JPS61165712A - Plastic lens fixing structure - Google Patents

Abstract

PURPOSE:To eliminate the instability of positional precision due to the variance of temperature by providing boss holes in both side edges in the direction orthogonal to the lens arrangement direction of a transparent plastic plate and inserting bosses on a base body to boss holes loosely and joining front end parts of bosses and the surface of the plastic plate with an adhesive. CONSTITUTION:Plastic focusing lenses 10 and 12 are formed as one body with an acrylic resin, and boss holes (h) and (h) are provided in both end parts on a perpendicular bisector of the segment connecting centers of lenses 10 and 12 of a plate piece 9. Bosses B and B are formed on a base body 13 in accordance with these boss holes. In case of assembling, holes 14c and 14d in both ends of a stop plate 14 are pierced by bosses B and B, and next, boss holes (h) and (h) of the plate piece 9 are pierced by bosses B and B. Bosses B and boss holes (h) are fitted loosely, and tips of bosses B and B are at the same height as the surface of the plate piece 9 when the stop plate 14 and the plate piece 9 are put one over the other and are pierced by bosses B and B. In such a state, an adhesive is applied to tips of bosses B and B and the surface of the plate piece 9. After the adhesive is hardened, a rear cover 16 is attached to the boss body, thus terminating assembling.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a fixing structure for plastic lenses, and is particularly useful in cases where a compact structure and positional accuracy are required, such as in a camera focus detection device. This invention relates to a fixing structure for plastic lenses that does not deteriorate.

Outline of the invention 8 Various principles have been proposed for focus detection methods, but
In a focus detection device that arranges two lenses at a constant interval and compares the images formed by each lens, when the two lenses are integrally made of plastic, plastic is generally 3 to 4 times smaller than glass. An order of magnitude larger linear expansion coefficient (for example, in the case of acrylic resin, 6X10/℃'
), the influence of thermal expansion cannot be ignored. In principle, it is possible to detect and compensate for the influence of this thermal expansion using an electric circuit that analyzes data on the image.

However, when plastic lenses are fixed using adhesive to meet the demands for smaller structures and improved productivity, the reproducibility of the lens spacing is poor due to repeated temperature changes, resulting in temperature compensation in data processing circuits. does not work effectively. This is thought to be because the shape of the plastic lens is regulated by the adhesive, and the adhesive undergoes complex changes over time due to repeated temperature changes. The present invention solves this problem by using an adhesive to fix the plastic lens so that it can expand and contract freely.

C. Prior Art FIG. 5 shows a camera focus detection device proposed in Japanese Patent Application Laid-Open No. 58-150918. In this figure, the imaging lens 10.
A problem arises when 12 is integrally molded from plastic. In this figure, 2 is a photographing lens, and 6 is a condensing lens.The part on the right side of the condensing lens 6 is constructed into a unit as shown by 8 in FIG. 7, and is attached to the camera.

By looking at FIG. 7, it will be understood that there is a strong demand for miniaturization of the focus detection device and that it is advantageous to integrate the imaging lenses 10 and 12 with plastic. The above conventional example will be explained below.

As shown in principle in FIG. 5, the device disclosed in Japanese Patent Application Laid-open No. 58-150918 separates the primary image 28 of the object formed by the photographic lens 2 from the exit pupil of the photographic lens 2 with respect to the condenser lens 6. A pair of imaging lenses 10 arranged at convenient positions
．． 12, two images 30.32 (or 34.36 or 38
．． 40), and whether the 1st and -th images are formed in front of the intended focal plane 22 (front focus) or on the intended focal plane 22 (in focus). Alternatively, the image interval between the re-imaging 30, 32, etc. that changes depending on the focusing state of the image formed after the predetermined focal plane 22 (rear bin) is detected, and this detected value and the time of focusing are calculated. The difference from the reference image interval, which is the re-imaging interval of The amount of shift, that is, the amount of focus shift is calculated. In addition, when re-imaging, the positional relationships are as shown in FIGS. 30 and 32 when in focus, the positional relationships are 34 and 36 when the front focus is on, and 38 and 40 when the rear focus is on. Hereinafter, for convenience, such a focus detection method will be referred to as a phase difference method. A condensing lens 6 and a pair of imaging lenses 10 for such phase difference detection.
12 and a photosensor array 42 is to be incorporated into the camera body of a single-lens reflex camera (for example, at the bottom of a mirror box) as shown in FIG. It is advantageous that the optical detection section can be formed into a compact module by integrally molding the optical detection section. However, plastic generally has a coefficient of linear expansion that is 3 to 4 orders of magnitude larger than that of glass (for example, in the case of acrylic resin, the value is 6 x 10-'/'C), so plastics are used in the optical parts of cameras. In this case, the influence of the temperature change of the plastic on the above focus detection results cannot be ignored. In other words, if the above pair of imaging lenses are integrally molded from plastic, the pair of imaging lenses will change as the environmental temperature of the camera changes. The distance between the lenses changes (for example, in a device with the dimensions and shape shown in FIG. 7, when the temperature rises by 30°C, the distance between the lenses increases by 2 μm). This amount of change is calculated as the expected focal point of the image forming position by the photographing lens 2. For example, when looking at the amount of defocus for position 22, it is 6.
This results in a large out-of-focus amount of 8 μm. Here, the camera is normally used in a temperature range of -20°C to +40°C or a temperature range exceeding that. Furthermore, a negative-eye reflex camera is generally required to have a high focus detection accuracy of about ±50 μm. For this reason, Junto Honde applied for a patent application in 1983-
No. 91670 detects the air temperature with a temperature sensor, calculates the deviation of the distance between the imaging lenses from a reference value, and performs a correction calculation in the data processing circuit to correct the influence of changes in the distance between the lenses due to thermal expansion. proposed an invention.

However, this proposal assumes that there is a constant relationship between the distance between the imaging lenses 10.12 and the temperature, whereas the plastic integral molding of the imaging lenses 10.12 is attached to the base with adhesive. It has become clear that the relationship between lens spacing and temperature when fixed is complex and unstable. In Figure 8, the horizontal axis shows the temperature change schedule, the vertical axis shows the amount of deviation of the detected focal position of the focus detection device from the expected focal position (without correction by the electric circuit), and the dotted line is the imaging lens. 10.12 is a simulation of the amount of deviation when it is freely supported, and the solid line is the actual measured value. In this actual measurement example, as shown in FIG.
If the temperature is changed back and forth from 30°C to 50°C, the detected focus position will shift by 24
A micrometer change remains, and the overall result deviates from the simulation result. Since the electric circuit corrects the shift in focus position shown by the dotted line, the difference between the dotted line and the solid line becomes an error in focus detection.

21 Problems to be Solved by the Invention The present invention attempts to solve the above-mentioned instability of position accuracy due to temperature changes when plastic lenses are fixed with adhesive.

E1 Means for solving the problem As shown in Fig. 1, boss holes are provided on both sides of the transparent plastic plate 9 in which two lenses are integrally formed in a direction perpendicular to the direction in which the lenses are arranged, and Boss B protruding from 13
was loosely inserted into the boss hole, and the tip of the boss B and the surface of the plastic plate 9 were bonded with adhesive.

A problem with a transparent plastic plate in which two lenses are integrally formed is the stability of the distance between the two lenses. In the present invention, since the plastic plate on which the lenses are formed is fixed to the boss via adhesive on both sides in the direction perpendicular to the direction in which the lenses are arranged, there is almost no restriction on expansion and contraction in the direction in which the lenses are arranged ( The plastic plate 9 is virtually equivalent to being held freely, and the deviation of the detection focus position is very close to the simulation result as shown in FIG.
The accuracy of temperature correction by the electric circuit is improved.

Effects According to the present invention, the plastic lens is held in a free state, no excessive force is applied to it due to thermal expansion, and there is no part where stress remains, so it is less affected by changes in humidity. appears as calculated with good reproducibility, so by using a correction method using an electric circuit, it is possible to achieve high accuracy (focus detection), and since no mechanical means such as screws are used to fix the lens, assembly work efficiency is improved. (The number of parts is also small, which is advantageous in terms of manufacturing.

FIG. 4 shows the effect of the embodiment described below, and the meaning of the figure is the same as that of FIG. 9. According to the present invention, the simulation results and actual measurements when the plastic lens is free I know that there is.

H. Embodiment FIGS. 2 and 3 show an embodiment in which the present invention is applied to the focus detection unit 8 in FIG. 6. In FIG. 2, reference numeral 13 denotes a base body, in which a condensing lens 6 and a mirror for bending the optical axis at right angles are incorporated. 14 is a diaphragm plate with two vertically long apertures 14a and 14b corresponding to the plastic lens 10.12.
has. The plastic imaging lens 10.12 is integrally molded from acrylic resin, and is a single plate piece 9 as a component. Boss holes h are transparently provided at both ends of the perpendicular bisector of the line segment connecting the centers of the lenses 10 and 12 of the plate piece 9. Bosses B, B are formed on the base body 13 side corresponding to the boss holes. To assemble, first insert the holes 14c and 14d at both ends of the aperture plate 14 into bosses B.

B, then insert the boss hole h of plate piece 9 into the boss B.

Pass through B. The fitting between the boss B and the boss hole is a loose fit, and when the aperture plate 14 and the plate piece 9 are stacked and the bosses B and B are penetrated, the tips of the bosses B and B touch the surface of the plate piece 9. It should be at the same height as (the side of the bond visible in the diagram). In this state, adhesive is applied between the tips of the bosses B and B and the surface of the plate piece 9. The adhesive used is a type that hardens when exposed to ultraviolet rays. This does not require heating for curing and has good workability. Generally, it is desirable that the adhesive has a coefficient of linear expansion comparable to that of the plastic lens material. 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 base 13 to complete the assembly. A photosensor array 42 and a transparent cover 15 on the front thereof are attached to the back cover 16.

Figure 3 shows a cross section of the assembled state, and the bosses B and B and the plastic lens plate 9 are connected with adhesive A only between the tip of the post and the surface of the plate 9. As explained in section 1, the freedom of expansion and contraction of the plate piece 9 in the direction in which the lines 1, 0, and 12 are arranged is guaranteed. Fig. 4 shows the effect of this example. The simulation results and actual measurements are in good agreement, and compared to the results shown in Fig. 8 when both edges were bonded directly to the substrate with adhesive. The deviation of the detection focus position is 1
/3 or less. In addition, in this structure, the adhesive wraps around between the plate piece 9 and the base 13, forming an adhesive layer, and the position of the lens 1.0.12 in the optical axis direction is shifted from the designed value by the thickness of this adhesive layer. The problem mentioned above does not occur.

FIG. 8 is a block diagram of a circuit for obtaining a signal indicating the amount of defocus in the above embodiment.

44 is an image distance detection circuit that detects the distance between the two images in FIG. 5 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 detected by the temperature sensor 46. an image distance correction amount output circuit that outputs an image distance correction amount signal according to temperature;
50 is a circuit 48 for transmitting the image interval signal from the image interval detection circuit 44;
52 is a calculation circuit that calculates the amount of focus deviation based on the corrected image spacing signal. Incidentally, in order to correct the amount of focus deviation due to temperature changes, it is also possible to employ the circuit configuration (FIG. 9) disclosed in the above-mentioned Japanese Patent Application No. 59-91670.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway perspective view explaining the present invention in detail;
Figure 3 is an exploded perspective view of an embodiment of the present invention, Figure 3 is a vertical sectional view of the main part of the same embodiment, Figure 4 is a graph explaining the effects of the embodiment, Figure 5 is an explanation of the optical configuration of a conventional example. Figures 6 and 6 are the same (longitudinal side view, Figure 7 is a perspective view of the optical system, Figure 8 is a block diagram of the circuit in the embodiment, Figure 9 is a graph explaining the problem, Figure 10 is the same). It is a front view of a conventional plastic lens adhesive structure. Agent: Hiroshi Agata, Patent Attorney Figure 3 Figure 4 PC Figure 5 Figure 6 Thread Figure 10

Claims (1)

[Claims] (1) A pair of lenses used in focus detectors, etc., where the two lenses are integrally formed from transparent plastic. Boss holes are provided close to both side edges of the plate piece, bosses corresponding to the boss holes are provided protruding from the base to which the plate piece is attached, the boss holes of the plate piece are inserted into the boss holes, and the boss holes are inserted into the boss holes. A plastic lens fixing structure characterized in that the tip of the hole and the surface of the plate piece are bonded.