JPS63139310A - Pattern projecting device for detecting focus - Google Patents

Abstract

PURPOSE:To execute an exact detection even in case of focal distance of an objective lens is varied, by projecting a pattern of a prescribed shape to the side of an object to be photographed, and measuring an image forming state of a projected pattern. CONSTITUTION:A field diaphragm 11 and a field lens are placed on a scheduled image forming surface of a photographic lens or its vicinity, and also, secondary image forming lenses 13a, 13b are provided so that optical axes become parallel. Luminous intensity distributions of these secondary images are photodetected by photosensor arrays 14a, 14b, respectively, and from a relative position relation of a pair of images, a focusing state of the photographic lens is detected. In this case, a pattern is formed to a striped pattern by which a space frequency falls successively, and the thinnest line width, width of a photosensor, a focal distance of a photographing optical system, and an optical magnification of a focus detecting device are denoted as Tmin, (a), (f), and beta, respectively. In this regard, when the photosensor array is placed in a scheduled image forming object, etc. of an objective lens, beta=1, and when in case of placing it in a secondary image forming surface, etc., its secondary image forming magnification is set as beta, a focus detection for satisfying an inequality I is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pattern projector preferably used for automatic focus detection in photographic cameras, cine cameras, video cameras, etc., and particularly relates to a pattern projector suitable for automatic focus detection in photographic cameras, cine cameras, video cameras, etc. The present invention relates to a pattern projector for automatic focus detection in which focus detection accuracy is improved in so-called passive automatic focus detection in which focus is detected by measurement.

[Conventional technology]

BACKGROUND ART Conventionally, two types of focus detection methods have been used in photographic cameras, cine cameras, video cameras, and the like.

One is the passive method proposed in, for example, Japanese Patent Application Laid-open No. 54-159259, and the other is the passive method proposed in, for example, Japanese Patent Application Laid-Open No.
This is an active method proposed in Publication No. 7-154206 and the like.

Among these, the active method is a method in which a light beam, such as an infrared light beam, is emitted from the camera side toward the subject, the light beam is scanned in synchronization with a light receiving element, and focus detection is performed by receiving the reflected light beam from the subject. It has the advantage of being able to perform focus detection with relatively high accuracy even when the subject is dark or when the contrast of the subject is low. However, when the subject is far away, the projected light beam may not reach a sufficient amount or the amount of reflected light from the subject side may not be sufficient, resulting in a decrease in focus detection accuracy.

The passive method detects the focus by detecting the imaging state of the subject image by the imaging system using a detection means installed in a part of the camera, and allows relatively high-precision focus detection even when the subject is far away. It has its advantages. However, when the subject side is dark or the contrast of the subject is low, it is difficult to detect the imaging state of the subject image well, resulting in a decrease in focus detection accuracy. A method is proposed, for example, in Japanese Patent Publication No. 49-19810.One of the techniques described in the publication is that a random pattern is projected from the camera side to the subject side using a light projection system, and a reflected pattern image from the subject is generated. The focus of the photographic lens is detected by detecting the It is starting to look like this.

Therefore, in the method using random patterns, both the pattern light emission and light reception are performed through the photographic lens, so-called full TT.
If you don't use the L method, things may get worse.

This is because when the focal length of the photographic lens changes, the distance measurement range of the pattern changes accordingly.
For example, when a telephoto lens with a long focal length is used, the pattern to be measured becomes uniform, making it difficult to detect the image formation state of the pattern.

On the other hand, the all-TTL method does not have the above-mentioned drawbacks, but instead requires a light projection system that projects the pattern to be installed inside the camera body, which results in an increase in the size of the camera and also reduces the light projection system inside the photographic lens. Ghosts occur due to multiple reflections of the light beam,
This causes deterioration of the optical performance of pattern images during light projection and light reception, and a deterioration of focus detection accuracy.

[Problem that the invention seeks to solve]

The purpose of the invention is to achieve good focus detection even when the object is dark or has low contrast, and in particular to achieve accurate focus detection even when the focal length of the objective lens placed in front of the focus detection device changes. The purpose is to provide a pattern form that makes it possible.

Then, a pattern of a predetermined shape is projected from the camera side to the subject side via the light projection system, and the focus of the photographing lens is adjusted by detecting the image formation state of the pattern projected on the subject side. is composed of a striped pattern in which the spatial frequency decreases sequentially, the narrowest line width is Tm1n, the width of the photosensor is a1, the focal length of the projection optical system is ',', the optical magnification of the focus detection means is β, however, the objective lens If the photosensor array is arranged at or near the planned image forming plane of , β = 1, and if it is arranged at the secondary image forming plane or near it, the secondary imaging magnification is β, then the following formula is written. Give.

Note that when a telephoto lens is attached to the camera body or when a zoom lens is set to the telephoto side, only the central part of the area projected onto the subject is received, so the projection pattern has a high spatial frequency in the central area. (It is preferable to configure the structure so that the frequency wavelength decreases toward the periphery.The projection pattern may be viewed as a line of black bands on a bright background, or as a line of bright bands on a dark background.) good.

〔Example〕

FIG. 1 schematically depicts a single-lens reflex camera with a built-in focus detection device equipped with a pattern projector. The pattern projector may be built into the camera body, but it is better to incorporate it into a part of the strobe device.

In the figure, l represents a light source, for example, an LED or the like. A condensing lens 2 condenses the light beam from the light source 1. Recently, LED devices with a focusing lens bonded to them are often used. 3 is a pattern chart in which a pattern having a shape to be described later is formed on a transparent plate, and 4 is a projection lens, which are arranged in this order.

5 is a subject, 6 is a photographic lens, and 7 is a detection device that detects the focusing state of the photographic lens by detecting the imaging state of the subject image. A driving circuit 8 causes the light source 1 to emit light based on a signal from the detection device 7.

Further, 9 is an optical path splitter such as a half mirror or quick return mirror, and 10 is an image receptor such as a silver halide film or a solid-state photographing element. As the detection device 7, for example, those having the configurations shown in FIGS. 5 to 7 can be used. The device shown in FIG. 5 has been proposed in Japanese Patent Application Laid-Open No. 155331/1983, so a detailed explanation will be omitted, but the device has a field diaphragm 11 and a field lens arranged on or in the vicinity of the expected image formation plane of the photographing lens. Furthermore, secondary imaging lenses 13a and 13b are provided so that their optical axes are parallel. With this optical arrangement, the pair of secondary images moves line-symmetrically according to the focus adjustment state of the photographing lens, so the light intensity distribution of these secondary images is received by photophotosensor arrays 14a and 14b, respectively. However, the focus adjustment state of the photographic lens can be detected from the relative positional relationship between the paired images. In the configuration shown in FIG. 6, an array 15 of lenslets is arranged on the intended imaging plane of the photographing lens,
Behind it is provided a sensor device 16 with a pair of sensor rows, in which the lens let array 1
5, the relative positional relationship between the pair of object images is detected. Furthermore, FIG. 7 shows a configuration that detects the focus adjustment state of the photographing lens based on the blur of the image, and the imaging optical path of the photographing lens is divided into two by a half mirror 17 and a mirror 18, and the planned image formation plane is used as the photo sensor array. It is optically sandwiched between 19a and 19b. The focal point is detected by comparing the degree of blurring of the images on the photosensor arrays 19a and 19b.

When photographing a subject with the camera shown in FIG. 1, lightly press the release button (not shown) to activate the detection device 7.
The focus adjustment state of the photographic lens 6 with respect to the subject 5 is detected. When the release button is further pressed, a drive mechanism (not shown) focuses the photographing lens 6 in response to an adjustment signal generated by the detection device 7, and the shutter is opened to expose the image receptor 10. However, when the subject has low brightness below a certain level or when the subject has low contrast, the detection device 7 determines that focus detection is difficult and inputs a signal to the drive means 8 to cause the auxiliary light to be emitted. The driving means 8 causes the light source 1 to emit light based on a signal from the detecting means 7 indicating that the auxiliary light should be emitted. Then, the pattern 3 is illuminated by the luminous flux emitted from the light source, and the pattern is projected onto the subject side by the projection lens 4. A reflected pattern image from the subject side 5 is guided by a photographing lens 6 to a detection device 7, and the detection device 7 detects the focus of the photographic lens 6 by detecting the imaging state of the formed pattern image.

FIGS. 2 to 4 are explanatory diagrams of one embodiment of the pattern. The stripe pattern in Figure 2 is pattern chart 3.
A figure in which the interval between lines extending in one direction from the center to both peripheries is constant, and only the thickness of the lines increases; the pattern in Figure 3 is a pattern in which the thickness of lines extending in one direction from the center to the peripheries is constant. and a figure in which the spacing between lines increases. The pattern shown in FIG. 4 consists of concentric circles whose line thickness is constant and the distance increases from the center to the periphery.The pattern shown in FIG.
In addition to 14b, these are also valid for a detection device comprising two further sets of photosensor arrays perpendicularly.

In this way, the shape of the pattern in this example is such that as you go from the center to the periphery, the thickness of the lines or the spacing between the lines becomes smaller (one of them becomes larger in turn. In other words, the spatial frequency of the pattern increases as you go from the center to the periphery). The configuration is such that the value decreases sequentially.

By configuring the pattern in this way, the characteristics of the pattern on the subject image formed by the photographic lens will not change and will always remain the same, no matter what focal length you use, from initial velocity lenses to wide-angle lenses. It is possible to measure distance using a uniform pattern.

For example, in FIG. 2, the pattern to be measured is range 21 when a telephoto lens is used, and range 22 when a wide angle lens is used. However, in both cases, the patterns to be measured have the same shape in which the spatial frequency gradually decreases from the center to the periphery. In this embodiment, by using such a pattern, excellent focus detection is always performed regardless of the focal length of the photographing lens.

However, when a wide-angle lens is attached, care must be taken not to make the pattern too fine on the photoelectric conversion element array of the focus detection device, otherwise focus detection accuracy may be impaired. For example, if a line thinner than the width of one pixel is formed on a pixel of the photosensor array, if the focus detection device uses a so-called blur detection method (Figure 7), even if the line is slightly blurred, it will not affect other pixels. If the focus detection device is of a so-called image shift type (Figures 5 and 6), even if there is a slight shift, the amount of shift cannot be detected as long as the line does not overlap other pixels. Therefore, it is conceivable that the focus detection accuracy will be lowered no matter which method is used.

Therefore, as shown in FIGS. 8 to 10, the minimum line width T m i
The following conditions are given to n.

However, a is the width of one pixel of the photosensor array, f is the focal length of the projection lens, and β is the optical magnification of the focus detection device. For example, β is 1 when a photosensor array is provided on the primary imaging plane, such as in a focus detection device using a blur detection method, and when a secondary imaging optical system is provided, the secondary imaging It becomes the magnification.

Generally, when detecting the focus state by pattern projection, the subject is dark and an auxiliary photography source such as a strobe is often used. This assumes a lens, and if the line width of the pattern is made thinner than the lower limit, the focus detection accuracy will be adversely affected if a 35 mm photographic lens is used. Note that the minimum line width of the pattern image formed on the planned image forming plane is
The ratio of the focal lengths of is the magnification and becomes T・(35/f), but the equation (1) above is based on the condition that the value multiplied by the magnification of the focus detection device is larger than the width of one pixel T・( 35/f)
・Derived from 1βlea.

Also, the focal length is 20 as the widest angle lens when using a strobe.
Assuming a lens of 'mm, the line width T satisfies the following conditions.
It is desired that the distance measurement field of view exists when using a 20 mm lens.

If this condition is not met, when a 20 mm lens is used, only a pattern with a line width less than the width of one pixel of the photoelectric conversion element array is produced, which deteriorates focus detection accuracy.

The minimum line width T min is as thin as possible if it satisfies the condition (1). When using a long-focal-length photographic lens, the metal body within the distance measuring field is a line with a blurred pattern. The maximum width of the center line is 100 m, which is the focal length of strobes.
In order to prevent the sharpness of the range-finding field of view from deteriorating when using a photographing lens of m, it is desirable that the following should be satisfied, where b is the range of the range-finding field of view on the intended imaging plane.

〔effect〕

According to the present invention, by specifying the shape of the pattern projected from the camera side to the subject side as described above, the shape of the pattern is determined to be within the distance measurement target range no matter what focal length of the photographic lens is used. can be kept almost constant, so
A light projection system for automatic focus detection that can always perform stable and highly accurate focus detection can be achieved.

Furthermore, according to the present invention, by specifying the shape of the pattern projected from the camera side to the subject side as described above, even when using a wide-angle photographic lens, the pattern for focus detection is always stable without being too small. A light projection system for automatic focus detection that is capable of highly accurate focus detection can be achieved.

[Brief explanation of the drawing]

FIG. 1 is an optical sectional view showing an embodiment of the present invention. FIG. 2, FIG. 3, and FIG. 4 are plan views of examples of projection patterns, respectively. FIG. 5 and FIG. 6 are sectional views of the focus detection device, respectively. FIG. 7 is a perspective view of the focus detection device. FIG. 8, FIG. 9, and FIG. 10 are plan views of projection patterns, respectively. In the figure, 1 is a pattern chart, 4 is a projection lens, 6 is a photographic lens, and 7 is a focus detection device.

Claims (1)

[Claims] A photo sensor array is arranged behind the objective lens to receive the light intensity distribution of the object image, and when forming a signal for focus adjustment, the projection optical system is used to direct the pattern toward the object. In a device for projecting images, the pattern is a striped pattern in which the spatial frequency sequentially decreases, the narrowest line width is Tmin, the width of the photosensor is a, the focal length of the projection optical system is f, and the optical distance of the focus detection means is The magnification is β, except that β if the photosensor array is placed at or near the intended imaging plane of the objective lens.
= 1, for focus detection that satisfies Tmin>(a・f)/(35・|β|), where β is the secondary imaging magnification when placed on or near the secondary imaging plane. pattern projection device.