Hood for projector

Abstract

[Problem] To prevent a light source reflected on a projection lens of a projector from being seen by an audience. [Solution] This hood 200 for a projector can be detachably attached, in the vicinity of a projection lens 122 of a projector 100, to the projector 100, and is configured to block at least the line of sight of the audience to the projection lens 122 from a direction orthogonal to the optical axis L of the projection lens 122 without blocking light projected from the projection lens 122. The hood 200 for a projector comprises: an attachment part 210 detachably attached to a lens unit 120 of the projector 100; and a shielding part 220 which extends in the optical axis direction of the projection lens 122 from the attachment part 210, has an opening through which light passes, and is configured to block the line of sight.

Description

Projector hood

[0001] The present invention relates to a hood for use in a projector for projecting images.

[0002] The applicant of the present application has been providing video works that can give the audience a sense of immersion as if they were inside the video space by projecting video light from a projector onto walls and floors (for example, Patent Documents 1 and 2).

[0003] JP 2019-184776 A JP 2023-128843 A

[0004] However, because the projection lens of a projector has a convex surface, when the projector is viewed from the side, the light source within the projector reflected in the projection lens may be visible to the audience. In particular, when projecting image light onto a wall or floor, the projector is often installed on the ceiling of the exhibition space. However, if the projector is installed at a low position (for example, approximately 4000 mm or less from the floor), the light source reflected in the projection lens of the projector is likely to be visible to the audience. Furthermore, in video works where it is important to give the audience a sense of immersion, if the projector's light source is frequently visible to the audience, the audience may perceive the projector as being more prominent than the projected image, which could detract from the experience of the work.

[0005] Therefore, a main object of the present invention is to prevent the light source reflected in the projection lens of the projector from being visible to the audience.

[0006] The inventor of the present invention has thoroughly investigated means for solving the problems of the prior art, and has discovered that by attaching a hood around the projection lens of a projector to block the audience's line of sight to the projection lens, the audience can be prevented from directly viewing the projection lens. Based on this discovery, the inventor has come to the realization that the problems of the prior art can be solved, and has completed the present invention. Specifically, the present invention has the following configuration.

[0007] The present invention relates to a hood 200 that can be attached to a projector 100. The hood 200 according to the present invention can be detachably attached to the projector 100 around the projection lens 122. That is, the hood 200 can be attached to and detached from the projector 100 even after the projector 100 has been installed in a predetermined position, such as on a ceiling. The hood 200 is configured to block at least the line of sight toward the projection lens 122 from a direction perpendicular to the optical axis L of the projection lens 122 without blocking the light projected from the projection lens 122 of the projector 100. Note that the "line of sight toward the projection lens 122 from a direction perpendicular to the optical axis L of the projection lens 122" refers to the line of sight when the projection lens 122 is viewed from a position at which the optical axis L of the projection lens 122 and the line of sight of an audience or the like intersect perpendicularly at the projection lens 122. In this way, by attaching the hood 200 according to the present invention to the projector 100, the projection lens 122 of the projector 100 becomes less likely to be directly visible to the audience. This makes it less likely for the audience to see the light source inside the projector 100 reflected on the convex surface of the projection lens 122, making the projector 100 less noticeable to the audience. As a result, the sense of immersion in the video work projected using the projector 100 can be enhanced.

[0008] The hood 200 according to the present invention corresponds to the projector 100 equipped with the lens unit 120. The lens unit 120 includes a light guide 121 for changing the direction of light travel and a projection lens 122 provided at the output end of the light guide 121. In this case, the hood 200 according to the present invention includes an attachment portion 210 and a shielding portion 220. The attachment portion 210 is a portion that is detachably attached to the projector 100. The shielding portion 220 extends from the attachment portion 210 in the optical axis direction of the projection lens 122 of the projector 100, has an opening 224 formed therein through which light projected from the projection lens 122 passes, and is configured to block the line of sight of an audience, etc., as described above. The attachment portion 210 includes a main body member 211 and a fitting member 212. The main body member 211 has the shielding portion 220 fixed thereto (main body member 211) and is configured to surround the periphery of the lens unit 120, leaving a portion open. The fitting member 212 has a fitting member that fits into the main body member 211 so as to abut against that portion of the periphery of the lens unit 120 (the portion not surrounded by the main body member 211). In other words, the fitting member 212 is a member that can be separated from the main body member 211. By configuring the attachment portion 210 with the main body member 211 and the fitting member 212 that are separable from each other in this way, the hood 200 can be easily attached and detached from the lens unit 120. In particular, even when later attaching the hood 200 to a projector 100 installed on a ceiling, work efficiency can be improved by first positioning the fitting member 212 in an appropriate position and then attaching the main body member 211. Furthermore, if it becomes necessary to adjust the projection direction of the projector 100, the hood 200 can be easily temporarily removed and reattached, resulting in excellent maintainability.

[0009] In the hood 200 according to the present invention, the opening 224 of the shielding portion 220 preferably widens as it progresses further along the optical axis of the projection lens 122. Since light (image light) projected from the projection lens 122 generally spreads along the optical axis, the shielding portion 220 is preferably structured to match this spread of light. This allows the shielding portion 220 to effectively block only the line of sight toward the projection lens 122 without blocking the light from the projection lens 122.

[0010] The hood 200 according to the present invention may be compatible with the projector 100 that includes the lens unit 120. The lens unit 120 includes a light guide 121 for changing the direction of light travel and a projection lens 122 provided at the output end of the light guide 121. By attaching such a lens unit 120 to the projector 100, the path of light projected from the projector 100 can be adjusted by the light guide 121. In this case, the hood 200 according to the present invention is preferably configured such that the attachment portion 210 can be attached to the lens unit 120 of the projector 100. Attaching the hood 200 to the lens unit 120 of the projector 100 makes it easier to attach and detach the hood 200 than attaching the hood 200 to the main body of the projector 100.

[0011] In a further embodiment of the present invention, the hood 200 may be formed three-dimensionally by folding a single sheet-like member. By providing the hood 200 with such a simple structure, the manufacturing cost can be reduced.

[0012] According to the present invention, it is possible to prevent the light source reflected in the projection lens of the projector from being visible to the audience.

[0013] FIG. 1 is a side view of a hood according to an embodiment of the present invention, showing the state before the hood is attached to a projector. FIG. 2 is a side view of a hood according to an embodiment of the present invention, showing the state after the hood is attached to a projector. FIG. 3 is a side view and a front view of the hood according to an embodiment of the present invention, showing the state with the fitting member removed. FIG. 4 is a perspective view of a hood according to an embodiment of the present invention. FIG. 5 is a side view of a hood according to a reference embodiment, showing the state before the hood is attached to a projector. FIG. 6 is a side view of a hood according to a reference embodiment, showing the state after the hood is attached to a projector. FIG. 7 is an exploded view of a hood according to a reference embodiment. FIG. 8 is a perspective view of a hood according to a reference embodiment after it has been assembled.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes appropriate modifications of the embodiments described below within the scope obvious to those skilled in the art.

[0015] First, an embodiment of a hood 200 according to the present invention will be described with reference to Figures 1 to 4. As shown in Figures 1 and 2, the hood 200 according to the present embodiment is intended to be attached to a projector 100 equipped with a lens unit 120.

[0016] 1 , when the hood 200 is not attached to the projector 100, if an audience member views the projector 100 from a direction perpendicular to the optical axis L of the projection lens 122, the audience member may directly view the projection lens 122 of the projector 100. In this case, when image light is projected from the projector 100, a light source (not shown) inside the projector 100 may be reflected by the projection lens 122, causing strong light to enter the audience member's eyes. In this case, depending on the audience member's standing position, it may appear as if strong light is being emitted from the projection lens 122 of the projector 100, making the projector 100 seem more noticeable, and this may prevent the audience member from concentrating on the image light projected from the projector 100.

[0017] 2, when the hood 200 is attached to the projector 100, the hood 200 can block the line of sight of the projection lens 122 from a direction perpendicular to the optical axis L of the projection lens 122. By attaching the hood 200 to the projector 100 in this way, the blind spot of the projection lens 122 of the projector 100 (the angle at which the projection lens 122 cannot be directly viewed) increases, and therefore the light source reflected on the projection lens 122 can be prevented from being viewed by the audience.

[0018] First, the projector 100 to which the hood 200 is to be attached will be described. Basically, a commercially available, publicly known projector 100 can be used. The hood 200 according to the embodiment shown in FIGS. 1 to 4 is intended to be attached to the projector 100 fixed to the ceiling, as shown in FIGS. 1 and 2. The projector 100 is fixed to the ceiling of an indoor space and is configured to project image light onto a wall surface. The projector 100 includes a projector body 110 and a lens unit 120 attached to the projector body 110. The lens unit 120 is detachable from the projector body 110. When the lens unit 120 is not attached to the projector 100, a projection lens 122 is attached directly to the projector body 110 instead of the lens unit 120.

[0019] Although not shown, the projector body 110 mainly incorporates a light source and an imaging device (e.g., a liquid crystal panel or DLP chip) for processing video signals and modulating light from the light source. The projector may be of any of the following types: LCD (liquid crystal display), DLP (digital light processing), LCoS (liquid crystal on silicon), laser, and LED. The lens unit 120 also includes a light guide 121 for changing the direction of travel of the image light generated by the projector body 110, and a projection lens 122 provided at the output end of the light guide 121. In this embodiment, the light guide 121 of the lens unit 120 is configured to reverse the output direction of the image light from the projector body 110 by 180 degrees. In other words, when the lens unit 120 is removed and the projection lens 122 is directly attached to the projector body 110, the image light from the projector body 110 is projected toward the right side in Fig. 1, but when the lens unit 120 is attached to the projector body 110, the image light from the projector body 110 is guided by the light guiding section 121 and projected toward the left side in Fig. 1. Note that it is possible to appropriately attach lens units 120 with light guiding sections 121 of different shapes to the projector body 110, thereby making it possible to arbitrarily adjust the projection direction of the image light according to the shape of the light guiding section 121.

[0020] 1 and 2, the light guide section 121 of the lens unit 120 has a first section 121a to a fourth section 121d. The first section 121a is a section including a mirror or the like that changes the path of the image light emitted from the projector body 110 by 90 degrees. The second section 121b is a section through which the image light whose path has been changed by the first section 121a travels straight. The third section 121c is a section including a mirror or the like that changes the path of the image light that has passed through the second section 121b by 90 degrees. The fourth section 121d is a section through which the image light whose path has been changed by the third section 121c travels straight to the projection lens 122. The projection lens 122 is attached to the tip of the fourth section 121d. In this way, the light guide section 121 of the lens unit 120 reverses the traveling direction of the image light emitted from the projector body 110 by 180 degrees. Furthermore, the fourth section 121d of the lens unit 120 extends parallel to the projection direction of the image light, that is, the fourth section 121d determines the projection direction of the image light. Furthermore, as shown in FIG. 1 , a gap is provided between the fourth section 121d and the projector body 110. A hood 200, which will be described later, is attached using this gap between the fourth section 121d and the projector body 110.

[0021] Next, a specific configuration of the hood 200 will be described. As shown in FIGS. 1 to 4 , the hood 200 according to this embodiment basically includes an attachment portion 210 and a shielding portion 220. The attachment portion 210 is a portion for detachably attaching the hood 200 to the projector 100. The shielding portion 220 is fixed to the attachment portion 210 and is a portion for covering and concealing mainly the projection lens 122 of the projector body 110, thereby blocking the view of the audience from the projection lens 122. There are no particular limitations on the material constituting the hood 200 as long as it has light-blocking properties, and the hood 200 can be made using known materials such as plastic, metal, paper, and wood.

[0022] In this embodiment, the attachment portion 210 of the hood 200 is configured to be attachable to the light guiding portion 121 of the lens unit 120 of the projector 100. More specifically, as shown in Figures 1 and 2, the attachment portion 210 of the hood 200 is fixed to the fourth portion 121d of the light guiding portion 121 of the lens unit 120, which is the final portion through which the image light travels in a straight line. As described above, a gap is provided between the fourth portion 121d of the light guiding portion 121 and the projector body 110, and therefore, the attachment portion 210 can be fixed to the projector 100 by inserting a part of the attachment portion 210 into this gap.

[0023] FIG. 3 shows a specific configuration of the attachment portion 210 of the hood 200. As shown in FIG. 3, the attachment portion 210 of the hood 200 includes a main body member 211 and a fitting member 212. The main body member 211 is frame-shaped and surrounds the light guide portion 121 of the lens unit 120, particularly the fourth portion 121d, leaving a portion open. Specifically, because the light guide portion 121 of the lens unit 120 (particularly the fourth portion 121d) has a square cross section, the main body member 211 of the attachment portion 210 of the hood 200 is U-shaped and surrounds three sides of the light guide portion 121, with the remaining side of the light guide portion 121 being open. In the illustrated example, the main body member 211 surrounds the bottom, left, and right sides of the light guide portion 121, and the top side of the light guide portion 121 is open. On the other hand, fitting member 212 is fitted into main body member 211 so as to abut against at least the portion not surrounded by main body member 211. As described above, since the upper side of light guiding section 121 is not surrounded by main body member 211, fitting member 212 abuts against at least the upper side of light guiding section 121.

[0024] More specifically, main body member 211 of attachment portion 210 of hood 200 is U-shaped and has a lower frame 211a, a left outer frame 211b, and a right outer frame 211c, and these respective portions surround the lower, left, and right sides of light guiding portion 121 (particularly fourth portion 121d) of lens unit 120. On the other hand, fitting member 212 of attachment portion 210 of hood 200 is U-shaped in the opposite direction to main body member 211 and has an upper frame 212a, a left inner frame 212b, and a right inner frame 212c, and these respective portions surround the upper, left, and right sides of light guiding portion 121 of lens unit 120. When the main body member 211 and the fitting member 212 having such a structure are fitted together, as shown in FIG. 3B , the left inner frame 212b and the right inner frame 212c of the fitting member 212 are inscribed in the left outer frame 211b and the right outer frame 211c of the main body member 211, respectively. That is, the left inner frame 212b of the fitting member 212 overlaps the inside of the left outer frame 211b of the main body member 211, and the right inner frame 212c of the fitting member 212 overlaps the inside of the right outer frame 211c of the main body member 211. Thereafter, with the fitting member 212 fitted into the main body member 211, the two are fixed together using fasteners 213 such as screws and nuts. In the illustrated example, the overlapping portions of the main body member 211 and the fitting member 212 are fixed together by the fasteners 213. That is, the overlapping portion of the left outer frame 211b of the main body member 211 and the left inner frame 212b of the fitting member 212 is screwed together, and the overlapping portion of the right outer frame 211c of the main body member 211 and the right inner frame 212c of the fitting member 212 is screwed together.

[0025] To attach the mounting portion 210 having the above structure to the lens unit 120 of the projector 100, for example, first, the fitting member 212 of the mounting portion 210 is inserted into the gap between the projector body 110 and the light guide portion 121 (particularly the fourth portion 121d) of the lens unit 120. Then, the main body member 211 of the mounting portion 210 is lifted from below, and the fitting member 212 is fitted into this main body member 211. Finally, the main body member 211 and the fitting member 212 are fixed together using fasteners 213. This makes it possible to attach the hood 200 to an existing projector 100 at a later time.

[0026] A shielding portion 220 is fixed to a main body member 211 of the mounting portion 210 of the hood 200. In other words, the shielding portion 220 is integrated with the main body member 211 of the mounting portion 210. As shown in FIGS. 3 and 4 , the shielding portion 220 extends from the main body member 211 of the mounting portion 210 in the direction of the optical axis L of the projection lens 122 of the projector 100, and has an opening 224 formed therein through which the image light projected from the projection lens 122 passes. Furthermore, the shielding portion 220 has shielding plates 221 to 223 provided around the opening 224 to block the view of the audience from the projection lens 122. Specifically, the shielding portion 220 has a lower shielding plate 221, a left shielding plate 222, and a right shielding plate 223. The lower shielding plate 221 is fixed to a lower frame 211a of the main body member 211 of the mounting portion 210, the left shielding plate 222 is fixed to a left outer frame 211b of the main body member 211 of the mounting portion 210, and the right shielding plate 223 is fixed to a right outer frame 211c of the main body member 211 of the mounting portion 210. The shielding plates 221 to 223 may be fixed by a non-detachable method such as adhesive or welding.

[0027] Furthermore, the opening 224 between the shielding plates 221-223 is shaped to widen as it advances in the optical axis direction of the image light. As shown in the perspective view of FIG. 4, each of the shielding plates 221-223 has a slope that widens outward. In other words, the opening 224 between the shielding plates 221-223 is inverted tapered and widens toward the front. Since the image light projected from the projection lens 122 of the projector 100 generally widens along the optical axis direction, it is preferable that the shielding portion 220 be structured to match this light widening. This allows the shielding portion 220 to effectively block only the viewer's line of sight toward the projection lens 122 without blocking the light from the projection lens 122.

[0028] 3, the extension length of the shielding portion 220 along the optical axis direction is indicated by the symbol E. The extension length E of the shielding portion 220 is preferably 50 mm or more, more preferably 60 mm or more, or even 70 mm or more. Specifically, the extension length E of the shielding portion 220 is preferably 50 to 100 mm.

[0029] 2, when the hood 200 is attached to the projector 100, it is preferable that the upper part of the shielding portion 220 of the hood 200 be in close contact with the projector body 110 or be close to it with almost no gap. As described above, the shielding portion 220 of the hood 200 has the lower shielding plate 221, left shielding plate 222, and right shielding plate 223, but does not have a portion corresponding to the upper shielding plate. Therefore, the upper edges of the left shielding plate 222 and the right shielding plate 223 of the shielding portion 220 can be in close contact with or close to the projector body 110, respectively. Note that even if there is a gap between the upper part of the shielding portion 220 of the hood 200 and the projector body 110, it is preferable that the gap be 10 mm or less. In this way, by bringing the shielding portion 220 of the hood 200 into close contact with or close to the projector body 110 , the projection lens 122 provided at the tip of the lens unit 120 can be effectively covered and hidden by the hood 200 .

[0030] As shown in FIGS. 1 and 2 , in this embodiment, the optical axis L of the projection lens 122 extends substantially horizontally toward the wall surface. This "optical axis L" is a straight line connecting the center of the projection lens 122 and the focal point, and corresponds to a virtual ray representing the light beam. FIG. 2 also shows the line of sight of the projection lens 122 from a direction perpendicular to the optical axis L. As shown in FIG. 2 , when the hood 200 is attached to the projector 100, the hood 200 blocks the line of sight of the projection lens 122 from a direction perpendicular to the optical axis L. In other words, when the projection lens 122 is viewed from a position where the optical axis L and the line of sight of an audience or the like intersect perpendicularly at the projection lens 122, the hood 200 blocks the line of sight of the audience or the like. Naturally, the projection lens 122 may be visible depending on the audience's viewpoint. However, for example, from a position directly below or beside the projection lens 122, the hood 200 blocks the audience's line of sight of the projection lens 122. In this way, by attaching the hood 200 to the projector 100, it is possible to prevent the light source inside the projector 100 reflected in the projection lens 122 from being visible to the audience.

[0031] Next, a reference embodiment of the hood 200 will be described with reference to Fig. 5 to Fig. 8. As shown in Fig. 5 and Fig. 6, the hood 200 is intended to be attached to a projector 100 that does not have a lens unit 120.

[0032] 5 and 6, the projector 100 is fixed to the ceiling of an indoor space and is configured to project image light onto the floor surface. This projector 100 does not include the lens unit 120 as in the examples shown in FIGS. 1 and 2, but has a projection lens 122 attached directly to the projector body 110. As in the above-mentioned projector body 110, the projector body 110 mainly contains a light source and an imaging device (e.g., a liquid crystal panel or DLP chip) for processing an image signal and modulating the light from the light source, and the image light generated by this imaging device is projected onto the floor surface from the projection lens 122.

[0033] As shown in FIGS. 6 to 8 , the hood 200 according to this embodiment is formed three-dimensionally by folding a single sheet-like member. FIG. 7 shows a development view of the hood 200 according to this embodiment, and FIG. 8 shows the hood 200 according to this embodiment after three-dimensional molding. The hood 200 basically includes an attachment portion 210 and a shielding portion 220. The attachment portion 210 is a portion for detachably attaching the hood 200 to the projector 100. The shielding portion 220 is fixed to the attachment portion 210 and is a portion for covering mainly the projection lens 122 of the projector body 110, thereby blocking the viewer's line of sight of the projection lens 122. There are no particular limitations on the material constituting the hood 200 as long as it has light-blocking properties. However, because the hood 200 must be formed by folding as described above, it is preferable to fabricate the hood 200 using a known flexible material such as plastic, paper, or wood.

[0034] As shown in FIG. 7 , when the hood 200 is unfolded, it forms a substantially C-shaped sheet-like member. This sheet-like member has an opening 224 formed in its center and a partial cutout 225 formed to connect to the opening 224. Therefore, the hood 200 is C-shaped when unfolded. Furthermore, a plurality of attachment tabs 214 protrude from the C-shaped sheet-like member toward the center of the opening 224. Then, by joining the edges of the cutouts 225 of the sheet-like member, the hood 200 is formed into a truncated cone-shaped member with the central opening 224, as shown in FIG. 8 . The method for joining the cutouts 225 of the sheet-like member is not particularly limited, and may be any method such as joining using an adhesive, fasteners, or welding. Furthermore, the claws 214 of the hood 200 are bent toward the center of the central opening 224. In this way, the claws 214 of the hood 200 function as attachment portions 210 for attaching the hood 200 to the projector 100. The sheet-like portion of the hood 200 other than the claw portion 214 functions as a shielding portion 220 for covering the projection lens 122 .

[0035] 7, the width of the shielding portion 220 of the hood 200 is indicated by the symbol W. The width W of the shielding portion 220 is the shortest distance from the opening 224 of the hood 200 to the outer edge. The width W of the shielding portion 220 is preferably 50 mm or more, and more preferably 60 mm or more or 70 mm or more. Specifically, the width W of the shielding portion 220 is preferably 50 to 100 mm.

[0036] In this embodiment, the attachment portion 210 of the hood 200 is configured to be directly attached to the projection lens 122 of the projector 100. Specifically, by inserting the claw portions 214, which function as the attachment portion 210 of the hood 200, into the base of the projection lens 122, the hood 200 is attached so as to surround the periphery of the projection lens 122, as shown in FIG. 5 . The shielding portion 220 of the hood 200 extends in the same direction as the optical axis L of the projection lens 122 and functions to block the view of an audience member toward the projection lens 122. In this way, the hood 200 according to this embodiment can block the view of an audience member toward the projection lens 122 from a direction perpendicular to the optical axis L. In other words, when the projection lens 122 is viewed from a position where the optical axis L and the view of an audience member or the like intersect perpendicularly at the projection lens 122, the view of the audience member or the like is blocked by the hood 200. Naturally, the projection lens 122 may be visible depending on the audience's viewpoint, such as directly below the projector body 110, but the hood 200 can block the audience's view from positions directly to the side or diagonally below the projection lens 122, for example.

[0037] In the above specification, in order to express the contents of the present invention, embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to the above embodiments, and includes modifications and improvements that are obvious to those skilled in the art based on the matters described in the present specification. Furthermore, the reference embodiments described in the present specification do not constitute a waiver of the right to obtain a patent, and the right to modify these reference embodiments into embodiments of the present invention and obtain a patent is reserved.

[0038] REFERENCE SIGNS LIST 100...Projector 110...Projector body 120...Lens unit 121...Light guide section 122...Projection lens 200...Hood 210...Mounting section 211...Main body member 211a...Lower frame 211b...Left outer frame 211c...Right outer frame 212...Fitting member 212a...Upper frame 212b...Left inner frame 212c...Right inner frame 213...Fastener 214...Claw section 220...Shielding section 221...Lower shielding plate 222...Left shielding plate 223...Right shielding plate 224...Opening 225...Notch L...Optical axis

Claims

1. A projector hood that is removably attachable to a projector around a projection lens, and that is configured to block at least the line of sight toward the projection lens from a direction perpendicular to the optical axis of the projection lens without blocking the light projected from the projection lens, wherein the projector is equipped with a lens unit including a light guiding section for changing the direction of travel of the light, and the projection lens provided at the output end of the light guiding section, and the projector hood comprises: an attachment section that is removably attached to the lens unit of the projector; and a shielding section that extends from the attachment section in the direction of the optical axis of the projection lens, has an opening through which the light passes, and is configured to block the line of sight, and the attachment section has: a main body member to which the shielding section is fixed, and that is configured to surround the periphery of the lens unit leaving a partial space open; and a fitting member that is fitted into the main body member so as to abut against the partial periphery of the lens unit.

2. The hood according to claim 2, wherein the opening of the shielding portion widens as it advances in the optical axis direction.

Images