CN219349242U - Cover glass and image forming apparatus - Google Patents

Abstract

A protective glass (L1) is provided on a housing (12) of an image forming apparatus (1) so as to cover the inside of the housing (12), and includes a first surface (S1) on an object side and a second surface (S2) on an image side, at least one of the first surface (S1) and the second surface (S2) being convex or concave so as to absorb light from the object side to the image side.

Description

Cover glass and image forming apparatus

Technical Field

The present utility model relates to a cover glass and an image forming apparatus, and more particularly, to a cover glass and an image forming apparatus which are small and capable of achieving good optical performance.

Background

Conventionally, an optical system composed of a front group optical system having a negative refractive index and a rear group optical system having a positive refractive index in order from the object side is called an imaging optical system for imaging devices such as an in-vehicle camera, a monitoring camera, a camera, and an electronic still camera.

In recent years, portable imaging devices such as mobile phones and digital cameras have been widely used. With recent miniaturization of imaging apparatuses, miniaturization of imaging lenses mounted on the imaging apparatuses is also required.

Conventionally, in an imaging apparatus, a cover glass may be provided on an object side of an imaging lens to prevent foreign substances from entering the imaging lens while light is acquired from the object side.

However, in the conventional imaging apparatus, a cover glass is provided on the object side of the imaging lens, and the cover glass cannot be effectively used as an optical system, so that it is difficult to obtain good optical characteristics in a small configuration.

Disclosure of Invention

The present utility model is directed to solving at least one of the above-mentioned technical problems, and therefore, there is a need to provide a cover plate and an image forming apparatus.

According to the present utility model, a cover glass provided on a housing of an image forming apparatus to cover an inside of the housing, the cover glass comprising: a first surface located on an object side; and a second surface at an image side; wherein at least one of the first surface and the second surface is convex or concave to absorb light from the object side to the image side.

In one example, the housing is provided with a through hole, and the cover glass is disposed inside the through hole to fill the through hole.

In one example, the housing is provided with a through hole, and the cover glass is accommodated in the lens barrel and the lens barrel is arranged in the through hole so as to fill the through hole.

In one example, the housing is provided with a through hole, and the cover glass is disposed on a side of the through hole close to the object side in the optical axis direction so as to cover the through hole.

In one example, the housing is provided with a through hole, and the cover glass is disposed on a side of the through hole away from the object side in the optical axis direction so as to cover the through hole.

In one example, the cover glass and at least one lens disposed on the image side with respect to the cover glass have a common optical axis.

In one example, the cover glass has a positive refractive index.

In one example, the cover glass has a negative refractive index.

In one example, the first surface is planar and the second surface is convex toward the image side.

In one example, the first surface is convex toward the object side and the second surface is planar.

In one example, the first surface is convex toward the object side and the second surface is convex toward the image side.

In one example, the first surface is convex toward the object side, the second surface is concave toward the image side, and a central radius of curvature of the second surface is greater than a central radius of curvature of the first surface.

In one example, the first surface is concave toward the object side, the second surface is convex toward the image side, and a central radius of curvature of the second surface is smaller than a central radius of curvature of the first surface.

In one example, the first surface is planar and the second surface is concave toward the image side.

In one example, the first surface is concave toward the object side and the second surface is planar.

In one example, the first surface is a concave surface toward the object side and the second surface is a concave surface toward the image side.

In one example, the first surface is convex toward the object side, the second surface is concave toward the image side, and a radius of curvature of the second surface is smaller than a center radius of curvature of the first surface.

In one example, the first surface is a concave surface toward the object side, the second surface is a convex surface toward the image side, and a central radius of curvature of the second surface is greater than a central radius of curvature of the first surface.

In one example, the cover glass may be movable in the optical axis direction.

According to the present utility model, an image forming apparatus includes a housing, a cover glass provided on the housing, and at least one other lens provided in the housing with respect to an image side of the cover glass.

Drawings

These and/or other aspects and advantages of embodiments of the present disclosure will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings, wherein:

fig. 1 is a configuration diagram of a cover glass according to a first example of the present utility model.

Fig. 2 is a schematic cross-sectional view of an image forming apparatus equipped with the cover glass of fig. 1.

Fig. 3 is a schematic cross-sectional view of an image forming apparatus equipped with a conventional cover glass.

Fig. 4 is a front view of a specific example of an image forming apparatus including the cover glass of fig. 1.

Fig. 5 is a rear view of fig. 4.

Fig. 6 is a configuration diagram of a cover glass according to a second example of the present utility model.

Fig. 7 is a configuration diagram of a cover glass according to a third example of the present utility model.

Fig. 8 is a configuration diagram of a cover glass according to a fourth example of the present utility model.

Fig. 9 is a view showing a modification of the cover glass.

Fig. 10 is a view showing a modification of the cover glass.

Fig. 11 is a view showing a modification of the cover glass.

Fig. 12 is a view showing a modification of the cover glass.

Fig. 13 is a view showing a modification of the cover glass.

Fig. 14 is a view showing a modification of the cover glass.

Fig. 15 is a view showing a modification of the cover glass.

Fig. 16 is a view showing a modification of the cover glass.

Fig. 17 is a view showing a modification of the cover glass.

Detailed Description

Embodiments of the present utility model will be described in detail, and examples of the embodiments are illustrated in the accompanying drawings. Throughout the description, identical or similar elements and elements having identical or similar functions are denoted by similar reference numerals. The embodiments described herein with reference to the drawings are illustrative of the utility model and are not to be construed as limiting the utility model.

[ summary of the utility model ]

First, an outline of the present utility model will be described. The configuration of the cover glass to which the present utility model is applied is shown in fig. 1, 6, 7 and 8. In the figure, a dotted line-dotted line indicates the optical axis of the camera module.

The cover glass L1 is provided on the housing 12 of the image forming apparatus 1 to cover the inside of the housing 12. The imaging device 1 is for example a compact digital device such as a mobile phone, a wearable camera and a surveillance camera. The image forming apparatus 1 includes the cover glass L1 and the housing 12. More specifically, as shown in fig. 2, the imaging apparatus 1 includes a camera module 11 and the housing 12 accommodating the camera module 11. As shown in fig. 2 and 3, the camera module 11 includes an imaging lens 21, an optical filter 22, and an image sensor 23. The imaging lens 21 includes the cover glass L1 and at least one other lens L2, the other lens L2 being disposed on the image side S with respect to the cover glass L1 located in the housing 12. The protective glass L1 serves as a lens protective filter with respect to the other lens L2.

The cover glass L1 has a first surface S1 located on the object side and a second surface S2 located on the image side S. At least one of the first surface S1 and the second surface S2 is convex or concave in order to absorb light from the object side to the image side S. The convex and concave surfaces may be spherical or aspherical.

The cover glass L1 and the other lens L2 have a common optical axis. For example, the cover glass L1 is a lens whose position is fixed in the housing 12. The cover glass L1 can be moved in the optical axis direction inside the housing 12 by an actuator. At least some of the other lenses L2 may be moved in the optical axis direction in the housing 12 by an actuator. During the focusing operation, a lens that moves in the optical axis direction may be used to adjust the focus of the imaging lens 21 to the subject.

The image sensor 23 is, for example, a solid-state image sensor such as CMOS (complementary metal oxide semiconductor) or CCD (charge coupled device). The image sensor 23 has the image side S as an imaging plane of the imaging lens 21. The image sensor 23 receives light incident from the subject (object side) via the imaging lens 21 and the optical filter 22, photoelectrically converts the light, and outputs image data obtained by photoelectrically converting the light to the next stage.

In order to obtain the imaging apparatus 1 having an imaging lens of a small size and good optical performance, it is necessary to appropriately correct various aberrations by utilizing a limited space in the optical axis direction of the imaging apparatus 1.

Therefore, in the image forming apparatus 1, the cover glass L1, one of which is convex or concave, of the first surface S1 and the second surface S2 is provided on the housing 12 so as to cover the inside of the housing 12.

With this configuration, the imaging apparatus 1 can make the area a in the optical axis direction, which effectively serves as an optical system (see fig. 2), larger than that of a conventional imaging apparatus including a cover glass G (see fig. 3) arranged on the object side of an imaging lens L2. Since the area a of the imaging apparatus 1 is larger than that of a conventional imaging apparatus, various aberrations can be advantageously corrected by appropriately adjusting the number of lenses and refractive index in the area a of the imaging apparatus 1. Therefore, even if the arrangement is small, good optical characteristics can be obtained.

Further, in view of lens molding, it is preferable to form an aspherical lens constituting the imaging lens 21, particularly an aspherical lens having an aspherical shape with an inflection point, from a plastic material (glass material). Further, among lenses constituting the imaging lens 21, a lens having a size equal to or smaller than a specific size may be a lens formed of a plastic material, and a lens having a size larger than a specific size may be a lens formed of a glass material. This is because it is difficult to form an aspherical lens or a relatively small lens using a glass material instead of plastic.

First example

Next, specific examples to which the present utility model is applied will be described. First, a first example of the protective glass L1 shown in fig. 1 will be described in detail.

In the first example, a through hole 121 is opened on the case 12, and the cover glass L1 is disposed inside the through hole 121 to fill the through hole 121.

In the first example, the cover glass L1 has a negative refractive index. More specifically, the first surface S1 is a plane orthogonal to the optical axis direction, and the second surface S2 is a concave surface facing the image side S.

According to the first example, the protective glass L1 inside the through hole 121 opened on the housing 12 can be made larger in area in the optical axis direction effective as an optical system than that of the conventional imaging apparatus having the protective glass G. Therefore, even if the arrangement is small, good optical characteristics can be obtained. Further, since the cover glass L1 is arranged inside the through hole 121 so as not to protrude from the housing 12 toward the object side, the size, i.e., thickness, of the imaging apparatus 1 in the optical axis direction can be suppressed.

Further, in the conventional configuration having the cover glass G, there may occur "vignetting" in which light from an object incident on the imaging lens peripheral side at a large incident angle is blocked by the cover glass G or the lens barrel. Therefore, in the conventional configuration, it is difficult to achieve a sufficiently wide angle. In contrast, according to the configuration of the first example, a sufficiently wide-angle lens that sufficiently suppresses "vignetting" can be realized by including the cover lens L1 having a negative refractive index instead of the conventional cover glass.

The cover glass L1 of the first example may be applied to, for example, the mobile phone 10 shown in fig. 4 and 5. The mobile telephone 10 includes a generally rectangular housing 12. On the front side of the housing 12, a display unit 101 and a front camera unit 102 (see fig. 4) as an example of one of the camera modules 11 are provided. On the back surface of the housing 12, a main camera unit 103 and a camera flash 104 (see fig. 5) are provided as an example of the camera module 11.

The display unit 101 is, for example, a touch panel that realizes various operations by detecting a contact state with the surface of the display unit 101. Accordingly, the display unit 101 has a display function of displaying various information and an input function of allowing the user to perform various input operations. The display unit 101 displays various data such as an operation state and an image photographed by the front camera unit 102 or the main camera unit 103.

For example, as shown in fig. 5, the cover glass L1 may be used as a lens of the main camera unit 103. The cover glass L1 may also be used as a lens of the front camera unit 102.

The front camera unit 102 may be disposed at the rear of the display unit 101 so as not to be exposed from the front of the housing 12.

The main camera unit 103 may include a plurality of camera modules 11. In this case, the plurality of camera modules 11 may be arranged side by side along the rear surface of the housing 12, and one cover glass L1 may be shared between the plurality of camera modules 11. In the case where one cover glass L1 is shared among the plurality of camera modules 11, the surface of the cover glass L1 may be formed in a shape matching each of the plurality of camera modules 11. Alternatively, one cover glass L1 may be provided for each camera module 11.

Second example

Next, a second example of the cover glass L1 shown in fig. 6 will be described in detail.

In the second example, a through hole 121 is opened on the housing 12, and the cover glass L1 is arranged inside the through hole 121 together with the lens barrel 13 in a state of being accommodated in the lens barrel 13 to fill the through hole 121. In addition to the cover glass L1, another lens L2 may be accommodated in the lens barrel 13.

Further, in the second example, the cover glass L1 has a negative refractive index, the first surface S1 is a plane, and the second surface S2 is a concave surface toward the image side S.

Similar to the first example, the cover glass L1 of the second example may be applied to a main camera unit 103 or a front camera unit 102 in the mobile phone 10.

According to the second example, the cover glass L1 is arranged inside the through hole 121 together with the lens barrel 13 in a state of being accommodated in the lens barrel 13, the through hole 121 is provided on the housing 12, and it is possible to make the area of the area effectively used as an optical system in the optical axis direction larger than that of the area effectively used as an optical system of a conventional imaging apparatus having the cover glass G. Therefore, even in the case of a small configuration, good optical characteristics can be obtained. Further, by accommodating the other lens L2 together with the cover glass L1 in the lens barrel 13, it is possible to avoid aligning the accommodated lenses L1 and L2. Further, if the lens barrel 13 is formed of a light shielding material, deterioration of optical characteristics due to incidence of light from the side surface of the protective glass L1 can be prevented.

Third example

Next, a third example of the protective glass L1 shown in fig. 7 will be described in detail.

In the third example, a through hole 121 is opened in the case 12, and the cover glass L1 is disposed on a side of the through hole 121 close to the object side in the optical axis direction so as to cover the through hole 121. As in the second example, the cover glass L1 may be encapsulated in the lens barrel 13.

Further, in the third example, the cover glass L1 has a negative refractive index, the first surface S1 is a plane, and the second surface S2 has a concave surface toward the image side S.

Similar to the first example, the cover glass L1 of the third example may also be applied to the main camera unit 103 or the front camera unit 102 in the mobile phone 10.

According to the third example, the protective glass L1 disposed on the object side to cover the through hole 121 with respect to the through hole 121 opened on the housing 12 can make the area effective as an optical system larger in the optical axis direction than that of the area effective as an optical system of the conventional imaging apparatus having the protective glass G. Therefore, even in the case of a small configuration, good optical characteristics can be obtained.

Fourth example

Next, a fourth example of the protective glass L1 shown in fig. 8 will be described in detail.

In the fourth example, the through hole is opened on the case 12, and the cover glass L1 is arranged on the image side S with respect to the through hole 121 so as to cover the through hole 121. As in the second example, the cover glass L1 may be packaged in the lens barrel 13.

In the fourth example, the protective glass L1 has a negative refractive index, the first surface S1 is a plane, and the second surface S2 is a concave surface toward the image side S.

The cover glass L1 of the fourth example can also be applied to the main camera unit 103 or the front camera unit 102 in the mobile phone 10, similarly to the first example.

According to the fourth example, the area of the region that can be used as an optical system, which is arranged on the image side S to cover the through hole 121, with respect to the through hole 121 opened on the housing 12 is larger in the optical axis direction than that of a conventional imaging apparatus having a cover glass G. Therefore, even in the case of a small configuration, good optical characteristics can be obtained. In addition, an optical member such as an optical filter may be placed inside the through hole 121 or on the object side of the through hole 121 to adjust optical characteristics.

Modification

Next, a modification of the surface shape of the cover glass L1 will be described. The cover glass L1 in which the first surface S1 is a plane and the second surface S2 is a concave surface toward the image side S is described. However, the surface shapes of the first surface S1 and the second surface S2 are not limited thereto.

For example, as shown in fig. 9, the first surface S1 may be a concave surface facing the object side, and the second surface S2 may be a plane.

Further, as shown in fig. 10, the first surface S1 may be a convex surface toward the object side, and the second surface S2 may be a concave surface toward the image side S. The second surface S2 has a central radius of curvature smaller than the central radius of curvature of the first surface S1.

As shown in fig. 11, the first surface S1 may be a concave surface toward the object side, and the second surface S2 may be a convex surface toward the image side S. The second surface S2 has a central radius of curvature that is greater than the central radius of curvature of the first surface S1.

Further, as shown in fig. 12, the first surface S1 may be a concave surface toward the object side, and the second surface S2 may be a concave surface toward the image side S.

Although the cover glass L1 having the above-described surface shape has a negative refractive index, the present utility model can also be applied to a cover glass L1 having a positive refractive index.

In this case, as shown in fig. 13, the first surface S1 may be a plane, and the second surface S2 may be a convex surface toward the image side S.

Further, as shown in fig. 14, the first surface S1 may be a convex surface toward the object side, and the second surface S2 may be a plane.

As shown in fig. 15, the first surface S1 may be a convex surface toward the object side, and the second surface S2 may be a concave surface toward the image side S. The second surface S2 has a central radius of curvature that is greater than the central radius of curvature of the first surface S1.

As shown in fig. 16, the first surface S1 may be a concave surface toward the object side, and the second surface S2 may be a convex surface toward the image side S. The second surface S2 has a central radius of curvature smaller than the central radius of curvature of the first surface S1.

Further, as shown in fig. 17, the first surface S1 may be a convex surface toward the object side, and the second surface S2 may be a convex surface toward the image side S.

In describing embodiments of the present utility model, terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise" and "counter-clockwise" should be construed to refer to directions or locations as described or as shown in the drawings in the discussion. These relative terms are only used to simplify the description of the present utility model and do not denote or imply that the referenced devices or elements must have a particular orientation or must be constructed or operated in a particular orientation. Accordingly, these terms are not intended to limit the present utility model.

Furthermore, terms such as "first" and "second" are used herein for descriptive purposes and are not intended to represent or imply relative importance or importance, or to imply the number of technical features indicated. Thus, features defined as "first" and "second" may include one or more of the features. In the description of the present utility model, "plurality" means "two or more" unless specified otherwise.

In the description of embodiments of the utility model, terms such as "mounted," "connected," "coupled," and the like are used broadly and may be, for example, fixedly connected, detachably connected, or integrally connected, unless otherwise specified or limited; or may be a mechanical or electrical connection; or may be directly or indirectly connected through intermediate structures; internal communication of two elements as would be understood by one skilled in the art in the specific case is also possible.

In embodiments of the utility model, unless specified or limited otherwise, structures in which a first feature is "above" or "below" a second feature may include embodiments in which the first feature is in direct contact with the second feature, and may also include embodiments in which the first feature and the second feature are not in direct contact with each other, but are in contact by forming additional features therebetween. Further, a first feature "above," "over" and "on" a second feature may be that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

Various embodiments and examples are provided in the above description to implement different structures of the present utility model. In order to simplify the present disclosure, certain elements and arrangements are described above. However, these elements and arrangements are merely examples and are not intended to limit the present utility model. Furthermore, reference numbers and/or reference letters may be repeated in different examples of the utility model. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations. In addition, the present utility model provides examples of different processes and materials. However, those skilled in the art will appreciate that other processes and/or materials may also be applied.

Reference in the specification to "an embodiment," "some embodiments," "example embodiments," "examples," "particular examples," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the utility model. Thus, the appearances of the above-described phrases in this specification are not necessarily referring to the same embodiment or example of the utility model. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Any process or method described in the flow diagrams or otherwise described herein may be understood as comprising one or more modules, segments, or portions of code of executable instructions for implementing specific logical functions or steps in the process, and the scope of the preferred embodiments of the present utility model includes other implementations in which functions may be implemented in sequences other than those shown or discussed, including substantially the same sequence or the opposite sequence.

The logic and/or steps described elsewhere herein or shown in a flowchart, e.g., a particular sequence of executable instructions for implementing the logic function, may be embodied in any computer readable medium for use by an instruction execution system, apparatus or device (e.g., a computer-based system, system that includes a processor or other system that can obtain instructions from the instruction execution system, apparatus or device that executes instructions), or apparatus or device that is used in combination with an instruction execution system, apparatus or device. For the purposes of this description, a "computer-readable medium" can be any means that can be used in any suitable manner to contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples of the computer-readable medium include, but are not limited to: an electronic connection (electronic device) having one or more wires, a portable computer housing (magnetic device), random Access Memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), fiber optic equipment, and portable compact disc read-only memory (CDROM). Further, the computer-readable medium may even be paper or other suitable medium on which the program can be printed, since, for example, the paper or other suitable medium may be optically scanned and then edited, decrypted or processed by other suitable methods when it is necessary to obtain the program electronically, and the program may then be stored in a computer memory.

It is to be understood that each portion of the present utility model may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the steps or methods may be implemented by software or firmware stored in a memory and executed by an appropriate instruction execution system. For example, if implemented in hardware, also in another embodiment, the steps or methods may be implemented by one or a combination of the following techniques, which are known in the art: discrete logic circuits having logic gates for implementing logic functions for data signals, an application specific integrated circuit having appropriately combined logic gates, programmable Gate Arrays (PGAs), field Programmable Gate Arrays (FPGAs), and the like.

Those skilled in the art will appreciate that all or part of the steps in the above-described exemplary methods of the present utility model may be implemented using program command related hardware. These programs may be stored in a computer readable storage medium and when run on a computer comprise one or more steps of the method embodiments of the present utility model.

Furthermore, each functional unit of the embodiments of the present utility model may be integrated in a processing module, or these units may be physically present alone, or two or more units are integrated in a processing module. The integrated module may be implemented in the form of hardware or software functional modules. When the integrated module is implemented in the form of a software functional module and sold or used as a stand-alone product, the integrated module may be stored in a computer-readable storage medium.

The storage medium may be a read-only memory, a magnetic disk, a CD, or the like.

Although embodiments of the present utility model have been shown and described, it will be understood by those skilled in the art that these embodiments are illustrative and not to be construed as limiting the utility model and that alterations and modifications may be made in the embodiments without departing from the scope of the utility model.

Claims (20)

1. A cover glass provided on a housing of an image forming apparatus to cover an inside of the housing, the cover glass comprising:

a first surface located on an object side; and

a second surface located at an image side; wherein the method comprises the steps of

At least one of the first surface and the second surface is convex or concave to absorb light from the object side to the image side.

2. The cover glass of claim 1, wherein: the shell is provided with a through hole, and the protective glass is arranged in the through hole to fill the through hole.

3. The cover glass of claim 1, wherein: the shell is provided with a through hole, and the protective glass is accommodated in the lens cone and arranged in the through hole so as to fill the through hole.

4. The cover glass of claim 1, wherein: the shell is provided with a through hole, and the protective glass is arranged on one side, close to the object side, of the through hole in the optical axis direction so as to cover the through hole.

5. The cover glass of claim 1, wherein: the shell is provided with a through hole, and the protective glass is arranged on one side, far away from the object side, of the through hole in the optical axis direction so as to cover the through hole.

6. The cover glass of claim 1, wherein: the cover glass and at least one lens disposed on the image side with respect to the cover glass have a common optical axis.

7. The cover glass of claim 1, wherein: the protective glass has a positive refractive index.

8. The cover glass of claim 1, wherein: the protective glass has a negative refractive index.

9. The cover glass of claim 7, wherein: the first surface is a plane, and the second surface is a convex surface facing the image side.

10. The cover glass of claim 7, wherein: the first surface is a convex surface facing the object side, and the second surface is a plane.

11. The cover glass of claim 7, wherein: the first surface is a convex surface facing the object side, and the second surface is a convex surface facing the image side.

12. The cover glass of claim 7, wherein: the first surface is a convex surface facing the object side, the second surface is a concave surface facing the image side, and the center curvature radius of the second surface is larger than that of the first surface.

13. The cover glass of claim 7, wherein: the first surface is a concave surface facing the object side, the second surface is a convex surface facing the image side, and the center curvature radius of the second surface is smaller than that of the first surface.

14. The cover glass of claim 8, wherein: the first surface is a plane, and the second surface is a concave surface facing the image side.

15. The cover glass of claim 8, wherein: the first surface is a concave surface facing the object side, and the second surface is a plane.

16. The cover glass of claim 8, wherein: the first surface is a concave surface facing the object side, and the second surface is a concave surface facing the image side.

17. The cover glass of claim 8, wherein: the first surface is a convex surface facing the object side, the second surface is a concave surface facing the image side, and the curvature radius of the second surface is smaller than the center curvature radius of the first surface.

18. The cover glass of claim 8, wherein: the first surface is a concave surface facing the object side, the second surface is a convex surface facing the image side, and a central curvature radius of the second surface is larger than that of the first surface.

19. The cover glass of any one of claims 1 to 18, wherein: the cover glass is movable in the optical axis direction.

20. An image forming apparatus, comprising:

a housing;

a cover glass according to any one of claims 1 to 19; and

at least one other lens opposite to the protective glass in the shell is arranged on an image side.

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