JPH0522882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called TTL type focus detection device for detecting focus using an imaging light beam from a photographic lens, for example in a single-lens reflex camera.

A method that detects focus by receiving only reflected natural light from the subject is called a passive type. This passive type focus detection device works well when the subject brightness is bright enough, but when the subject brightness becomes darker than a certain value, the amount of light incident on the sensor is insufficient and the operation becomes unstable. becomes. In preparation for such a case, an auxiliary light source is installed in the camera body, and when the subject brightness is below the limit value, the auxiliary light source is emitted to illuminate the subject, and the subject brightness is sufficient for the focus detection device. It is also well known that the method of securing but,
There is no problem when using visible light as auxiliary light, but there is a big problem when using infrared light as auxiliary light. That is, it is difficult to realize a practical focusing optical system that is compatible with a focusing optical system that uses natural light for bright subjects and a focusing optical system that uses infrared light for dark subjects.

In general, in photographic lenses, there is a difference between the focus position for visible light and the focus position for infrared light, and it is not possible to take a well-focused photo unless you distinguish between visible light and infrared light and perform focus detection. . Conventionally known focus detection devices that detect focus by distinguishing visible light from infrared light have (1) two types of optical systems, one for visible light and one for infrared light. (2) A device that realizes focus detection for two types of light by inserting and removing an infrared cut filter into the focus detection device. In the former case (1), two types of optical systems must be prepared, and in the latter case (2), a mechanism for putting in and taking out the infrared cut filter is required, which is not practical.

An object of the present invention is to solve the above-mentioned problems and provide a focus detection device that can realize two types of focus detection, one for visible light and one for infrared light. The first and second
a field aperture, and a first field aperture near the first field aperture.
a first optical filter having a spectral transmittance characteristic different from the first spectral transmittance characteristic is provided in the vicinity of the second field aperture; A pupil dividing means and a secondary imaging optical system are arranged behind the image plane, and the first,
A first re-forming image formed by the objective lens near the second field aperture and corresponding to the image formed near the first and second field apertures at a position where these images are received; The present invention is characterized in that at least one pair of second photoelectric conversion element rows is provided.

The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 shows a first embodiment of the present invention, in which along the course of the light beam emitted from the photographic lens 1,
A light shielding member 2, an optical filter 3, a field lens 4, an aperture frame 5, a pupil divider 6, a secondary imaging lens 7, and a sensor board 8 are arranged in sequence near the intended image forming surface of the photographing lens 1. ing. Light shielding member 2
Two rectangular viewing apertures 2a and 2b are arranged in parallel, and an optical filter 3a having spectral transmittance characteristics that transmits only infrared light and blocks visible light is provided at the rear of the viewing aperture 2a. An optical filter 3b having a characteristic of transmitting only visible light and blocking infrared light is arranged at the rear of the viewing aperture 2b. Aperture frame 5
are provided with two rectangular aperture frames 5a and 5b, and wedge prisms 6a and 5b forming the pupil divider 6 are provided at the rear of these frames, respectively, and have different inclination angles from each other.
6b is placed. Further, the sensor board 8 includes a set of two line sensors 8a, 8b, 8c, 8d.
are arranged in two sets {8a, 8b} and {8c, 8d},
These sets are arranged parallel to the field apertures 2a, 2b.

Light ray L from the subject passing through the photographic lens 1
1, L2 is imaged at one point of the field aperture 2a, and only visible light reaches the field lens 4 by the action of the optical filter 3a, and the field lens 4 images the pupil of the photographing lens 1 near the pupil splitter 6. do. Therefore, the light ray L1 coming from one side of the pupil of the photographing lens 1
passes through the diaphragm frame 5a and enters the wedge prism 6a, where it is deflected upward where it has a large thickness and is imaged by the secondary imaging lens 7 on the line sensor 8a. Similarly, light ray L2 from the opposite pupil of photographic lens 1
is deflected downward by the wedge prism 6b and forms an image on the line sensor 8c. Secondary imaging lens 7
are set so that the image of the subject formed within the field aperture 2a is formed on the line sensors 8a, 8c of the sensor substrate 8, and the image of the field aperture 2b is formed on the line sensors 8b, 8d. In this way, one field aperture is formed on the sensor substrate 8 as two vertically separated images depending on the pupil position of the photographing lens 1. Therefore, the wedge prisms 6a and 6a are arranged so that the images of the two field apertures 2a and 2b do not overlap with each other.
If the apex angle of the field aperture 6b and the interval between the field apertures 2a and 2b are designed, a total of four field aperture images are formed on the sensor substrate 8 in parallel in the vertical direction. The line sensors 8a to 8d are installed corresponding to these four visual field images, and the visible light image formed on the visual field aperture 2a by the photographing lens 1 is formed by the field lens 4, the pupil splitter 6, and the secondary imaging lens 7. As a result, the image is re-imaged on the line sensors 8a and 8c.
Output signals from these line sensors 8a, 8c are supplied to a focus determination electric processing system, and by determining the amount of lateral shift on each line sensor 8a, 8c, focus detection for the visible light image can be performed.

On the other hand, when performing focus detection using infrared light as auxiliary light, the line sensor 8b , 8d, the infrared light image within the field aperture 2b is re-imaged. Therefore, by supplying the output signals from the line sensors 8b and 8d to the focus determination electric processing system, it becomes possible to detect the focus on the infrared light image.

In this way, in this embodiment, when the subject brightness is sufficiently bright, the line sensor 8a,
When the subject brightness is insufficient and the subject is illuminated with infrared light as auxiliary light, the output signals from line sensors 8b and 8d are
It is only necessary to provide each to the focus determination electric processing system.

FIG. 2 shows a second embodiment of the present invention, which differs from the first embodiment described above in that two field apertures 2a,
At this point, the distance between the prisms 2b becomes wider and the wedge angle of the wedge prisms 6a and 6b of the pupil divider 6 becomes smaller. In this embodiment, the image of the field aperture 2a is formed onto the line sensors 8a, 8b by the pupil splitter 6 and the secondary imaging lens 7, and the image of the field aperture 2b is similarly formed onto the line sensors 8c, 8d. imaged. Therefore, the visible light image is transmitted to the line sensors 8a and 8b.
The infrared light image is input as an electric signal to the focus determination electric processing system, and the infrared light image is supplied to the processing system via line sensors 8c and 8d, so that respective focus detections can be performed.

Compared to the first embodiment, the field aperture 2
Visible light, as the distance between a and 2b becomes wider,
Although it does have the disadvantage of having to detect focus on different parts of the subject when determining focus using infrared light,
On the other hand, the wedge prisms 6a, 6 of the pupil divider 6
Since the angle b is small, the aberrations of these prisms 6a and 6b are small, and there is an advantage that the re-formed image is less degraded.

FIG. 3 shows a third embodiment of the invention.
Compared to the first and second embodiments described above, the wedge prisms 6a and 6b of the pupil splitter 6 have different inclination directions, and the line sensors 8a to 8 of the sensor board 8 are different.
The arrangement of d is different. In this example,
Since the wedge directions of the prisms 6a and 6b of the pupil divider 6 are different from those in FIGS. 1 and 2, the arrangement of the images of the field apertures 2a and 2b formed on the sensor 8 plate is different. In Fig. 3, line sensors 8a, 8
b detects the visible light image, and line sensors 8c and 8d
detects an infrared light image, and is functionally similar to the first and second embodiments.

The fourth embodiment shown in FIG. 4 realizes the same function as the third embodiment by changing the configuration of the secondary imaging optical system. In this embodiment, the pupil splitter 6 consisting of wedge prisms 6a and 6b is omitted, and the secondary imaging lens 7 is composed of a pair of imaging lenses 7a and 7b having linear boundaries. It also serves as

FIG. 5 shows a fifth embodiment, in which the present invention is applied to an automatic focus detection optical system that operates effectively for a photographing lens 1 having a wide range of open F numbers. This embodiment basically has the configuration shown in FIG. 3, but the pupil divider 6 is divided into two parts: a deflector 6c for a bright F-number lens and a deflector 6d for a dark lens. Therefore, one visible light is divided into four field aperture images on the sensor substrate 8. Therefore, a total of eight field aperture images are obtained for the two field apertures 2a and 2b, and line sensors 8a to 8h are arranged corresponding to each field aperture image.
In this embodiment, line sensors 8a to 8h are used as shown in the following table.

Type of light image F-number of photographic lens used Line sensor Visible light bright 8a/8b Visible light dark 8c/8d Infrared light bright 8e/8f Infrared light dark 8g/8h In each of these cases, the line shown on the right side Based on the output signals of the sensor pair, the amount of lateral shift of the image is determined and focus determination can be performed.

As mentioned above, in general photographic lenses, the focus position for visible light and the focus position for infrared light are different. In order to make the focus detection device of the present invention work more effectively for strobe photography, etc., it is necessary to measure the difference in focus position between visible light and infrared light for each lens by measuring the length of the signal pin or the length of an electronic device such as a semiconductor memory. After reading this amount from the camera body and confirming in-focus using infrared light, move the photographing lens by the amount read and set the expected focus position using visible light. What is necessary is to have the camera body perform control such as positioning the photographing lens at , emitting strobe light, and taking a photograph.

In the present invention, since the visual field aperture 2a for visible light and the field aperture 2b for infrared light are slightly separated vertically, strictly speaking, the same part of the subject is photographed in the case of visible light and in the case of infrared light. However, if this interval is kept small, this will hardly be a problem in practice. Note that the optical filter 3 only needs to be placed near the light shielding member 2, and does not necessarily need to be placed immediately after it.

As explained above, in the focus detection device according to the present invention, the two field apertures, the visible light field aperture and the infrared light field aperture, are reimaged by a common secondary imaging optical system. , by using line sensors for visible light and infrared light, and simply switching the output signal supply from the line sensor to the focus judgment electric processing system, focus judgment can be made for either visible light or infrared light. is also possible.

[Brief explanation of the drawing]

The drawings show embodiments of the focus detection device according to the present invention, FIG. 1 is a block diagram of the first embodiment, FIG. 2 is a block diagram of the second embodiment, and FIG. 3 is a block diagram of the third embodiment. FIG. 4 is a block diagram of the fourth embodiment, and FIG. 5 is a block diagram of the fifth embodiment. Reference numeral 1 is a photographing lens, 2 is a light shielding member, 2a, 2
b is a field aperture, 3, 3a, 3b are optical filters,
4 is a field lens, 5, 5a, 5b is an aperture frame, 6 is a pupil divider, 6a, 6b is a wedge prism, 6c, 6d is a deflector, 7 is a secondary imaging lens,
8 is a sensor board, and 8a to 8h are line sensors.

Claims (1)

[Claims] 1. First and second field apertures are provided in the vicinity of the intended imaging plane of the objective lens, and a first optical filter having a first spectral transmittance characteristic is provided in the vicinity of the first field aperture. A second optical filter having a spectral transmittance characteristic different from the first spectral transmittance characteristic is provided near the second field aperture, and a pupil dividing means and a secondary image forming device are provided behind the predetermined image forming plane. An optical system is disposed in the vicinity of the first and second field apertures to re-image the images formed by the objective lens near the first and second field apertures, and to receive these images. A focus detection device comprising at least one pair of first and second photoelectric conversion element arrays each corresponding to an image to be formed. 2. The first and second field apertures are rectangular and arranged in parallel.
The focus detection device described in . 3. The first optical filter has a property of transmitting visible light and blocking infrared light, and the second optical filter has a property of blocking visible light and transmitting infrared light. The focus detection device according to the range 1 above.