JPH0811223A - Optical element and its molding method - Google Patents

Abstract

PURPOSE:To provide an optical element and its molding method wherein a cost of a mold member for molding can be reduced, an effective using sphere part of a lens can be processed evenly, even as to positions of the ridge lines of the lenses coming into contact with each other further, processing at an arbitrary position is possible and the processing of an asymmetrical and nonspherical surface is possible. CONSTITUTION:In a molding method of an optical element 1, a plurality of functional surfaces 11 are transferred and formed on the surface flush with the optical element by transferring a surface form which is an optically functional surface of a mold member for molding of an optical element l and as for the surface form of the mold member for molding, it is processed so that the edge of a blade of a diamond bit having the fixed radius of curvature is faced on the outer circumferential direction, the bit is turned and the mold member for molding is engraved, the blade is set up so that its radius of curvature is approximately at most 3mm, and its perfect roundness is approximately at most 1 micron and turned by setting up a turning radius at most about 3mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element molded by using a molding die member and a molding method thereof.
The present invention relates to an optical element such as a secondary imaging lens for a focus detection device of a camera and a method for molding the same.

[0002]

2. Description of the Related Art Conventionally, a secondary imaging lens used in a focus detection device such as a camera has been molded by the following two methods. (First Conventional Example) In the first conventional example, as a molding die member, a plurality of rod-shaped mirror-finished pieces whose tip is processed into a predetermined lens shape by a grinding / polishing method or a cutting method are manufactured. Separately, a polished mirror surface piece is incorporated into a frame piece manufactured separately to form a unit, which is incorporated into a molding die to form a lens. FIG. 17 shows the method of the first conventional example. In FIG. 17, the tip portion 25 of the rod-shaped mirror surface piece 23 is processed into a predetermined lens optical surface shape by a grinding / polishing method or a cutting method, and a rod-shaped hole is provided in a frame piece 24 separately manufactured from these. By incorporating the mirror surface piece 23, the secondary imaging lens and the like have been molded.

(Second Conventional Example) The method of the second conventional example is as follows.
A molding die member (mirror surface piece) having an integral structure is fixed to the main shaft portion of a lathe machine for precision processing, and the optical axis of the optical function surface of the plurality of lenses provided on this main shaft is aligned with the rotation axis of the main shaft. Each lens transfer surface of the mirror surface piece is manufactured by lathe processing with a diamond bite, and the processed mirror surface piece is incorporated into a molding die to form a lens. FIG. 18 shows the method of the second conventional example. In FIG. 18A, a mirror surface piece 15 is attached to the main shaft 13 of a lathe machine for precision processing, and the lens transfer surface is processed by rotating the mirror surface piece 15. At the time of processing, the rotary spindle 13 is moved in the Z direction along the rotary axis together with the rotating operation of the lathe, and the direction X orthogonal to the Z direction of the diamond cutting tool 26.
The method of processing the mirror surface piece by controlling the feeding operation of the mirror is adopted.

[0004]

However, the above-mentioned conventional examples have the following drawbacks. (Problems in First Conventional Example) Problems of the first conventional technique will be described with reference to FIG. FIG. 1 shows an example of a molded article of an eight-eye secondary imaging lens as an optical element according to this embodiment. In FIG. 1, when observing the gap C between the lenses 11 which are not in contact with each other, when the optical element is molded by the method of the first conventional example, the strength of the frame piece of the molding die is maintained at a predetermined value or more. Therefore, it is necessary to set the thickness to a certain value or more. As a result, the thickness of the frame piece becomes an obstacle and the secondary imaging lens cannot be downsized. Furthermore, the focus detection optical system including the secondary imaging lens,
The size of the sensor that photoelectrically converts the image of the subject cannot be reduced.
Increasing the size of the camera itself equipped with the secondary imaging lens and increasing cost have been problems that cannot be avoided.

Further, as shown in FIG. 17, a rod-shaped mirror surface piece 23
However, there is a drawback in that the accuracy of the finished product cannot be guaranteed due to an error between the mirror-finished frame and the frame piece. FIG. 22 is a diagram showing a state of the focus detection optical system when the relative positional accuracy between the secondary imaging lens and the sensor is correct. In FIG. 22, photoelectric conversion sensors 41 and 42 arranged in parallel to the secondary image formation surface are provided on one side of the secondary image formation lens 40, and photoelectric conversion sensors 41 and 42 are provided on the other side. The field of view 43 on the primary image forming plane viewed through the secondary image forming lens 40 is reproduced. Here, the secondary imaging lens 4 composed of a pair of left and right
When 0 is arranged at the correct position, as shown in FIG. 22, focus detection is normally performed on the result of photoelectric conversion of each pixel of each photoelectric conversion sensor 41, 42.

On the other hand, FIG. 23 is a diagram showing a state of the focus detection optical system in the case where an error in the vertical direction occurs relative to the pair of left and right secondary imaging lenses 40 when viewed from the drawing. In FIG. 23, as in FIG. 22, photoelectric conversion sensors 41 and 42 arranged in parallel with the secondary imaging surface are provided on one side with the secondary imaging lens 40 interposed therebetween, and on the other side, The field of view 43 on the primary image forming surface seen through the secondary image forming lens 40 of the photoelectric conversion sensors 41 and 42 is reproduced. Also, FIG.
3, the field of view 44 on the primary imaging surface seen through the secondary imaging lens 40 of the photoelectric conversion sensor 41 and the primary imaging seen through the secondary imaging lens 40 of the photoelectric conversion sensor 42. The field of view 45 on the surface is reproduced. That is, when a vertical error occurs relatively in the pair of left and right secondary imaging lenses 40, the photoelectric conversion sensors 41 and 42 see different visual fields 44 and 45 on the primary imaging plane. Therefore, the correct focus detection operation cannot be guaranteed. As described above, in the first conventional example, the accuracy when the rod-shaped mirror surface piece is incorporated in the frame piece cannot be stabilized, and the yield of the molding die as a non-defective product is deteriorated, which makes it unsuitable for mass production. There were also points.

A further problem is that the ridge line position between the lenses that are in contact with each other is limited by the processing ability of the frame piece. FIG. 24 is a diagram showing a case where the effective use area portion of the secondary imaging lens is displaced from the central portion, and the effective use area portion of the lens is shown by hatching in the figure. This FIG. 24
In the case of 1, the effective use area portion is deviated from the center portion of the lens to the right side in the figure. This is the state of the lens that occurs when focus detection is performed in a field of view other than the central portion of the shooting screen, such as a range-finding region of a wide field of view, multi-point range finding, etc., but in the method of the first conventional example, In this case, a molding die for molding the secondary imaging lens cannot be manufactured. The reason for this will be described with reference to FIG. 20. As shown in FIG. 20, when the frame piece 24 is ground by the grinder grindstone 27, the grinder grindstone 27 is a tool having a certain predetermined turning radius. This is because the region 29 cannot be processed, and as a result, the rod-shaped mirror surface piece for the right lens shown in FIG. 24 cannot be incorporated in the frame piece 24. That is, the lens shape effective in manufacturing the frame piece in the method of the first conventional example is only in the case where the ridge lines are smoothly connected as shown in FIG. When it comes off, the effective use area portion is narrowed as can be seen from the hatched portion in FIG. 25, which causes a problem.

(Problems of Second Conventional Example) Next, problems of the second conventional technique will be described with reference to FIG. FIG.
An example of a lathe processing mark generated on the secondary imaging lens when the method of the second conventional example is used is shown in FIG. As can be seen from FIG. 21, in the effective use region portion 30, the cutting trace 32 has no contrast. As a result, since the imaging performance on the surface of the photoelectric conversion sensor does not have contrast, the asymmetry of the processing mark 32 appears as an error during focus detection.

Further, during lathe processing, as shown in FIG. 21, a cutting residue 31 called a navel is formed at the center of the lens without stopping. The cutting residue 31 adversely affects the imaging performance on the surface of the photoelectric conversion sensor and causes a problem in focus detection. A further drawback is that
As in the case of the first conventional example, the ridgeline position between the lenses in contact with each other is limited by the processing ability of the frame piece, and cannot be set at an arbitrary position. That is, even if the method of the second conventional example is adopted, the secondary imaging lens having the shape as shown in FIG. 24 cannot be manufactured, and as a result, as shown in FIG.
As described above, the effective use area portion is narrowed.

Further, there is a problem that the precision of the optical axis alignment between the main axis of the lathe machine for precision machining and the molding die of the secondary imaging lens is not stable. This problem causes a difference in the visual fields viewed by the left and right photoelectric conversion sensors as shown in FIG. 23 of the first conventional example. In addition, in the method of the second conventional example, asymmetrical aspherical surface processing of a lens is impossible, and it is necessary to process a part other than the effective use area part, and the tool life as a processing tool is short. However, there were some problems in terms of production and function.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to prevent deformation of a frame piece due to insufficient strength and reduce the cost of a mirror piece, and a molding method thereof. To provide.
Further, an optical element and its molding method capable of uniformly processing the effective use area of the lens and further processing the ridgeline position of the lenses in contact with each other at any position, which enables asymmetrical aspherical surface processing. To provide.

[0012]

In order to solve the above-mentioned problems and to achieve the object, a method of molding an optical element according to the present invention comprises:
A method of molding an optical element, comprising transferring a plurality of optical functional surfaces onto the same surface of the optical element by transferring the surface shape of the molding die member, which is the optical functional surface, to the material of the optical element. The surface shape of the molding die member is characterized in that the cutting edge of a diamond cutting tool having a predetermined radius of curvature is oriented in the outer peripheral direction, and the cutting tool is rotated to engrave the molding die member. There is.

Preferably, the radius of curvature of the cutting edge is about 3 mm or less, the roundness is set to about 1 micron or less, and the turning radius of the cutting edge is set to about 3 mm or less to rotate. Is characterized by. Further, preferably, the optical element according to the present invention is characterized by being molded by the method for molding an optical element according to claim 1 or 2.

Further, it is preferable that the optical element is a secondary imaging lens for a focus detection device mounted on a camera. Further, preferably, the plurality of optical function surfaces of the optical element are further formed by a plurality of lenses. Further, preferably, the ridgeline formed by the contact of the plurality of lenses has a discontinuous shape.

Preferably, all or some of the plurality of optical functional surfaces of the optical element have an asymmetrical aspherical shape. Further, preferably, all or a part of the plurality of optical function surfaces of the optical element is constituted only by its effective use area portion. Further, preferably, the interval between the plurality of optical function surfaces of the optical element is set to 0.6 mm or less.

[0016]

As described above, according to the present invention, the fly-cut process is carried out so that the cutting edge of a diamond cutting tool having a predetermined radius of curvature is directed toward the outer peripheral direction and the cutting tool is rotated to engrave a molding die member. Depending on the method, the mirror surface piece as a molding die member and the frame piece can be integrated, and by processing the surface shape of multiple optical function surfaces, deformation due to insufficient strength of the frame piece can be prevented, and the cost of the mirror surface piece can be reduced. Can be reduced.

Further, it is possible to uniformly process the lens effective use area portion of the cutting eye, and it is possible to process the ridge line positions of the lenses that are in contact with each other at any position, and it is possible to perform asymmetrical aspherical surface processing.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1A is a view showing a molded product of a secondary imaging lens used in the focus detection device for a camera of the embodiment according to the present invention, and FIG. 1B is a view of A in FIG. FIG. 7 is a cross-sectional view taken along arrow A. 2A is a view showing a mirror surface piece as a molding die member for molding the secondary imaging lens of FIG. 1, and FIG. 2B is FIG. 2A.
It is a BB arrow sectional drawing of. In FIG. 1, the secondary imaging lens 1 is a compound lens having a plurality of lens portions 11, is molded using a plastic material such as acrylic (PMMA) resin, and the cross section of the lens portion 11 is shown in FIG. To form a convex surface. In addition, in FIG.
The mirror surface piece 15 as a molding die member for molding the next imaging lens 1 corresponds to the lens portion 11 as shown in the cross section of FIG. 2B in order to transfer-mold a plurality of lens portions 11. To form a concave surface 11 '.

FIG. 3 is a diagram showing a machine tool for performing a cutting process or the like on a mirror surface piece 15 for transfer molding of the secondary imaging lens 1 and a machining state thereof. Further, FIG. 4 shows S of FIG.
It is an enlarged view which shows the detail of 1 part. 3 and 4, the machine tool 5 is an ultra-precision NC processing machine. This NC
The processing machine 5 has tables 3, 4 and 5 which are slidable in three axial directions of X axis, Y axis and Z axis, and has a spindle 13 at the tip of the Z direction in the traveling direction Z shown in FIG. It is a machine. Further, the processing machine 5 has a configuration in which the position of each axis (X, Y, Z) is detected by a laser interferometer and can be precisely positioned (for example, resolution is 0.01 micron or less). The main shaft 13 is a hydrostatic bearing and has extremely high rotational accuracy (for example, rotational reproducibility is 0.05 micron or less). The cutting tool holder 19 is attached to the tip of the main shaft 13, and the diamond cutting edge 18 of the diamond cutting tool 17 is attached to the cutting tool holder 19 so as to face the outer peripheral direction, so that the cutting edge 18 rotates in the direction 14 around the Z axis. FIG.
As shown in (a), the diamond cutting edge 18 at the tip of the diamond cutting tool is attached so that the cutting edge faces the outer peripheral direction, and serves as the lens transfer surface of the mirror surface piece 15 in the drawing.
In order to remove the portion indicated by 2, the mirror surface piece is rotated while moving in the three-axis directions, and three-dimensional processing is performed on the mirror surface piece. Figure 4 (b) shows
It is sectional drawing seen from the arrow S2 direction of Fig.4 (a). FIG.
As shown in (b), the diamond cutting edge 18 is
It has a flat plate shape.

FIG. 5 is a view showing the shape of the cutting tool when the cutting edge 18 is attached to the diamond cutting tool holder 17. In FIG. 5, the shape f of the cutting edge 18 at the tip is such that the radius of curvature R of the surface is 3 mm or less and the roundness is 1 micron or less, and the turning radius e of the cutting edge is set to 3 mm or less. Further, the shank portion extending from the cutting edge to the holder 17 is formed in two steps, and the shank portion tip diameter h is a diameter φ2.6.
Each dimension is determined so that the length g is 10 mm or less when the length is less than mm.

6 and 7 are both NCs shown in FIG.
It is a figure which shows the processed surface after performing a cutting process to the mirror surface piece by a processing machine. Especially, FIG. 6 shows the processing marks which remain in the X-axis direction, and FIG. 7 shows the processing marks which remain in the Z-axis direction. . As shown in FIGS. 6 and 7, in the fly-cut method in which the surface is processed by rotating the diamond cutting tool having the shape shown in FIG. 5 of the present embodiment, the processed surface of the mirror-finished piece is a streaky subdivided processing. A scar 21 remains. The intervals of the processing marks 21 are set so that the surface roughness in the Y-axis direction (direction normal to the drawing) is kept within a predetermined accuracy allowable range. Specifically, when it is desired to improve the accuracy of the surface roughness, the machining time is set longer than before and the numerical control of the NC processing machine is performed so that the shape of the processing mark is further subdivided. At the time of processing, the processing is continuously performed along the direction 22 perpendicular to the processing mark 21, and when the processing of one line along the direction 22 is completed, the next adjacent line is processed similarly. , The entire lens transfer surface is finished. The processing width 20 of one line is shown in FIGS. 6 and 7. (Processing Procedure for Mirror Surface Piece) Next, the processing procedure for the mirror surface piece will be described with reference to FIG.

FIG. 8 is a view for explaining the processing procedure of the mirror surface piece. In FIG. 8, focusing on the lens transfer surface having the center 101, first, a processing line (indicated by arrows 110 and 111 in the figure) for subdividing in the X-axis direction orthogonal to the cross section parallel to the X-axis passing through the center 101. , 112 ...) are set.
The interval between the processing lines is set so that the surface roughness in the X-axis direction falls within a predetermined allowable range. For example, in this embodiment, the allowable range is set to 0.08 micron or less. The machining is performed from the machining start line 110 of this machining line, but the tool tip R with respect to the machining line so that the cutting tool tip passes through this machining line 110.
The machining data is created by calculating the coordinates of each machining point, taking into consideration the change of the contact point. Based on the created data, NC movement of the NC processing machine in each of the X-axis, Y-axis, and Z-axis is NC controlled, and one line is processed. When the processing of this one line is completed, the process moves to the next line 111 and the same processing is performed. Thus, by finishing the processing of all the lines subdivided in the X-axis direction from the line 110 to the lines 111, 112, ..., One lens transfer surface having the center 101 can be formed. Then, the cutting tool is moved to the processing position of the lens transfer surface having the center 102, and processing is performed according to the above procedure. Similarly, the center 103
By sequentially processing the lens transfer surfaces each having .about.108, a mirror surface piece for molding the secondary imaging lens of this embodiment is completed.

By the above-mentioned processing procedure, the lens transfer surface is processed on one mirror surface piece of a plurality of lenses to manufacture a mirror surface piece for molding a secondary imaging lens as a compound lens,
This mirror surface piece is used as molding dies 51 and 56 to be described later to mold a lens to mold a secondary imaging lens. As described above, by manufacturing the mirror-finished frame by the fly-cut method, the ridgeline positions of the adjacent lenses can be arbitrarily set, and a lens having an asymmetrical aspherical shape can be formed. As the material of the mirror surface piece, a material that can be cut with a diamond bite and can withstand a predetermined molding strength is most suitable, and examples thereof include phosphor bronze, pure copper, electroless nickel plating, brass and the like. Also, during processing,
The life of the diamond tool itself can be extended by processing only the effective use area of the lens. Further, it becomes possible to process a lens having a very narrow interval such that the inter-lens distance C shown in FIG. 1 is 0.6 mm or less.

By using the mirror surface piece manufactured by the above procedure, it is possible to mold from the injection molding die 51 as shown in FIG. 9 and FIG.
It is also possible to mold from a compression molding die 56 as shown in FIG. 9 and 10 are views showing a lens molding method by an injection molding method. In the case of injection molding, an injection molding apparatus 52 including an injection unit 53 for injecting a lens material into a mold and a mold clamping unit 54 is used, and a mold 51 is provided with a liner sprue 55. The material is poured and the lens 1 as shown in FIG. 10 is formed. 11 to 13 are views showing a lens molding method by a compression molding method. In the case of compression molding, the heated compression molding blank 58 is mounted on the compression molding die 56 of the ejecting unit 59, and the mirror surface piece 15 is attached to the portion that comes into contact when compressed in the unit that receives the compression molding device. After installation, the lens 1 is molded by compression as shown in FIG.

By the lens molding method described above, FIG.
A lens which cannot be molded by the conventional technique as shown in FIG. 16 can be manufactured. FIG. 14 is a diagram showing an example of the secondary imaging lens in the case where the ridge spacing of the lenses in contact with each other is set to a position that cannot be obtained by the conventional processing method. Further, FIG. 15 is a diagram showing an example of a secondary imaging lens in the case of setting an asymmetrical aspherical shape which is impossible with the method of the second conventional example. FIG. 16 is a diagram showing an example of a secondary imaging lens in the case of processing only the effective use area portion of the lens, which is impossible with the method of the second conventional example.

The present invention can be applied to modifications and variations of the above embodiments without departing from the spirit of the present invention. For example, although the secondary imaging lens used in the focus detection device has been described in the above embodiments, the invention can be applied to an axially symmetric lens, a lens having a flat optical surface such as a mirror or a prism.

The same applies to the acrylic (PMMA) resin, and other optical resins (polycarbonate-based resin, olefin-based resin, norbornene-based resin, styrene-based resin, copolymers of these resins, blend-based resins, etc.). Can also be applied to.

[0028]

As described above, the following effects can be obtained by molding the optical element using the mirror surface piece manufactured by the fly-cut method according to the present invention. The gap between adjacent lenses of the compound lens can be processed to have an arbitrary size.

The parallelism and squareness of the lens to be molded can be guaranteed based on the performance of the machine tool. The number of parts of the mirror surface piece as a molding die member can be reduced,
The cost can be reduced. The ridge line positions of the lenses that are in contact with each other can be processed at any position.

With respect to the mirror surface property, the mirror surface piece can be uniformly processed, and the optical characteristics of the lens can be improved. Asymmetrical aspherical processing of the lens becomes possible. Only the effective use area of the lens can be processed,
As a result, the cutting area is reduced, which brings about an effect of extending the life of the tool as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a molded product of a secondary imaging lens used in the focus detection device of a camera according to the present embodiment.

FIG. 2 is a diagram showing a mirror surface piece for molding a secondary imaging lens used in the focus detection device for a camera according to the present embodiment.

FIG. 3 is a diagram showing a processing machine for the mirror surface piece shown in FIG. 2 and a processing state thereof.

FIG. 4 is a view showing a processing machine and a processing state of the mirror surface piece shown in FIG.

FIG. 5 is a view showing the external appearance of a tool for processing a mirror surface piece shown in this embodiment.

6 is a diagram showing a state of a lens transfer surface of a mirror surface piece processed by using the processing tool shown in FIG.

7 is a diagram showing a state of a lens transfer surface of a mirror surface piece processed by using the processing tool shown in FIG.

FIG. 8 is a diagram showing a processing procedure of the mirror surface piece of FIG. 2;

FIG. 9 is a diagram showing a molding method by injection molding of the secondary imaging lens of the embodiment according to the present invention.

FIG. 10 is a diagram showing a molding method by injection molding of the secondary imaging lens of the embodiment according to the present invention.

FIG. 11 is a diagram showing a molding method by compression molding of the secondary imaging lens of the embodiment according to the present invention.

FIG. 12 is a diagram showing a molding method by compression molding of the secondary imaging lens of the embodiment according to the present invention.

FIG. 13 is a diagram showing a molding method by compression molding of the secondary imaging lens of the embodiment according to the present invention.

FIG. 14 is a diagram showing a lens as a molded product of an example according to the present invention, which is a secondary imaging lens in the case where ridge lines are discontinuous.

FIG. 15 is a diagram showing a lens as a molded product of an example according to the present invention, which is a secondary imaging lens having an asymmetric aspherical shape.

FIG. 16 is a lens as a molded article of an example according to the present invention, in which 2 is obtained when only the effective use area is processed.
It is a figure which shows a secondary imaging lens.

FIG. 17 is a diagram illustrating a method based on a first conventional example.

FIG. 18 is a diagram illustrating a method based on a second conventional example.

FIG. 19 is a diagram illustrating a method based on a first conventional example.

FIG. 20 is a diagram illustrating a method based on a first conventional example.

FIG. 21 is a diagram showing a state of a lens transfer surface of a mirror surface piece processed by using a method based on a second conventional example.

FIG. 22 is a diagram showing a focus detection optical system for explaining the principle of focus detection.

FIG. 23 is a diagram showing a focus detection optical system for explaining the principle of focus detection when an error is included.

FIG. 24 is a diagram showing a secondary imaging lens when ridges are discontinuous.

FIG. 25 is a diagram showing a secondary imaging lens when the ridge lines are continuous.

[Explanation of symbols]

1 ... Secondary imaging lens, 2 ... NC lathe machine tool, 11 ... Lens part, 12 ... Lens part removal allowance, 13 ... Spindle, 14 ... Spindle rotation direction, 15 ... Mirror surface piece, 16 ... X-y axis movement Stand,
17 ... Diamond Bit, 18 ... Diamond Bit Tip, 20 ... Processing Line Width, 21 ... Continuous Cutting Cut,
22 ... Machining line moving direction, 23 ... Lens mirror surface piece, 24
... Frame piece, 25 ... Lens part, 26 ... Diamond tool for turning, 27 ... Grinding wheel for grinder, 29 ... Unprocessed part,
30 ... Lens effective use area, 31 ... Remains in the center,
32 ... Cutting marks for turning, 51 ... Injection mold, 52
... injection molding device, 53 ... injection unit, 54 ... mold clamping unit, 55 ... liner sprue, 56 ... compression molding die, 57 ... compression molding device, 58 ... compression molding blank,
59 ... Projection unit, C ... Gap between lenses, e ... Diamond tool turning radius, R ... Diamond tool cutting edge curvature radius, f ... Diamond tool cutting edge, g ...
Shank length, h ... Shank diameter

Claims (9)

[Claims] 1. By transferring the surface shape of an optical function surface of a molding die member onto a material of an optical element,
A method for molding an optical element, wherein a plurality of optical functional surfaces are transferred and formed on the same surface of the optical element, wherein the surface shape of the molding die member is such that a cutting edge of a diamond tool having a predetermined radius of curvature is directed toward an outer peripheral direction. A molding method of an optical element, characterized in that the tool is processed by engraving the molding die member by rotating the cutting tool, and molding is performed using the molding die member. 2. The radius of curvature of the cutting edge is approximately 3 mm or less,
The method for molding an optical element according to claim 1, wherein the circularity is set to about 1 micron or less, and the radius of rotation of the cutting edge is set to about 3 mm or less for rotation. 3. An optical element molded by the method for molding an optical element according to claim 1 or 2. 4. The optical element according to claim 3, wherein the optical element is a secondary imaging lens for a focus detection device mounted on a camera. 5. The optical element according to claim 4, wherein the plurality of optical function surfaces of the optical element are further formed by a plurality of lenses. 6. The optical element according to claim 5, wherein a ridgeline formed by contacting the plurality of lenses has a discontinuous shape. 7. The optical element according to claim 5, wherein all or some of the plurality of optical function surfaces of the optical element have an asymmetrical aspherical shape. 8. The optical element according to claim 5, wherein all or a part of the plurality of optical function surfaces of the optical element is composed of only an effective use area portion thereof. 9. The distance between a plurality of optical function surfaces of the optical element is set to 0.6 mm or less.
The optical element according to 1.