JPH01120520A - Single-lens reflex camera equipped with focus detecting device - Google Patents

Abstract

PURPOSE:To detect a focus by providing a light splitting mirror, a submirror, an image re-forming lens and a photoelectric conversion means and arraying range finding visual fields set by image element rows only on a line in parallel with lines intersecting the planes of plural mirrors. CONSTITUTION:The splitting mirror 22 splits a portion of a luminous flux from a lens system to a finder system, and the submirror 26 reflects the luminous flux passing through the mirror 22 and leads it to a focus detecting device 27. A device 27 is provided with the image re-forming lens 51 which re-forms images of an object formed with the luminous flux reflected by the submirror 26 and forms secondary images, and a photoelectric conversion element train 55 forming plural image element rows. The range finding visual fields set by image element sets 60 and 62 are arrayed along the line intersecting the plane of the splitting mirror 22 and that of the submirror. By this constitution, electrical signals are read out as separate image element rows, and a focused state is operated as separate range finding visual fields. Algorithm for each signal processing is selected, and the camera can focus on an object.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus detection device, and more particularly to a device for detecting the focus adjustment state of an objective lens.

[Conventional technology]

It has become commonplace for photographic or video cameras to incorporate detection devices for automatic focusing. However, the distance measurement range is determined at the center of the viewfinder, and a camera that focuses on a subject at a desired position within the viewfinder screen has not yet been realized.

In other words, if the distance measurement field of view is set at the center of the screen, there will be no problem if the main part of the subject is located at the center of the screen, but if it is off the center of the screen, erroneous distance measurement will occur and the focus will be incorrect. There is an inconvenience that the photo will be blurry. In order to solve this problem, we measured the distance by shaking the camera horizontally and placing the main part of the subject in the center of the screen, then returned the direction of the camera while maintaining the current focus adjustment state, and then released the shutter. Although it is possible to perform a release operation, it is cumbersome and may not be possible if you are in a hurry. For example, it was difficult to respond to a request to take a photo in which a subject moving laterally was located off the center of the screen.

On the other hand, the imaging light flux from the objective lens is guided to a set of re-imaging lenses, the light intensity distribution formed by these lenses is received by the pixel array of the photoelectric conversion element, and the focus adjustment state of the objective lens is determined from the interval between both light intensity distributions. Devices for detection are well known.

One way to meet the requirement of measuring distance without shaking the camera toward objects located outside the center of the screen is to place another pixel row outside the pixel row placed on the optical axis. It is conceivable that the newly provided pixel row may receive a subject image that is off the center of the screen.

[Problems to be solved by the present invention]

However, in eye reflex cameras, it is common to place a sub-mirror behind the main mirror and guide the light beam reflected by the sub-mirror to the bottom of the mirror box and enter the focus detection device. In order to avoid interference between the mirror and the sub-mirror, it is necessary to control the size of the sub-mirror, and if the distance between the sub-mirror and the main mirror is increased, the distance between the planned equivalent plane of image formation and the focus detection device must become large. However, it was difficult to expand the range of the focus detection optical system.

The present invention aims to solve these difficulties. In order to achieve the purpose, a light splitting mirror that splits a part of the light flux of the objective lens to the finder system, a sub-mirror that reflects the light flux that has passed through the light splitting mirror out of the light flux, and a light flux reflected by the sub-mirror. a pair of re-imaging lenses that re-image an object image formed by a secondary image to form a secondary image, and a plurality of sets of pixel rows, for example, three or more, each receiving a light amount distribution regarding the secondary image, and a light amount distribution. A single-lens reflex camera is equipped with a photoelectric conversion means for converting a signal into an electrical signal, and the distance measurement field of view set by each set of pixel columns is a plane including the light splitting mirror and a plane including the submirror. By arranging them along a line parallel to the intersection line of , it was possible to increase the length of the distance measurement field of view.

〔Example〕

The focus detection device of the present invention can be used in single-lens reflex cameras that use silver halide film, -lens reflex electronic cameras, or video cameras, as well as in position detection devices for recording devices, processing machines, robot eyes, etc. .

FIG. 6 shows an example of the usage mode, and depicts the optical system of a -eye reflex camera, where 10 is a camera body and 20 is a detachable or replaceable lens barrel. 21 is an objective lens, and 1 is its optical axis. The optical axis 1 reaches a quick return mirror 22 with a semi-transparent region and is split into two parts. Along the inverted optical axis are a focusing screen 23, a pentaprism 24. An eyepiece lens 25 is provided to constitute a finder system for visual recognition.

A movable sub-mirror 26 and then a focus detection device 27 according to the present invention are arranged along the transmitted optical axis, and a driver (not shown) is operated by the output of the focus detection device 27, and the objective lens 2
1 position thread is adjusted. Incidentally, as is well known, the movable sub-mirror 26 is held by the quick return mirror 22.

A light source 28 such as an LED of an object illumination device illuminates a projection chart 29 on which a projection pattern is formed, and transmitted light is projected by a projection lens 30.

Hereinafter, the configuration of the focus detection device shown at 27 will be explained using FIGS. 1 to 3. FIG. 1 shows a perspective view, FIG. 2 shows a vertical cross-sectional shape, and FIG. 3 shows a positional relationship between a pixel row and a light amount distribution of a photoelectric conversion device consisting of a single chip. 42
is a multi-hole field mask, which in the figure has long sides in the horizontal direction and has rectangular apertures arranged in parallel; for example, the objective lens 21 in FIG.
is placed near the planned imaging plane. 43 is a filter that blocks light with wavelengths longer than near-infrared light. Reference numeral 50 denotes a split field lens, which is arranged slightly offset from the intended image formation plane of the objective lens. The divided field lens 50 includes lens parts 50a, 50b, 50c, 50d, which have different optical functions as described later.
50e, 50f-50g, and these parts are formed by changing either or both of the lens thickness and the radius of curvature of the lens surface. In addition, when each lens part is constructed separately, it can also be made of materials having different refractive indexes.

51 and 53 form a re-imaging lens unit with a two-hole diaphragm 52 in between, and the convex lens 51 converts the incident light into a state close to parallel light (the optical function is described in Japanese Patent Publication No. 33564/1983), Further, the two-image forming lens 53, which is made by joining two convex lenses 53a and 53b side by side, forms two secondary images of the object image formed by the objective lens. The aforementioned two-hole aperture 5
2 denotes vertically long elliptical openings 52a arranged in the horizontal direction in the drawing.
, 52b.

54 is a concave lens for field curvature correction, and is arranged on a transparent plastic package 56 that houses a photoelectric conversion device 55 (FIGS. 2 and 3).

In addition, the split field lens 50. The convex lens 51 and concave lens 54 of the re-imaging lens unit are shaped vertically, but both are rotationally symmetrical spherical lens systems.

The light beams passing through the apertures 42...42g of the multi-hole field mask 42 are directed to the lens portions 50a-50b, 50c of the split field lens 50, as shown in FIG.

50d, 50e, 50f and 50g, and form secondary images of the object on the photoelectric conversion device, respectively. Figure 3 shows this situation, with 60a and 60b, -60m
and 60n, and 62a and 62b are a set of pixel rows consisting of a large number of pixels, and a filter having a bandpass characteristic approximately equal to the emission wavelength of an object illumination device to be described later is formed on 62a and 62b. Images 6 of the apertures 42a...42g of the multi-hole field mask correspond to these pixel columns.
1a...61n are projected, and a secondary image of the object is formed inside this. At that time, the mask 42 and the device 55 are adjusted according to the width of each aperture of the multi-hole viewing mask 42, the width of the light shielding zone 42h...42m between each aperture, the width of the pixel row on the photoelectric conversion device 55, and the pitch of the pixel row. Since the refractive power of the optical system that relays the image, especially each lens part of the split field lens and the re-imaging lens unit, is adjusted, the light-shielding bands 42h...42m of the multi-hole field mask each emit a predetermined aperture. Part of the light flux is prevented from entering pixel columns other than the pixel column corresponding one-to-one with this aperture. In addition, the field mask image includes the aperture apertures 52a, 52b and the lens portion 53.
a and 53b, two images are formed in parallel in the lateral direction for each aperture of the multi-hole field mask 42, and the secondary images of the object inside are formed as shown by the arrows in relation to the position of the object image with respect to the intended imaging plane. Move in direction A and direction B. therefore,
Since each set of pixel columns detects the relative interval of the light amount distribution regarding the pair of secondary images based on the photoelectric conversion output, it is possible to know the focus state of the objective lens for a plurality of distance measurement positions.

In addition, the pixel row is shaped to match the distortion of the visual field mask image,
It is desirable that the moving direction of the secondary image and the pixel column direction be configured to completely match. Further, each pixel column is separated to form a set, but a set may be created by allocating two ranges of one pixel column.

Next, the effects of the divided field lens according to the present invention will be explained using FIGS. 4 and 5. In Figure 4, a point T in the distance measurement field on the optical axis on the planned image formation plane (Figure 2) and a point U in the distance measurement field off the optical axis are photoelectrically converted through field mask apertures 42d and 42g. 70 in the figure shows how it is projected onto the element.
71 is a ray of light emitted from point T, and 71 is a ray of light emitted from point U.

As shown in FIG. 2, the light ray 70 is transmitted through the central lens portion 50d of the field lens, while the light ray 71 is transmitted through the peripheral lens portions 50f and 50g. At this time,
These two lens parts are configured to align the image formation state on the photoelectric conversion device, and qualitatively, by increasing the lens thickness of 50f and 50g, which point is the image formation point of point 19 U? Points V and W also located on the photoelectric conversion device
becomes. As a result, it becomes possible to maintain uniformly high focus detection accuracy in each distance measurement field of view.

FIG. 5 shows an image obtained by back projecting the two apertures 52a and 52b of the diaphragm 52 onto the exit pupil of the objective lens through the endmost aperture 42a of the multi-hole field mask and the field mask aperture 42d on the optical axis. , 80a.

81a, 80b, and 81b are aperture apertures 52a, respectively.
, 52b (Fig. 1), and 80a, 81
b is the image passing through the field mask aperture 42d, 81a,
8 lb is the light that has passed through the field mask aperture 42a. As can be seen from the figure, by optimizing the field lens for each distance measurement field of view, it is possible to create a configuration in which the focus detection light beam is not eclipsed at any distance measurement field position. As a result, the distance measurement field of view position is not limited to the vicinity of optical axis 1 (
This allows for a wide range of settings.

Incidentally, the light directed to the joint portions 50h to 50g of the field lens is through the light-shielding bands 42h and 42i of the field mask.

The light is blocked by 42f and 42m to prevent the generation of ghost light due to light incident on these parts.

Further, although the illustrated split field lens is made by integral molding of plastic, it is also possible to form each lens part individually and then combine them.

FIG. 7 shows the arrangement of the distance measurement field of view, and in accordance with the single-lens reflex camera shown in FIG.
1a...91g and 92 are laid out in parallel.

And the set of pixel columns 60a, 60b...60m in FIG.
・If 60n is back-projected onto the intended imaging plane using the re-imaging lens unit, and the distance measurement field of the focusing screen 23 is replaced on the intended imaging plane, the set of pixel rows and the distance measurement field will overlap, respectively. Become. This is a direction in which the arrangement direction of the set of pixel columns coincides with the intersecting direction of the plane including the camera body sub-mirror 26 (perpendicular to the drawing).

Adopting this arrangement has the advantage that the range from the distance measurement field of view at one end to the distance measurement field of view at the other end can be maximized without increasing the width of the movable submirror in the vertical direction.

The horizontal stripe pattern in FIG. 8 shows an example of a projection pattern projected onto an object with low contrast or low brightness.
This is depicted in chart 29 of FIG. Assuming that this figure is a projected pattern image projected onto an object, reference numeral 93 indicates the distance measurement range when the set of pixel columns 62a and 62b in FIG. 3 is back-projected onto the object. As mentioned above, the pixel rows 62a and 6
A bandpass filter having a wavelength substantially equal to the emission wavelength of the illumination light source 28 (FIG. 6) is formed on 2b, and the pixel array selects and senses the projected pattern reflected by the object. This forcibly adds contrast to objects that are normally difficult to detect, and enables focus detection using the pixel rows 62a and 62b. By the way, 94 is a pixel row of 60g/62h
This is the distance measurement range on the object.

With the above configuration, the electrical signal from the photoelectric conversion device 56 (FIG. 1, etc.) is read out for each pixel column, and, for example, the in-focus state is calculated for each distance measurement field of view, and the continuity is verified. Various signal processing algorithms can be selected, such as selecting a nearby object within a highly continuous range, or selecting a predetermined distance measurement field of view in advance and focusing on an object that has entered that field.

〔Effect of the invention〕

According to the present invention described above, since the distance measurement field of view can be made long, it is possible to carry out distance measurement at a large number of points within a wide range. Furthermore, it is possible to continuously perform focus detection on a moving object while keeping the direction of the camera fixed.

Moreover, since the pixel row direction is orthogonal to the direction in which the distance measurement fields of view are arranged, even if a photoelectric conversion device that requires charge accumulation such as COD is used, the movement of the object in the direction of the distance measurement fields of view This has the advantage that there is no low contrast ratio of the image signal and accurate focus detection is possible. Furthermore, there is also the effect that by aligning one pixel column of the photoelectric conversion device with respect to the re-imaging lens, the other pixel columns will also be at appropriate positions.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention. FIG. 2 is an optical cross-sectional view. FIG. 3 is a front view of the photoelectric conversion device. FIG. 4 is an optical partial cross-sectional view. FIG. 5 is a perspective view. FIG. 6 is a sectional view of a configuration showing an example of application to a camera. Figure 17 is a plan view of the observation field. FIG. 8 is a diagram showing the relationship between a projection pattern and a pixel column. In the figure, 42 is a multi-hole field mask, 50 is a split field lens, 50a...50g are lens parts, 51 is a convex lens of a re-imaging lens unit, 53 is a two-image forming lens, 52 is a two-hole aperture, and 55 is a photoelectric conversion Device, 60a/Son
, 62a, 62b are pixel columns.

Claims (1)

[Scope of Claims] A light splitting mirror that splits a part of the light flux of the objective lens to the finder system, a submirror that reflects the light flux that has passed through the light splitting mirror out of the light flux, and the light flux reflected by the submirror is formed. a pair of re-imaging lenses that re-image an object image to form a secondary image, and a plurality of sets of pixel columns each receiving a light intensity distribution regarding the secondary image, and converting the light intensity distribution into an electrical signal. and photoelectric conversion means for converting, the distance measurement field of view set by each set of pixel columns is along only a line parallel to the intersection of the plane containing the light splitting mirror and the plane containing the sub-mirror. A single-lens reflex camera equipped with a focus detection device characterized in that the focus detection device is arranged in a single-lens reflex camera.