JPS58106517A - Optical splitter - Google Patents

Abstract

PURPOSE:To largely take an optical path length difference of a split luminous flux without changing a placing interval of each line sensor, by varying an angle made by each transmitting and reflecting surface of an optical splitting element, and a plane containing each line sensor, to 45 degrees. CONSTITUTION:On a sensor substrate 10, line sensors 11a-11c are plaed, and in its upper part, an optical transmitting plate 12 is installed in parallel with the substrate 10, and furthermore, in its upper part, an optical splitting prism 13 is diagonally provided so that an angle theta made by each transmitting and reflecting surface and the optical transmitting plate 12 becomes <=45 degrees. As image forming luminous flux l from a sub-mirror is made incident to a beam splitter 14a of the optical splitting prism 13, a part of said luminous flux is made incident to the line sensor 11a, the remaining luminous flux is reflected and is made incident to the line sensor 11b, and also goes round outside to the diagonal upper part, and is made incident to the line sensor 11c. As for luminous fluxes lb, lc which have gone round outside, the optical paths are extended by the portion which has gone round outside.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention divides an imaging light beam from a photographic lens, provides a difference in the optical path length of each of the divided imaging light beams, and provides a plurality of light beams arranged to receive each of these light beams. This invention relates to a light splitter used in a focus state detection optical system that detects a focus state by comparing the degree of blur of images obtained by a line sensor.

- A blur detection method is already known in which a light splitter and a plurality of line sensors are attached to an eye reflex camera or the like, and image information from the split imaging light beam is read to detect the in-focus state.

The present applicant has previously disclosed a light splitter using such a system in, for example, Japanese Patent Laid-Open No. 55-155308, which will be explained based on FIGS. 1 and 2. A part of the imaging light flux ρ (only the rays on the optical axis are shown) from an imaging lens (not shown) is transmitted to a partially transmitting quick return mirror 1.
is transmitted, is deflected downward by the sub-mirror 2, and enters the micro prism 3. This prism 3 forms an imaging light beam g
The light beam is divided into three parts and is made to enter the three CCP line sensors 4a, 4b, and 4C while being given a difference in optical path length. Furthermore, the prism 3 and line sensors 4a to 4C
The line sensors 4a to 4C are arranged on the surface of the sensor board 5, and the -
In the prism 3 placed on the light transmitting plate 6 located in the F direction, first and second beam splitters 7a and 7b made of, for example, a dielectric material and a total reflection mirror 7C are sandwiched. The transmissive and reflective surfaces of are arranged parallel to each other and at an angle of 45 degrees with respect to the sensor substrate 5.

Therefore, the light beam ρ that has entered the first beam splitter 7a through the mask 8 is first split into two directions here, and the transmitted light beam ja continues straight and enters the line sensor 4a. The remaining luminous flux is reflected and travels parallel to the sensor board 5, and is transmitted and reflected at the second beam splitter 7b repeatedly.The reflected luminous flux ρb enters the line sensor 4b, and the transmitted luminous flux further The light travels straight parallel to the sensor substrate 5, is reflected downward by the reflecting mirror 7C, and enters the line sensor 4C as a light beam ρC. Therefore, the obtained optical path length difference is the distance between the beam splitters 7a, 7b and the reflection mirror 7c in the direction parallel to the sensor substrate 5. The central line sensor 4b is the planned imaging plane,
That is, it is located at a position conjugate to the film surface, and the line sensor 4a
The line sensor 4C receives images at three different positions in the optical axis direction in the imaging light beam, ie, in front of the planned imaging plane and behind the line sensor 4C,
The degree of blurring of the image at each position is compared using an image sensor to find the in-focus position.

Here, the output signals obtained by each line sensor 4a, 4b, 4C are electrically processed, and as shown in FIG.
Outputs Fa, Fb, and Fc corresponding to respective defocus amounts are obtained from each line sensor 4a, 4b, and 4C. In FIG. 3, the horizontal axis represents the lens extension amount, the vertical axis represents the output value, and F represents the expected imaging plane position=□.

By the way, in this focus detection device, in the region where the lens is extended to infinity, that is, in the region S1 where the amount of lens extension is small, the outputs Fa, Fb, and Fc from each line sensor are extremely small and the size is far apart from each other, so it is a close distance. Area S2
There is a problem in that it is difficult to tell whether the lens extension corresponds to infinity or close range. In order to solve this problem, as shown in FIG. position, one other line sensor 4
C is placed at a position further outside of 4b, and the planned imaging plane F
A focus detection optical system is known that is designed to be arranged asymmetrically with respect to the focus detection optical system to obtain an output as shown in FIG. In this case, the area S where the amount of extension of the photographic lens 8 is reduced is
1, since the output Fc of the line sensor 4C is sufficiently larger than the output Fa of the other line sensors 4a and 4b, the determination can be made more accurately by adding the condition that the amount of extension of the photographic lens 8 is too small. Become.

Is it true that the two-way method is effective when determining the focusing position?In order to make more accurate focusing judgments, it is necessary to increase the optical path length difference between the divided imaging light beams ρa, rays, and βC. It is most effective to do so. As is clear from FIG. 2, a simple means for this purpose is to enlarge the prism 3 in the longitudinal direction and widen the distance between the line sensors 4a, 4b, and 4C. However, each line sensor 4a, 4b
, 4C, the larger the silicon substrate will be required, which will of course lead to an accelerating increase in costs.

The purpose of the present invention is to increase the difference in optical path length between divided light beams, or to shorten the interval between line sensors if the difference in optical path length is present, without changing the arrangement interval between each line sensor. The purpose is to provide a light splitter that can divide an imaging light beam into two or more by a light splitting element, and divide the divided imaging light beams into approximately two or more parts while giving different optical path lengths. In the light splitter that guides the light to each line sensor installed in the same orthogonal or substantially parallel plane, the angle between the transmissive and reflective surface of the light splitting element and the plane containing each line sensor is set to be different from 45 degrees. It is characterized by the following.

The present invention will be explained in detail based on the embodiment shown in FIGS. 6 and 7. In FIG. 6, the sensor board 10 has first, second, and third line sensors 11a, llb, and 11C.
are arranged, and light transmitting plates 12 are installed parallel to the sensor board 10 on one and four sides of the sensor board 10. A light splitting prism 13 is provided on the light transmitting plate 12'' so that its longitudinal direction is oblique to the surface of the light transmitting plate 12. In the prism 13, for example, first and second beam splitters 14a, 14b and a total reflection mirror 14C are provided with surfaces inclined and sandwiched within the prism 13 while maintaining parallel spacing. The angle θ between the transmission and reflection surfaces of these light splitting elements and the surface of the light transmission plate 12 is 45 degrees, preferably 41 degrees or less.

Since the light splitter according to the present invention is configured in this way, the imaging light beam ρ from the submirror is split by the first beam splitter 14a of the light splitting prism 13, and a part of it is split by the first beam splitter 14a. Transmitted and imaged light flux ρa
is incident on the first line sensor lla, and the rest is incident on the first line sensor lla.
The light is reflected by the beam splitter 14a and passes through the light transmitting plate 12.
, in other words, the optical path moving away from the sensor substrate lO,
That is, the optical path is traced diagonally upward along the longitudinal direction of the prism 13. This obliquely upward imaging light beam is further split by the second beam splitter 14b, and a part of the light beam ρb is reflected by the second beam splitter 14b and deflected downward, and the second line sensor llb The remaining light flux passes through the second beam splitter 14b and goes straight as it is, and is reflected by the total reflection mirror 14.
It is totally reflected at c and sent to the third line sensor l as a luminous flux jc.
It will be input to ie. In this process, the optical path of the light beams ρb and ρC incident on the line sensors 14b and 14c is extended by the amount that they are rotated diagonally upward.
The optical path difference between each of the light beams Ja, ρb, and ρC is larger than that in the conventional splitter shown in FIG.

Here, the optical path length difference between the split light beams by the light splitter according to this embodiment and the light splitter shown in FIG. Let's make a concrete comparison. In Fig. 6, the imaging light flux ρa
The emission point from the prism 13 is A, that of the imaging light beam ρb is B, the distance between AB is X, the distance between AB in the surface direction of the sensor substrate 10 is y, and the surface direction of the sensor substrate 10 is If the distance between A and B in the orthogonal directions is 2, and the refractive index of the prism is n, then the optical path length difference between the imaging light beams ρa and 12b will be ((x- y)/nl
It becomes larger by +z. Furthermore, the beam splitter 14a
, 14b and the total reflection mirror 14C and the sensor substrate 10, the angle θ formed by the sensor substrate 10 shows that if a prism material with a refractive index of 1.5183 is used, the optical path length can be increased by 10%. It is sufficient to set the angle θ to 41 degrees and 35 minutes, and to increase it by 50%, it is sufficient to set θ to approximately 28 degrees. Therefore, a sufficient effect can be observed if θ is set to 41 degrees or less.

Next, another embodiment will be explained based on FIG. 7. In this embodiment, by combining a plurality of irregularly shaped prisms,
While the longitudinal direction of the light splitting prism 13 remains parallel to the light transmitting plate 12 and the sensor board 10, the beam splitter 14a,
The angle θ between the transmitting and reflecting surface of the total reflection mirror 14b and the sensor substrate 10 is set to 45 degrees, preferably 41 degrees or less.

In the above embodiment, the imaging light beam p is made to enter the light splitter from a direction substantially perpendicular to the surface of the sensor substrate 10, but in reality, the imaging light beam p is directed almost perpendicularly to the surface of the sensor substrate 10. The light may be incident on the light splitter from parallel directions.

In this embodiment, the imaging light beam ρ passing through the first beam splitter 14a goes straight as it is and becomes the first light beam ja.
is incident on the line sensor lla. The light beam reflected by the beam splitter 14a heads obliquely upward toward the sensor substrate 10, and repeats reflection and transmission as in the embodiment shown in FIG.
It will be incident on . However, these luminous fluxes ρb, ρC
travels straight from the foul point to the line sensors llb and lie without being refracted. In this embodiment, the input point of the imaging light flux ρ to the beam splitter 14a is C1, the reflection point of the light flux ρb at the beam splitter 14b is D, the distance between CDs is X', and the surface of the sensor substrate 10 is Distance between CDs in direction. If y' is the distance between the CDs in the direction perpendicular to the surface direction of the sensor substrate 10, and Z' is the distance between the CDs, the imaging light fluxes ρa and ρ
The optical path length difference with b is (
x' + z' - V' )/n.

In the light splitter according to the present invention configured as described above, the transmitting/reflecting surface of the beam splitter or the like is set at 45° with respect to the sensor substrate.
By providing a simple angle θ of less than 1°, it is possible to minimize the difference in optical path length without increasing the distance between each line sensor, that is, without enlarging the sensor board, and the focus judgment edge □ It is possible to improve the degree of

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a known light splitter, Fig. 2 is a cross-sectional view thereof, Fig. 3 is an output characteristic diagram obtained with a line sensor arranged as shown in Fig. 2, and Fig. 4 is an arrangement of the line sensor. The developed diagram and Figure 5 are the output characteristics obtained from the line sensor with this arrangement.
FIGS. 6 and 7 are configuration diagrams showing an embodiment of a light splitter according to the present invention. 10 is a sensor board, lla, llb, and lie are line sensors, 12 is a light transmitting plate, 13 is a light splitting prism,
14a and 14b are beam splitters, 14c is a reflecting mirror, ρa, ρb, and C are divided imaging light beams, and θ is the angle between the transmitting and reflecting surface of the light splitting element and the sensor substrate. Patent applicant: Canon Co., Ltd. Figure 3 Figure 5"" F 1S2 Figure 6 Figure 7

Claims (1)

[Claims] 1. The imaging light beam is divided into two or more by a light splitting element, and the divided imaging light beams are provided with different optical path lengths while being arranged on the same plane that is substantially orthogonal to or substantially parallel to the imaging light beam. A light splitting device that is characterized in that, in a light splitter that guides the light to each line sensor provided therein, the angle between the transmitting and reflecting surface of the light splitting element and the plane containing each line sensor is different from 45 degrees. vessel. 2. The light according to claim 1, wherein the light splitting element is arranged so that the imaging light beam reflected and split by the light splitting element is reflected and transmitted in a direction away from a plane including each line sensor. divider. 3. Claim 1 in which the angle formed between the transmissive and reflective surface of the light splitting element and the plane containing each line sensor is 41 degrees or less
Light splitter as described in section.