JPH0548454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called TTL type focus detection device that can be effectively used in single-lens reflex cameras and the like.

FIG. 1 is a block diagram of a focus detection optical system using a secondary imaging method that the applicant has already proposed.
, a distance measuring field mask 4 having a slit 3 , a field lens 5 , and a first triangular prism mirror 6 for deflecting the optical path are arranged in sequence along the optical path of the imaging light flux that passes through the sub-mirror 2 and is reflected downward by the sub-mirror 2 . A sensor board having a diaphragm 7 having an aperture of 11 are arranged. The field mask 4 is located near the planned image plane, and the pupil of the photographing lens 1 is imaged near the diaphragm 7 by the field lens 5, and the two apertures of the diaphragm 7 are slightly smaller than the pupil image. It is becoming. The light flux passing through the field lens 5 is the first
It is reflected by the metal reflective surface 12 of the second triangular prism mirror 6, is deflected, travels through the secondary imaging lenses 8a and 8b as light beams a and b, and is further reflected by the reflective surface 13 of the second triangular prism mirror 9. , first, second
images are formed on line sensors 10a and 10b, respectively. And these two line sensors 10a, 1
The in-focus state is determined based on the degree of correlation between the output image signals from 0b.

However, in this focus detection optical system, a long line sensor is required so that the two line sensors 10a and 10b are in a straight line.
It becomes expensive in terms of cost. Moreover, the space in the longitudinal direction of the line sensors 10a, 10b becomes large, which becomes an obstacle to miniaturization of the optical system.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and provide a focus detection device that can downsize a line sensor and is advantageous in terms of cost. A field lens is provided near the surface, the pupil image of the objective lens is imaged near a single secondary imaging lens provided behind the field lens, and a line sensor is provided on the image side of the secondary imaging lens. are arranged in two rows in parallel, means for dividing the image formed by the objective lens into two images is provided in front of the planned image forming plane, and optical apertures are arranged in parallel corresponding to these two divided images. and means for shifting the divided light beams in the longitudinal direction of the line sensor closer to the intended image forming plane between the intended image forming plane and the secondary imaging lens; and the image shift direction are directions perpendicular to each other, and the focus determination is performed based on the output signal of the line sensor.

Next, the present invention will be explained in detail based on the embodiments shown in FIG. 2 and below. Here, the same reference numerals as in FIG. 1 indicate the same members.

In FIG. 2, the image dividing means forms a one-dimensional microprism on the entrance surface 20, sequentially along the optical path of the imaging light flux that has passed through the photographic lens 1 and been reflected downward by the sub-mirror 2, and a light splitter 22 having two different slopes on the surface 21; slits 23a arranged in the vicinity of the imaging plane of the photographing lens 1 and arranged in two rows parallel to the direction of the marking lines of the microprism; 23b, and prisms 25a and 25b having inclined surfaces in opposite directions to shift the luminous fluxes a and b divided by the light splitter 22 in a direction orthogonal to the division direction. Prism 25a, 2
Field lens 26 integrally formed with 5b
and are arranged. And further along the optical path,
A first triangular prism mirror 6 for deflecting the optical path, a diaphragm 27 having one aperture, and one secondary imaging lens 28 for forming the images in the slits 21a and 21b, A second triangular prism mirror 9 that deflects and first and second line sensors 29a and 29b arranged in two rows in parallel are provided.

Fig. 3 is a developed diagram for explaining the progress of light seen from the direction in which the luminous flux is divided into luminous fluxes a and b, and Fig. 4 is a developed diagram showing the direction in which the divided luminous fluxes a and b are shifted, that is, the direction in which the luminous flux is divided into luminous fluxes a and b. It is a developed view seen from the orthogonal direction.

The imaging light beam from the photographic lens 1 is transmitted to the light splitter 22
As shown in FIG. 3, two light beams a,
At the same time, the traveling directions of the respective light beams a and b are deflected. The two divided light beams a and b are deflected again at the exit surface 21 of the splitter 22, and are emitted in the same direction as the incident light beam. 2 made in this way
Slits 23a, 23b are located at positions corresponding to the two images.
A distance measuring field mask 24 is disposed, and the image light beams a and b passing through this field mask 24 are shifted by prisms 25a and 25b in a direction perpendicular to the dividing direction, as shown in FIG. The prisms 25a and 25b are integrated with a field lens 26, and the pupil image of the photographic lens 1 is transmitted to the aperture 27 provided near the secondary imaging lens 28 via the field lens 26 and the first triangular prism mirror 6.
is imaged. And this secondary imaging lens 28
As a result, the two images in the slits 23a and 23b are formed via the second triangular prism mirror 9 onto the two rows of line sensors 29a and 29b, respectively.

Therefore, the first and second line sensors 29a, 2
9b, two slits 23 of the field mask 24 are shown.
Two images corresponding to a and 23b are formed, and these images are read by line sensors 29a and 29b,
It will generate an electrical output signal. As is clear from FIG. 2, these images are generated by the line sensors 29a and 29b, respectively, by half of the light flux from the pupil of the photographic lens 1, that is, by the light flux that has passed through the secondary imaging lens 28. It is formed by the left and right half luminous fluxes on the pupil of the photographing lens 1. These two images are optically exactly the same as the two images formed on the line sensors 10a and 10b in FIG.
Focus detection can be performed based on the degree of correlation between the output signals from a and 29b.

In the focus detection device according to the present invention, as can be understood from FIG. Problems with the device will be resolved. That is, in the present invention, a more compact line sensor can be used, and the longitudinal dimension of the line sensor of the secondary imaging optical system can be reduced.

In the embodiment, the light splitting means was realized by a one-dimensional microprism, and the light flux shifting means was realized by two prisms having mutually different inclinations.
Of course, these may be replaced with other optical members.

As explained above, the focus detection device according to the present invention has the advantage that it is compact, saves space, and is inexpensive compared to conventional devices.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional focus detection optical system, Figure 2
The following figures show an embodiment of the focus detection device according to the present invention, in which Fig. 2 shows its optical system, Fig. 3 is a developed view of the progress state of light seen from the splitting direction, and Fig. 4 shows an example from the off-axis direction. This is a developed view. Reference numeral 1 is a photographing lens, 22 is a light splitter, 23
a, 23b are slits, 24 is a ranging field mask,
25a and 25b are prisms, 26 is a field lens, 27 is an aperture, 28 is a secondary imaging lens, 29
a and 29b are line sensors.

Claims (1)

[Claims] 1. A field lens is provided near the intended image formation plane of the objective lens, and the pupil image of the objective lens is imaged near a single secondary imaging lens provided behind the field lens, and the secondary image formation Line sensors are arranged in two rows on the image side of the lens, means for dividing the image formed by the objective lens into two images is provided in front of the planned image forming plane, and optical Providing masking means with parallel openings,
Means for shifting the divided light beams in the longitudinal direction of the line sensor is provided between the intended image forming plane and the secondary imaging lens toward the intended image forming plane, so that the image dividing direction and the image A focus detection device characterized in that the shift directions are directions perpendicular to each other, and a focus determination is performed based on an output signal of the line sensor.