JPH07119865B2 - Plastic lens mounting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a fixing structure for a plastic lens, and particularly when a compact structure and a position accuracy are required, such as a focus detection device for a camera, a change in temperature may occur. The present invention relates to a fixing structure for a plastic lens that does not deteriorate.

<Prior Art> Conventionally, various principles of a focus detection method for a camera are known. For example, in Japanese Patent Laid-Open No. 58-150918,
A method has been proposed in which two lenses are arranged at regular intervals and the intervals of images formed by the respective lenses are compared.

This principle will be explained with reference to FIG. 5 and FIG.
In the figure, 2 is a photographing lens, 6 is a condenser lens,
The portion on the right side of the condenser lens 6 is configured as one focus detection unit as shown by 8 in FIG. 6 and mounted on the camera. The primary image 28 of the subject formed by the taking lens 2 is formed by the pair of image forming lenses 10 and 12 arranged at a position serving as the exit pupil of the taking lens 2 with respect to the condenser lens 6. Two images 30, 32 (or 34, 36 or 38, 40) are formed by the light that has passed through different portions, and are re-imaged. Then, whether the primary image is imaged in front of the planned focal plane 22 (front pin), is imaged on the planned focal plane 22 (focused), or is imaged after the planned focal plane 22 ( The image interval between the re-imaging images 30, 32, etc., which changes depending on the focus state of the rear focus, is detected. A difference between the detected value and a reference image interval value which is an interval of re-imaging upon focusing (that is, an image interval deviation amount) is calculated, and based on the calculated value, the primary image 28 of the subject 28 taken by the taking lens 2 is calculated. The amount of deviation of the image formation position from the expected focus position (that is, the amount of focus deviation) can be obtained. Note that re-imaging is 30,3 in the figure when focused.
There are 2 positions, 34, 36 for the front pin, and for the rear pin
The positional relationship is 38,40. Hereinafter, such a focus detection method will be referred to as a phase difference method.

<Problems to be Solved by the Invention> Now, in this phase difference method, the focus detection unit 8 including the condenser lens 6, the pair of imaging lenses 10 and 12 and the photosensor array 42 is provided as shown in FIG. When the camera body of a flex camera (for example, the lower part of the mirror box) is to be incorporated, if the pair of imaging lenses are integrally molded with plastic, the optical focus detection section 8 can be configured in a compact unit, which is advantageous. is there. However, plastic generally has a linear expansion coefficient that is three to four orders of magnitude larger than glass (for example, the value is 6 × 10 ⁻⁵ / ° C. for acrylic resin), so when plastic is used for the optical part of the camera. The influence of the expansion and contraction of the plastic due to temperature change on the focus detection result cannot be ignored. In other words, in the case where the pair of imaging lenses are integrally molded of plastic, the distance between the two imaging lenses changes when the environmental temperature of the camera changes (for example, in a device having a size and shape as shown in FIG. 7, If the temperature rises 30 ° C, the lens spacing will be 2μ.
m increase). When this amount of change is viewed as the amount of focus shift of the imaging position of the photographing lens with respect to the planned focal plane 22, the amount of focus shift is as large as 68 μm, for example.

Here, the camera is usually used in a temperature range of −20 ° C. to + 40 ° C. or in a temperature range exceeding it. Further, a single-lens reflex camera is generally required to have a high focus detection accuracy of about ± 50 μm. In this regard, in Japanese Patent Application No. 59-91670, which is a prior application filed by the same applicant as the present applicant, it is premised that the distance between a pair of imaging lenses made of plastic and the temperature have a constant invariant relationship. As
The temperature sensor detects the temperature, calculates the amount of deviation of the imaging lens spacing from the reference value at that temperature, and performs a correction calculation in the data processing circuit to electrically influence the change due to thermal expansion of the lens spacing. I am proposing a correction method.

However, when actually trying to attach a plastic lens plate formed by integrally molding a pair of imaging lenses to the base of the focus detection unit, an adhesive was used to meet the demands for downsizing of the structure and improvement of productivity. In that case, it has become clear that the relationship between the distance between the imaging lenses and the temperature becomes complicated and unstable. In other words, this is because the shape of the plastic lens is regulated by the adhesive, so the reproducibility of the dimension of the lens spacing deteriorates when the temperature changes repeatedly,
This is considered to be due to complicated changes over time.

FIG. 9 shows the temperature change on the horizontal axis and the amount of deviation of the detected focus position of the focus detection device from the expected focus position (without correction by an electric circuit) on the vertical axis, and the dotted lines show a pair of imaging lenses. Is a simulation of the amount of shift due to temperature change when the device is supported without any restrictions. On the other hand, the solid line is the measured value when the plate pieces of the plastic lens integrally formed with the imaging lens are fixed to the base body by the adhesive A at both ends as shown in FIG. When the temperature is changed by one round trip, the deviation of the detection focus position of 24 μm from the result of the simulation remains. The correction calculation in the data processing circuit proposed in Japanese Patent Application No. 59-91670 is performed for the focal point shift indicated by the dotted line. Therefore, if the lens is fixed to the substrate with an adhesive, the dotted line The difference between the solid line and the solid line remains as an error in focus detection.

The present invention solves this problem, and in a focus detection device using a phase difference method, when a plastic lens integrally formed with a pair of imaging lenses is attached to the base of the optical detection unit, the temperature change as described above is performed. An object of the present invention is to provide a method of fixing a plastic lens, which eliminates the instability of focus detection accuracy due to the above, and effectively operates temperature compensation by a data processing circuit.

<Means for Solving the Problem> It should be noted in the present invention that, when a plate piece of a plastic lens integrally formed with a pair of imaging lenses is attached to the base body of the focus detection unit, the distance between the centers of both imaging lenses is increased. This is because we focused on ensuring the flexibility of expansion and contraction for the part. That is, in the focus detection method using the phase difference method, the distance between the centers of the pair of imaging lenses in the alignment direction particularly affects the focus detection accuracy. If the reproducibility of the lens is assured, the effect of temperature changes will appear as calculated based on the characteristics of the plastic lens, and therefore, for example, the detection image interval by the data processing circuit proposed by the applicant in the previous application is By using the correction means in combination, it is possible to perform focus detection with high accuracy.

In order to realize this, according to the present invention, the plate pieces of the plastic lens are not entirely fixed to the base in the same manner or the plate pieces are not completely fixed to the base body on both sides in the arrangement direction of the lenses. An attachment method of fixing the plate piece to the base body on a line segment orthogonal to was adopted. As a result, even when a temperature change occurs, the space between the centers of the two imaging lenses can be expanded and contracted almost freely with almost no restriction in the alignment direction of the two lenses. The reproducibility of the original characteristics was secured.

<Function> The plate piece of the plastic lens attached to the base body is 2
The plate piece is fixed to the base body on a perpendicular bisector connecting the centers of the two imaging lenses, and the plate piece freely expands and contracts due to the original characteristics of the plastic with respect to the temperature change with reference to this fixed portion. As a result, in the part between the centers of the two lenses, no unreasonable restriction is applied during expansion and contraction. Therefore, the influence of temperature change has a substantially constant relationship due to the original characteristics of the plastic lens, That is, it appears in the detection result of the image interval of re-imaging.

Further, according to the second aspect of the present invention, since the plate piece of the plastic lens is fixed to the base body at the three fitting portions of the boss and the boss hole on both sides of the lens, the plate piece of the plastic lens itself forms an image. The lenses are positioned with respect to the base body in the arrangement direction and the vertical direction, and the center distance between the two lenses expands and contracts almost freely in the arrangement direction.

<Embodiment> FIGS. 1, 2 and 3 show an embodiment in which the present invention is applied to the focus detection unit of the focus detection unit 8 in FIG. In FIG. 2, reference numeral 13 designates a base body in which a condenser lens 6 and a mirror for bending the optical axis at a right angle are incorporated. 14
Is a diaphragm plate having two vertically elongated openings 14a and 14b corresponding to the pair of plastic imaging lenses 10 and 12, respectively. The plastic imaging lenses 10 and 12 are integrally molded of acrylic resin, and are one plate piece 9 as a component. lens
On the vertical bisector of the line segment connecting the centers of 10, 12, boss holes h, h are respectively provided at positions close to both ends of the plate piece 9. Bosses B, B are formed on the side of the base body 13 corresponding to these boss holes, respectively.

To assemble, first, the holes 14c and 14d at both ends of the diaphragm plate 14 are passed through the bosses B and B, respectively, and then the boss holes h and h of the plate piece 9 are passed through B and B, respectively. When the diaphragm plate 14 and the plate piece 9 are overlapped and penetrated to the bosses B, B,
The tips of B and B have the same height as the surface of the plate piece 9 (the surface on the side visible in the figure). In this state, the adhesive A is applied between the tips of the two bosses and the surface of the plate piece 9. FIG. 1 is a sectional view showing the state of the boss, the plate piece and the adhesive at this time, but the plate piece 9 is the adhesive A at the upper end portion of the boss.
Since it is fixed to the base body 13 via the plastic plate piece 9, if there is a temperature change in this state, the plastic plate piece 9 can freely move in the arrow direction with reference to the two fitting portions of the boss holes h, h and the bosses B, B. It is possible to expand and contract, and therefore, the distance between the centers of the two lenses is in a state in which the degree of freedom of expansion and contraction due to temperature change is guaranteed in the arrangement direction.

At this time, it should be noted that it is important in the present invention to fix both sides of the lens in the smallest possible range on the above-described vertical bisector. The influence on the expansion and contraction in the direction can be minimized.

By the way, the adhesive A is of a type that is cured by ultraviolet irradiation, and it does not require heating for curing and has good workability. Generally, an adhesive having a linear expansion coefficient similar to that of the plastic of the lens material is desirable.
For example, a modified acrylic adhesive is suitable for lens materials such as acrylic resin and polycarbonate resin.

After the adhesive has hardened, the back cover 16 is attached to the substrate to complete the assembly. The photo sensor array 42 and the transparent cover 15 on the front surface thereof are attached to the back cover 16.

FIG. 3 shows a cross-section (when viewed from the side in FIG. 2) of a state in which the unit of the focus detection unit 8 is assembled,
It can be seen that the plate piece 9 is positioned and attached to the base body 13 in the optical axis direction and the vertical direction of the imaging lens.

FIG. 4 shows the effect of this embodiment. The simulation result (dotted line) described in the problem to be solved by the invention and the measured value (solid line) according to this embodiment are in good agreement, and the plate Compared to the result of FIG. 9 when both ends of one piece are directly adhered to the substrate with an adhesive, the shift of the detection focus position is 1 /
It is less than 3.

According to the above-described method of attaching the plastic lens, the expansion and contraction of the plastic lens plate piece is hardly regulated in the bonded portion by the adhesive (therefore, the plastic lens plate piece may be complicatedly deformed as the temperature change is repeated. However, in this structure, the adhesive wraps around between the plate piece 9 and the base body 13,
There is no problem that an adhesive layer is formed and the positions of the imaging lenses 10 and 12 in the optical axis direction are shifted from the design value by the thickness of the adhesive layer to cause an error in focus detection. Also,
At the time of assembly, the plate piece 9 can be easily positioned at a predetermined mounting position of the base body by the boss and the boss hole, which is effective in the assembling work.

FIG. 8 is a block diagram of a circuit for obtaining a signal indicating the amount of focus shift due to temperature change in the above embodiment.
Reference numeral 44 is an image interval detection circuit that detects the interval between the two images in FIG. 6 based on the signal output from the photosensor array 42, 46 is a temperature sensor that detects the ambient temperature, and 48 is the temperature sensor 46. It is an image interval correction amount output circuit that outputs an image interval correction amount signal according to temperature. Reference numeral 50 denotes an arithmetic circuit that corrects the image distance signal from the image distance detecting circuit 44 with a correction signal from the image distance correction amount output circuit 48, and outputs the corrected image distance signal, and 52 is the corrected image distance signal. It is a shift amount calculation circuit for calculating the focus shift amount based on the above.

In addition, the above-mentioned deviation amount correction is the ninth in Japanese Patent Application No. 59-91670.
The circuit configuration disclosed in the figure can also be adopted.

<Effect of the Invention> According to the configuration of the present invention, even when a temperature change occurs,
In the part between the centers of the two imaging lenses, there is almost no restriction in the direction in which the two lenses are lined up, and they can be expanded and contracted almost freely. As a result, the influence of the temperature change on the plastic lens appears almost as calculated based on the original characteristics of the plastic lens. Therefore, if a means for correcting the detected image interval in the data processing circuit is also used, it is possible to provide a focus detection device with high accuracy with respect to temperature changes.

Further, when the lens expands and contracts due to temperature change, the center portion of the imaging lens is not unduly regulated, so that the lens undergoes complex deformation during repeated expansion and contraction, which in turn deteriorates the accuracy of the focus detection device. There is no worry.

Further, according to the second aspect of the invention, since the plate piece of the plastic lens is fixed at the two fitting portions of the boss and the boss hole on the upper and lower sides of the lens, the plastic lens itself is arranged in the alignment direction of the imaging lens and It can be easily positioned at a predetermined mounting position with respect to the base body in the vertical direction, and the distance between the centers of the two imaging lenses can be expanded and contracted almost freely in the arrangement direction with respect to the temperature change.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of the present invention, FIG. 2 is an exploded perspective view of an embodiment of the present invention, FIG. 3 is a sectional view of a focus detection unit using the present invention, and FIG. 5 is a graph showing the effect of the example, FIG. 5 is an explanatory view of the optical configuration of the conventional example, FIG. 6 is a longitudinal side view of the same, FIG. 7 is a perspective view of the same optical system, and FIG. 8 is a block of a circuit in this embodiment. FIG. 9 is a graph for explaining the problem, and FIG. 10 is a front view showing an example of a plastic lens mounting structure for similarly explaining the problem.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G03B 13/36 (72) Inventor Katsuto Akagi 2-30 Azuchi-cho, Higashi-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. (56) Reference JP-A-58-150918 (JP, A) JP-A-57-64204 (JP, A) JP-A-57-105707 (JP, A)

Claims (3)

[Claims] 1. A focus having a transparent plastic plate piece integrally formed with at least a pair of imaging lenses used for focus detection by a phase difference method, the plate piece being attached to a predetermined position of a base body. In the detection device, the plate piece is fixed to the base body on a perpendicular bisector of a line segment connecting the centers of the pair of lenses, and both ends of the pair of lenses in the alignment direction are extendable in the alignment direction. A mounting structure for a plastic lens in a focus detection device characterized by the above. 2. Boss holes are provided through on the vertical bisector of a line segment connecting the centers of the pair of lenses and at two positions close to both side edges of the plate piece, and the base body is formed. Two plate bosses that fit into the two boss holes are provided in a protruding manner, and the plate pieces are attached to predetermined positions of the base by fitting the two bosses into the two boss holes, respectively. The plastic lens mounting structure according to claim 1. 3. The plastic according to claim 2, wherein the front ends of the two bosses fitted into the two boss holes and the surface of the plate piece are bonded to each other with an adhesive. Lens mounting structure.