JPH02253223A - Single-lens reflex camera provided with focus detector - Google Patents

Abstract

PURPOSE:To prevent a shadow in a range-finding visual field from being caused at the time of observing by means of a finder and to detect a focus with high accuracy by specifying the optical arrangement of each element concerning a focus detecting means in an image deviation system and using a luminous flux passing through the primary image-formation surface of a finder system so that the focus may be detected. CONSTITUTION:The arrangement of each element of the focus detecting means is set to satisfy a formula (1), so that the luminous flux between the luminous fluxes m1 and m2 exiting from finder visual field ends 10b and 10c is effectively prevented from being made incident on other photodetector train 5-2 as unnecessary light by jumping over the optical axis L of a focus detection system after passing through a secondary lens 4-1 and having an adverse effect there. Provided that the image-forming magnification of a secondary optical system is taken as beta, a distance from the primary image-formation surface to the principal point on a front side of the secondary optical system is taken as X, the angle of a principal light beam from each center of the secondary optical system to the center of the viewing angle of the primary image-formation surface is taken as theta, the length of range-finding visual field on the primary image-formation surface is taken as (l) and the image height in the longitudinal direction of a photodetector train by the secondary optical system on the finder visual field end is taken as (h).

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a single-lens reflex camera having a focus detection device suitable for photographic cameras, video cameras, etc. The object image (finder image) is formed on the primary imaging plane in the finder system using the light flux passing through each area, and the light intensity distribution for the two object images is formed from the object image. The present invention relates to a single-lens reflex camera having a focus detection device that detects the in-focus state of an objective lens by determining the relative positional relationship between these two light amount distributions.

(Prior Art) Conventionally, there is a so-called image shift method as a light-receiving focus detection method that utilizes a light beam passing through an objective lens.

This image shift method is proposed, for example, in Japanese Patent Laid-Open No. 59-107311 and Japanese Patent Laid-open No. 59-107313, in which a field lens is placed near the expected imaging plane where the object image is formed by the objective lens. A secondary optical system having a porous mask and one or two secondary lenses is disposed behind the field lens, and a light receiving means having a plurality of light receiving element arrays is further disposed behind the field lens. ing.

Light fluxes from the field lens and the secondary optical system that have passed through two regions with different apertures of the objective lens are used to form light quantity distributions for the two subject images on the respective surfaces of the light-receiving element rows. At this time, the relative magnitude of the two light intensity distributions formed on the surface of the light-receiving element row is 1? The relationship, that is, the deviation of the light intensity distribution, differs depending on the focusing state of the objective lens6.For example, the lateral deviation in the direction of the alignment of the light-receiving element array-L according to the amount of defocus from the intended image forming plane of the objective lens. It appears in quantity.

The in-focus state of the objective lens, that is, the out-of-focus state, is 2 at this time.
This is done by detecting the relative positional relationship between the two light quantity distributions, that is, the amount of lateral deviation of the light quantity distributions using a light receiving means.

Generally, the relative lateral shift amount δ of the light quantity distribution on the two light-receiving element arrays at this time and the out-of-focus tied of the objective lens have a constant functional relationship.

In many cases, single-lens reflex cameras with an image shift type focus detection device are equipped with a focus detection device, as proposed in, for example, Japanese Patent Application Laid-Open No. 62-32409 and Japanese Utility Model Application No. 57-40919. It is placed at the bottom or on the pentaprism side. The light flux that has passed through the objective lens is guided to a focus detection device after passing through or being reflected by an eight-point mirror surface provided as a part of a quick return mirror.

(Problems to be Solved by the Invention) The method of arranging the submirror at the bottom of the camera requires that the submirror be placed behind the quick return mirror with high precision, and the parallax a! There were problems such as the need for l.

In addition, the method of placing the camera near the pentaprism above the camera separates the light flux for viewfinder observation and the light flux for focus detection using an eight-point mirror or the like near the primary imaging surface (focus plate) where the finder image is formed. ing. In this case, there is an advantage that unnecessary light fluxes from angles of view other than the light flux passing through the mirror do not enter the focus detection system and have no influence. However, since the light beam is divided near the primary imaging plane, the boundary of the division is observed, and the area near the center of the screen is clear <tU
There was a problem with being noticed.

On the other hand, if focus detection is performed without splitting the light beam near the primary imaging plane, unnecessary light beams from outside the range-finding field of view may overlap on the photodetector array, resulting in focus detection accuracy. There was a problem in that the value decreased.

The present invention achieves high precision by appropriately setting the optical arrangement of each element related to the focus detection device near the pentaprism above the camera, and by utilizing the light flux that has passed through the primary imaging plane (focus plate) of the finder system. The object of the present invention is to provide a partially reflex camera having a focus detection device that enables accurate focus detection.

(Means for Solving the Problems) The focus detection device according to the present invention forms a subject image by an objective lens near a primary image forming plane in a finder system, and A plurality of light intensity distributions regarding the subject image are generated from the subject image formed near the primary imaging plane using the light beams that have passed through different areas of the pupil of the objective lens by the secondary optical system disposed on the opposite side. is formed on a light receiving means surface consisting of a light receiving element array, the relative positional relationship of the plurality of light quantity distributions is determined by the light receiving means, and the in-focus state of the objective lens is determined using an output signal from the light receiving means. When calculating, the corresponding 2
The imaging magnification of the secondary optical system is β, the distance from the primary imaging plane to the front principal point of the secondary optical system is X, and the primary imaging plane from the center of each pupil of the secondary optical system is The angle of the chief ray to the center of the angle of view is θ
, the distance measurement field length on the primary imaging plane! , where h is the image height in the longitudinal direction of the light-receiving element array by the secondary optical system at the end of the viewfinder field of view... (1) It is characterized by satisfying the following condition.

(Embodiment) FIG. 1 is a schematic diagram of the main part of a first embodiment of the present invention, and FIG. 2 is a schematic diagram of a focus detection system extracted from FIG. 1 and expanded.

In FIGS. 1 and 2, 0 is a subject, 1 is an objective lens, and 9 is a quick return mirror.

Reference numeral 2 denotes a predetermined image forming plane of the objective lens l, which corresponds to the primary image forming plane, and a focus plate 10 is disposed near it.

Reference numeral 3 denotes a field lens, which is provided in a transparent area corresponding to the distance measurement area of the focusing plate 10, either integrally with the focusing plate 10 or independently. a is the field of view length for distance measurement, and is located near the field lens 3. Reference numeral 12 denotes a light splitter, and a half mirror surface 12a provided therein divides the incident light beam into two light beams: a light beam for viewfinder image observation and a light beam for focus detection.

Reference numeral 4 denotes a secondary optical system having an image-forming function and is constituted by two lenses 4-1.4-2 arranged symmetrically with respect to the optical axis of the objective lens l; 4-2
Two light-receiving element rows 5- arranged behind it corresponding to
1.5-2. The secondary optical system 4 establishes a conjugate relationship between the light receiving surface of the light receiving means 5 and the intended image forming surface. 6 is a diaphragm having two openings 6-1.6-2 arranged corresponding to the two lenses 4-1.4-2, and 7 is two divided regions 7-1.7-2. The exit pupils of the objective lens l configured by the following are shown. 11
is a calculating means, which calculates the relative positional relationship between the two, that is, the amount of deviation δ, from the light intensity distribution regarding the subject image from the two light receiving element arrays 5-1 and 5-2, and calculates the amount of defocus d of the objective lens. are doing.

Field lens 3, lens 4-1.4-2, aperture 6
-1, 6-2, etc. constitute a part of the optical means. still,
The field lens 3 has the function of forming an image of the aperture 6-1.6-2 near the area 7-1.7-2 of the exit pupil 7 of the objective lens l, and each area 7-1.7- The light beams transmitted through the light receiving element arrays 5-1 and 5-2 form a light amount distribution related to the subject image, respectively. P is a penta roof prism, E is an eyepiece, and F&I photosensitive surface.

In this embodiment, when the image forming point of the objective lens 1 is in front of the intended image forming surface 2, two light receiving element r rows 5-1.5
- 2, when the light intensity distributions of the subject images formed on each of the two light-receiving element arrays 5 become close to each other, and when the imaging point of the objective lens 1 is located behind the intended imaging plane 2, the two light-receiving element arrays 5
-1.5-2, the light amount distributions for the subject images formed on the respective surfaces are separated from each other.

At this time, the deviation amount δ of the light quantity distribution formed on the two light receiving element arrays 5-1, 5-2, respectively, has a certain functional relationship with the focal deviation ld of the objective lens l.

For this reason, in this embodiment, calculation is performed by defining an appropriate function by the calculation unit provided in the calculation means 11, and thereby the defocus Jld and the defocus direction of the objective lens l are determined.

At this time, in this embodiment, the optical arrangement of each element regarding the focus detection device is set as described above, and the condition (1) is satisfied. FIG. 3 is an explanatory diagram showing the optical arrangement of each element at this time.

m1 in the figure. m2 is the luminous flux m1.
The optical path of m2 is shown.

For example, X = 70 mm (air equivalent), θ = 2 degrees.

The settings are as follows: β=-Q, 33, j2=4mm%h=5.61mm.

In this embodiment, by setting each element so as to satisfy equation (1), the light flux m1. As shown in the figure, after passing through the secondary lens 4-1, the light beam between m2 passes through the optical axis of the focus detection system and enters the other light-receiving element array 5-2 as unnecessary light, thereby preventing it from having a negative effect. effectively prevented.

In other words, as shown in Figure 4, ha is located at the viewfinder field of view A.
Image points A', B by secondary optical system 4-1.4-2 of %B
Assuming that the distance (image height) from the sensor center 0°, 0゛° for ', A'', and C'' is 0''C, the condition that each sensor is not covered by the adjacent image is 0''C using the sign of each point in the figure. °Conflict B"E<0°E, where 0゛C゛・-"-1β! B"E-0"B"-0"E -h-(1◆1β I)
Xtanθ0°E −(1+1 β I)Xtan
Since θ, f, β14(h-(DI β1)Xtanθ)(t1
β I) Xtarl i.e. 21+l l Xtanθ −f) hI β l
2 1 β 1, and the above-mentioned equation (1) is obtained.

In this embodiment, the ratio of the day focus amount on the primary imaging plane (planned imaging plane 2) to the change in the distance between the subject images on the pair of light-receiving element arrays 5-1 and 5-2, that is, the sensitivity is approximately 1/21β1tan0443, that is, when the change in the distance between the two subject images formed on the two light-receiving element array surfaces is 1 μ, the amount of day focus change on the primary imaging plane is 43. .

In this embodiment, the secondary optical system 4 is configured to be separated from the primary imaging plane 2, and a light splitter 12 is shown in FIG. 1, which splits the light beam for the finder and the light beam for focus detection. It is placed between the pentaprism and the eyepiece, and its diopter is shifted from that of the viewfinder image to prevent shadows from forming on the viewfinder image.

(Effects of the Invention) According to the present invention, the optical arrangement of each element regarding the image shift type focus detection means is set as described above, and the focus is detected by using the light flux that has passed through the primary imaging plane of the finder system. By doing this, an optical member is installed near the primary imaging plane to separate the light flux for viewfinder observation and the light flux for focus detection, thereby limiting the range-finding field of view for focus detection. It is possible to achieve a single-lens reflex camera having a focus detection device capable of highly accurate focus detection without causing shadows in the distance measurement field during viewfinder observation.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of one embodiment of the present invention, and FIG.
Explanatory diagrams that extract and develop the focus detection system in Figures 3 and 4.
The figure is an explanatory view of a part of FIG. 2. In the figure, 1 is the objective lens, and 2 is the planned imaging plane (primary imaging plane).
, 3 is a field lens, 4 is a secondary to optical system, 5 is a light receiving means, 6 is an aperture, 7 is a lens, 9 is a quick return mirror, 11 is a calculation means, 10 is a focus plate, 12 is a light splitter, P
is a pentaprism, and E is an eyepiece.

Claims (2)

[Claims] (1) The object image formed by the objective lens is formed near the primary imaging plane in the finder system, and the pupil of the objective lens is formed by the secondary optical system placed on the opposite side of the objective lens of the primary imaging plane. A plurality of light intensity distributions regarding the subject image are formed on a light receiving means surface consisting of a light receiving element array from the subject image formed in the vicinity of the primary image forming plane using the light beams that have passed through different areas. When determining the relative positional relationship of a plurality of light quantity distributions by a light receiving means and determining the in-focus state of the objective lens using an output signal from the light receiving means, the imaging magnification of the secondary optical system is set to β, The distance from the primary imaging plane to the front principal point of the secondary optical system is X, and the angle of the principal ray from the center of each pupil of the secondary optical system to the center of the angle of view of the primary imaging plane Let θ be the length of the field of view for distance measurement on the primary imaging plane, l be the image height in the longitudinal direction of the light-receiving element array by the secondary optical system at the end of the viewfinder field, then [2(1+|β |)/|β|]・X・tanθ−l/
A single-lens reflex camera having a focus detection device that satisfies the following condition: 2>h/|β| (2) A focusing plate having a non-diffusive area is disposed within the distance measurement field of view near the primary imaging plane, and a field lens is provided integrally or independently in the non-diffusing area of the focusing plate. A single-lens reflex camera comprising the focus detection device according to claim 1.