JPH083577B2 - Optical system for focus detection - Google Patents

Description

The present invention relates to an optical system for focus detection of an automatic focus detection device using an image phase difference method.

[Conventional technology]

An image formed by the objective lens is divided into two by the re-imaging optical system and re-formed on the photoelectric conversion element array, and focus detection is performed by detecting the position shift between the two images. Many optical systems have been conventionally proposed. A typical example thereof is that shown in FIG. 9, which is composed of a condenser lens 3 located near the image plane 2 of the objective lens 1 and a pair of re-imaging lenses 4. The in-focus point is detected by the relative positional deviation between the pair of images formed on the conversion element array 5. In this type, the accuracy of focus detection is directly affected when the position of the image on the photoelectric conversion element array 5 is deviated due to an error in the mounting of the optical system or the like, so that the mounting accuracy is very severe. Further, when the optical system is mounted in the camera body, it is necessary to add one or two reflecting surfaces due to size restrictions.
That is, it is an indispensable condition to mount at least three or more optical members with high accuracy, and there is a drawback that adjustment between the optical members including the photoelectric conversion element array 5 increases.

[Problems to be solved by the invention]

In view of the above problems, it is an object of the present invention to provide a focus detection optical system that enables highly accurate focus detection while reducing the number of optical members as much as possible.

[Means and Actions for Solving Problems]

The focus detection optical system according to the present invention includes a condenser lens located near the image forming surface of the objective lens, and a pair of re-imaging lenses that re-image the image formed by the objective lens on the photoelectric conversion element array. In the optical system for focus detection consisting of, the condenser lens is formed on the incident surface, and the pair of re-imaging lenses is formed on the exit surface to form an integral optical member.

 This will be specifically described below.

As is well known, the condenser lens located near the planned focal plane of the objective lens plays a role of projecting the exit pupil of the objective lens onto the pair of re-imaging lenses. Further, the pair of re-imaging lenses re-forms the image of the objective lens on the rear photoelectric conversion element array.

By forming a condenser lens on the entrance surface and forming a pair of re-imaging lenses on the exit surface to form an integral optical member, the objective lens 1 and the optical element 6 as shown in FIG. The optical function equivalent to that of the optical system is obtained. In other words, the necessary requirement for each lens is the refractive power, which is realized in the form of a refractive surface having a curvature. With this configuration, the following advantages can be obtained.

First, since it is integrally molded with a plastic optical material or the like, alignment of the relative position between the optical axis of the condenser lens and the re-imaging lens is completely unnecessary if the parts are accurately prepared. . This is simpler and more reliable than the case where the relative positions of a plurality of optical members are determined with high accuracy. Secondly, even if a reflecting surface is provided between the optical systems, no reflecting mirror is required. For example, in the case of PMMA (polymethylmethacrylate), the critical angle is about 42 ° 5 ', and other plastic optical materials usually have total internal reflection at an incident angle of 45 °.
That is, when the optical path is bent 90 °, it is sufficient to form a slope having an inclination angle of 45 °, so that the reflecting mirror member required in the conventional example is unnecessary. If total reflection is not perfect due to the convergence and divergence of the light, the slope may be plated with silver.

Further, the condenser lens needs to have a function of correcting the aberration generated in the re-imaging lens, but for that purpose, it is necessary to make the curved surface corresponding to the condenser lens an aspherical surface to reduce distortion and field curvature. Further, by adding a convex lens to the condenser lens section, sufficient performance can be guaranteed. This convex lens can be a plano-convex lens with a flat surface facing the object side. That is, the condenser lens can be composed of a concave air lens.

As described above, the number of optical members can be made extremely smaller than in the conventional case, the structure can be simplified and high reliability can be achieved, and the cost reduction can be realized by reducing the number of parts and the number of assembling steps.

Further, the luminous flux necessary for focus detection is from a limited aperture in the arrangement direction of the photoelectric conversion elements, and correspondingly, a rectangular light shielding member is usually provided in the condenser lens portion and a re-imaging lens portion. A light shielding member having a pair of openings is provided to regulate the luminous flux. However, according to the present invention, it is easy to form the condenser lens portion and the re-imaging lens portion in a form corresponding to the above-mentioned aperture, and it is possible to give the refracting power only to the effective light beam, which is effective. Further, even when the light shielding member is further provided, it is only necessary to fit the opening having a shape corresponding to the lens, and the positioning of the opening of the light shielding member can be performed extremely accurately and easily as compared with the conventional example.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.

FIG. 2 shows the structure of the first embodiment, in which a condenser lens portion 8, a reflecting surface 9 and a pair of re-imaging lens portions 10 are integrally formed. The light flux is totally reflected by the reflecting surface 9. Reference numeral 7 is a focal plane of the objective lens, and 11 is a photoelectric conversion element array.

FIG. 3 shows the structure of the second embodiment, which includes the rear surface 14, the reflecting surface 9, and the pair of re-imaging lens parts 10 of the condenser lens part.
Are integrally formed, and a convex lens 12 is further added to the condenser lens portion to form an air lens 13.

FIG. 4 shows the structure of the main part of the third embodiment. The basic structure of the entire optical system is the same as that of the first embodiment, but the condenser lens is arranged in accordance with the area through which the light flux effective for focus detection passes. The shapes of the part 15 and the pair of re-imaging lens parts 17 are determined. The condenser lens portion 15 has a shape elongated in the arrangement direction of the photoelectric conversion elements as shown in FIG. 5, and the light shielding member 16 'added thereto has a shape as shown in FIG. The opening 15 'corresponds to the condenser lens portion 15. The flat portion 16 is a contact surface of the light shielding member 16 '. Similarly, the pair of re-imaging lens units 17, as shown in FIG.
The light shielding member 18 'formed in the arrangement direction of the photoelectric conversion elements and added thereto has a shape as shown in FIG. 9, and its opening 17' corresponds to the re-imaging lens unit 17. Flat part
Reference numeral 18 is a contact surface of the light shielding member 18 '.

〔The invention's effect〕

As described above, the focus detection optical system according to the present invention is formed as an integrated optical member by forming the condenser lens on the entrance surface and the pair of re-imaging lenses on the exit surface. It eliminates the need for high-precision adjustment between members, and the number of optical members can be made extremely smaller than in the past, and simplification of the configuration and high reliability can be achieved. There is an advantage that cost reduction is realized by reduction.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a focus detection optical system according to the present invention, and FIG.
FIG. 3 and FIG. 3 are sectional views showing the structures of the first and second embodiments, respectively, FIG. 4 is a sectional view showing the structure of the third embodiment, and FIGS. 5 and 6 are respectively the third embodiment. A perspective view of the condenser lens unit and a plan view of a light shielding member of the condenser lens unit. FIGS. 7 and 8 are perspective views of a pair of re-imaging lens units and a re-imaging lens unit of the third embodiment, respectively. FIG. 9 is a plan view of the light shielding member, and FIG. 9 is a sectional view showing the structure of a conventional example. 1 ... Objective lens, 2 ... Image plane, 5 ... Photoelectric conversion element array, 6 ... Optical element, 7 ... Focal plane, 8 ... Condenser lens section, 9 ... Reflection surface, 10 ... Re Imaging lens unit, 11
...... Photoelectric conversion element array, 12 ...... Convex lens, 13 ...... Air lens, 14 ...... Condenser lens part rear surface, 15 ...... Condenser lens part, 15 '...... Aperture, 16 ...... Flat surface part, 16' ...
… Shading member, 17 …… Re-imaging lens part, 17 ’…… Aperture, 18
...... Flat part, 18 '…… Shade member.

Claims (2)

[Claims] 1. A focus detecting device comprising a condenser lens located near the image plane of an objective lens and a pair of re-imaging lenses for re-imaging an image formed by the objective lens on a photoelectric conversion element array. In the optical system, the focus detecting optical system is characterized in that the condenser lens is formed on an entrance surface and the pair of re-imaging lenses are formed on an exit surface to form an integral optical member. 2. The focus detecting optical system according to claim 1, wherein the condenser lens is constituted by a boundary having a curvature, an air lens, or an optical system including an air lens.