can be brought closer to the document surface side than the conventional position, which can contribute to the downsizing of the apparatus.

  The lens unit 7 is arranged so that the first carriage 5 can travel on the lens unit 7. However, the lens unit 7 must be disposed outside the traveling region of the second carriage 6 in order to receive a reflected light beam from the document. Conventionally, since the position in the height direction of the drive shaft 2 is below the rail surface of the second rail 8, the distance between the wire drive pulley 4 and the idler pulley (not shown) in the height direction is large, and the relationship of the wire winding In the present embodiment, the position of the drive shaft 2 can be increased to a position where it interferes with the upper surface of the second rail 8, so that the height direction can be reduced. The wire drive pulley 4 can be brought closer to the idler pulley.

  FIG. 4 is a schematic diagram for explaining the relationship between the drive wire 3 for the second carriage 6 and the pulley. FIG. 2A is a side view, FIG. 2B is a view showing the connection state of the drive wires 3 as viewed from above, and FIG. 2A shows the drive wires 3 positioned on the back side of the apparatus main body. FIG. 4B shows the drive wire 3 positioned on the near side of the apparatus main body shown in FIG. In this figure, reference numeral 9 is a tension spring, 10 is a carriage pulley, 11 and 12 are idler pulleys, and 3a to 3f are portions of the drive wire 3 that are stretched between the fixed portion and the pulleys or between the pulleys.

  The drive wire 3 has two systems that are wound around the wire drive pulley 4 and extend leftward and rightward. A portion 3a of the drive wire extending in the left direction is turned back to a portion 3b by an idler pulley 11 having a shaft fixed to the frame 1, reaches the outer carriage pulley 10b, and is turned back again to become a portion 3c. The end is fixed. The portion 3d of the drive wire 3 extending in the right direction is folded back by an idler pulley 12 whose shaft is fixed to the frame 1 to become a portion 3e to reach the inner carriage pulley 10a, where it is folded back again to become a portion 3f. It is fixed to the apparatus main body via a tension spring 9 for application. The rotation of the wire driving pulley 4 causes the carriage pulley 10 to move left and right along the second rail 8 together with the second carriage 6, so that the wire portion 3b and the portion 3c that are directly involved in the carriage 10 are in relation to the second rail. It must be set to be parallel. This is because the constant velocity associated with the movement of the second carriage cannot be guaranteed. For the same reason, the part 3e and the part 3f are also set to be parallel to the second rail. On the other hand, since there is no movement of the position of the pulley between the wire drive pulley 4 and the shaft-fixed idler pulley 11 (or 12), the portions 3a and 3d are not required to be parallel to the second rail. The inner carriage pulley 10a and the outer carriage pulley 10b are concentric and integrally formed double groove pulleys.

  The shafts of the two idler pulleys 11 and 12 are attached to be inclined, and the shaft of the carriage pulley 10 is also attached to be inclined. However, the inclination directions of the idler pulley and the carriage pulley are opposite to each other. That is, assuming that the drive shaft 2 of the wire drive pulley 4 is set to be horizontal, the idler pulleys 11 and 12 are inclined so that the shaft is lowered toward the inside of the main body, whereas the shaft of the carriage pulley 10 is set. Is inclined so that the outside of the main body is lower.

  In the portion 3 a of the drive wire 3, the winding start position slightly moves in the axial direction as the wire drive pulley 4 rotates. When the portion 3a is closest to the second carriage, the wire and the carriage come into contact with each other in the conventional method. Therefore, the wire and the carriage are prevented from coming into contact with each other by inclining the idler pulley 11 and separating the portion 3a from the carriage pulley 10.

  FIG. 5 is a view of the positional relationship between the pulleys on the back side of the apparatus as viewed from the direction of extending the drive wire. In the figure, reference numeral 13 denotes a drive motor, 14 denotes a drive belt pulley, 15 denotes a drive belt, and A and B denote arrows indicating the side on which the pulley shaft is lowered from the horizontal.

  The drive belt pulley 14 is fixed to the output shaft 13a of the drive motor 13 set horizontally. The drive belt 15 is stretched between the drive belt pulley 14 and the driven belt pulley 16. The driven belt pulley 16 is coaxially fixed to the drive shaft 2 together with the wire drive pulley 4. As the drive motor 13 rotates in an arbitrary direction, the wire drive pulley 4 rotates in a corresponding direction, and the drive wire 3 moves in a direction perpendicular to the paper surface in FIG.

  In FIG. 5, the right direction is the center side of the apparatus. The drive shaft 2 of the wire drive pulley 4 is set horizontally, but the idler pulley 11 is arranged so as to become lower toward the inside of the apparatus as indicated by an arrow A. On the other hand, the carriage pulley 10 is arranged so as to become lower toward the outside of the apparatus as indicated by an arrow B. The center positions of the pulleys are arranged in the order of the wire drive pulley 4, idler pulley 11, and carriage pulley 10 from the outside of the apparatus to the inside along the direction of the drive shaft 2.

  Further, the upper end of the wire drive pulley 4 is located above the lower end of the first idler pulley 11. This is a condition for making the entire apparatus low. However, the upper end of the wire drive pulley 4 is located below the upper end of the first idler pulley. This is a condition for preventing the drive wire 3 and the wire drive pulley 4 from interfering with each other. These relationships are the same for the second idler pulley 12.

  When the drive wire 3 is passed from the wire drive pulley 4 to the idler pulley 11, the drive wire 3 is positioned substantially on the tangent line of the wire drive pulley 4, and the winding start point of the idler pulley is present on the extension. Actually, the winding start position of the drive wire 3 with respect to the wire drive pulley 4 (corresponding to a contact when the wire is regarded as tangent) moves slightly in the axial direction. To do.

  When the drive wire 3 is stretched between the idler pulley 11 and the carriage pulley 10, the drive wire 3 is arranged so as to be positioned on the tangent line of both pulleys. In other words, the drive wire 3 is positioned to coincide with the common outer tangent line of the carriage pulley 10 and the idler pulley 11. Therefore, the winding start position for both pulleys overlaps the same point in FIG. The wire drive pulley 4 and the drive wire 3 in other parts of the carriage pulley 10 are omitted. The same can be said for the idler pulley 12.

  By adopting such a configuration, there is little overlapping of the wires when viewed in the vertical direction, so that the wire winding operation is simplified. Further, according to this configuration, a stable driving force can be transmitted without applying an excessive force to the driving wire 3. Furthermore, since the pulley is inclined, the height of the image reading apparatus can be reduced.

  FIG. 6 is a cross-sectional view showing a basic structural example of an optical unit according to the present invention and an image reading unit or an image reading apparatus using the optical unit. FIG. 6 has a main configuration corresponding to the conventional FIG. 1 (B), and the reference numerals in the figure are associated with each other. Also, elements not shown in FIG. 6 are described with the same reference numerals as those in FIG.

  Also in this example, the lens 21 is composed of two lens units, a front group lens 23 and a rear group lens 24, and the CCD 22 is positioned behind the rear group lens 24. The rear group lens 24 and the CCD 22 are assembled and adjusted, and their positions are adjusted and determined. Thereafter, the lens block 25 is bonded and fixed via a holding member 26. As shown in FIG. 1, the front lens group 23 and the rear lens group 24 are installed using the opening 29 of the lens block 25.

  As described above, according to the research of the present inventor, when a gap 28 is formed between the front group lens 23 and the rear group lens 24 in the assembled state, light enters from the gap 28 and In this example, in order to block noise light or flare light, the illustrated cylindrical light shielding member 30 is disposed so as to straddle both the front group lens 23 and the rear group lens 24. Yes. The front group lens 23, the rear group lens 24, and the light shielding member 30 are configured to have a slight gap that can be slid so as not to hinder the position adjustment described above. The light shielding member 30 prevents external light from entering from the gap 28 between the front group lens 23 and the rear group lens 24, and can prevent the above-described problems from occurring.

  FIG. 7 is a sectional view showing a second embodiment of the optical unit according to the present invention and an image reading unit or an image reading apparatus using the optical unit. In the embodiment of this figure, the light shielding member 30 is divided into an upper light shielding member 30a and a lower light shielding member 30b by dividing the light shielding member 30 into upper and lower parts. 29 can be easily attached. In the figure, a hole 31 is formed in the flange of the upper light-shielding member 30a, a pin 32 is provided in the flange of the lower light-shielding member 30b, and both are integrated so that the pin 32 fits into the hole 31 during assembly. Of course, other configurations are possible. Moreover, although the example shown in the drawing is only an example of upper and lower two divisions, it may be divided into a larger number, and the form of division may be left / right or upper / lower, other than left / right, and is not limited to the example shown.

  FIG. 8 is a sectional view showing an optical unit according to the present invention and an image reading unit or an image reading apparatus using the same according to a third embodiment. In this embodiment, a separate light shielding member is not used, and the rear side of the front group lens 23 is formed in a cylindrical shape to form a light shielding portion 23a as shown in the drawing, while sliding with the rear group lens 24 at the adjustment position. It is configured to engage. With this configuration, it is possible to save assembling work and to reduce the part cost. The front side of the rear lens group 24 may be extended in a cylindrical shape to form a light shielding part. However, since the front group lens 23 generally has a larger cylindrical diameter, the light of the light shielding part is as shown in the figure. It can be said that it is desirable to configure the outlet side to be lower than the inlet side.

  FIG. 9 is a perspective view (A) and a cross-sectional view (B) showing a fourth embodiment of an optical unit according to the present invention and an image reading unit or an image reading apparatus using the optical unit. In this embodiment, as shown in the drawing, not only the gap 28 between the front group lens 23 and the rear group lens 24 but also a box shape or an upper cover shape so as to cover the space between the rear group lens 24 and the CCD 22. By adopting a configuration including the light blocking member 40, stray light incident on the CCD 22 can also be blocked.

  The light shielding member 40 of the present embodiment does not cover the gap 28 on the lower side of the lens block 25. However, for example, a separate light shielding member may be prepared to cover the lower side of the lens block 25. . The separate light shielding member may be of a type that covers only the lower gap 28 of the lens block 25 and the vicinity thereof, such as the lower light shielding member 30b shown in FIG.

  In the embodiments described above, only a cylindrical shape, a box shape, or a cover shape is shown, but other shapes may be used, and the shape and structure are not limited to those shown in the drawings.

Sectional view of a conventional example of an image reading apparatus or an image reading unit used in an image forming apparatus Sectional drawing which shows the outline | summary of an example of the image forming apparatus using the image reading apparatus containing the optical unit which concerns on this invention 1 is a perspective view showing main components of an image reading apparatus according to the present invention. Schematic diagram for explaining the relationship between the drive wire for the second carriage and the pulley View of the positional relationship of each pulley on the back of the device as seen from the direction of the drive wire extension Sectional drawing which shows the fundamental structural Example of the optical unit which concerns on this invention, and an image reading unit or image reading apparatus using the same Sectional drawing which shows 2nd Example of the optical unit which concerns on this invention, and an image reading unit or image reading apparatus using the same. Sectional drawing which shows 3rd Example of the optical unit which concerns on this invention, and an image reading unit or image reading apparatus using the same. A perspective view (A) and a sectional view (B) showing a fourth embodiment of an optical unit according to the present invention and an image reading unit or an image reading apparatus using the optical unit.

Explanation of symbols

7 Lens unit 21 Lens 22 Photoelectric conversion element (CCD)
23 Front group lens 23a Light shielding part 24 Rear group lens 25 Lens block 26 Holding member 27 CCD substrate 29 Lens block opening 30 Light shielding member 30a Upper light shielding member 30b Lower light shielding member 31 Hole 32 Pin 40 Light shielding member

Claims (22)

A first lens unit; a second lens unit; a lens block for determining the positions of the first and second lens units; and a light-shielding member that shields light between the first and second lens units. An optical unit comprising: 2. The optical unit according to claim 1, further comprising photoelectric conversion means for photoelectrically converting light that has passed through the first lens unit and the second lens unit. 3. The optical unit according to claim 2, further comprising a substrate on which a circuit for controlling input / output signals of the photoelectric conversion means is mounted. 4. The optical unit according to claim 1, wherein the light shielding member covers a gap between the first and second lens units from the outside. 5. The optical unit according to claim 4, wherein the light blocking member is divided into two or more along the optical axis direction of the first and second lens units. 6. The optical unit according to claim 4, wherein the light shielding member is cylindrical. 4. The optical unit according to claim 1, wherein the light-shielding member extends either one of the first lens unit and the second lens unit to the other side, and the lens unit of the other lens unit. An optical unit characterized in that it covers at least the end of the gap on the gap side from the outside. 8. The optical unit according to claim 7, wherein the light shielding member is cylindrical. 5. The optical unit according to claim 4, wherein the light shielding member is provided so as to shield light between the second lens unit and the photoelectric conversion means. The optical unit according to claim 9, wherein the light shielding member is a cover. 11. The optical unit according to claim 1, wherein the first lens unit and the second lens unit are mounted so as to be slidable in the optical axis direction with respect to the lens block. An image reading apparatus comprising the optical unit according to claim 1. An image forming apparatus comprising the optical unit according to claim 1. An image forming apparatus using the image reading apparatus according to claim 13. An image including an optical element having a transmission surface through which a light beam passes, a photoelectric conversion member that photoelectrically converts light that has passed through the transmission surface, and a substrate on which a circuit that controls input / output signals of the photoelectric conversion member is mounted In the reading unit, the optical element includes two lens units, a front group lens unit and a rear group lens unit, and a lens for adjusting and fixing the position of each lens unit and the position of the photoelectric conversion member. An image reading unit comprising a block, and a light shielding member that covers a gap between the front lens group and the rear lens group in a circumferential direction at an opening of the lens block. 16. The optical unit according to claim 15, wherein the light shielding member is divided into two along the optical axis direction of the front group lens unit and the rear group lens unit. An image reading unit comprising: 16. The optical unit according to claim 15, wherein the light blocking member extends at least the gap side end of the body portion of the rear group lens unit by extending the body portion of the front group lens unit toward the rear group lens unit. An image reading unit that covers the outside from the outside. 18. The image reading unit according to claim 17, wherein the light shielding member is cylindrical. 16. The image reading unit according to claim 15, wherein the light shielding member is provided so as to shield light even between the rear lens group unit and the photoelectric conversion member. 20. The image reading unit according to claim 19, wherein the light shielding member is a cover. 21. The image reading unit according to claim 15, wherein the front group lens unit and the rear group lens unit are mounted to be slidable in the optical axis direction with respect to the lens block. unit. An image forming apparatus comprising the image reading unit according to claim 15.