JPS6037509A - Focus detector - Google Patents

Abstract

PURPOSE:To obtain a focus detector which lends itself to various kinds of photographing lenses and has high accuracy by such constitution in which the phase shift of the signals from sensor arrays in a focusing state is corrected. CONSTITUTION:A photoelectric converting means 11 contg. sensor arrays 6a, 6b transmits the output signal from a sensor array 6a which receives the luminous flux from a region 1b of the exit pupil of a photographing lens and the output signal from a sensor array 6b which receives the luminous flux from the region 1a of the exit pupil to a phase difference detector 12. The detector 12 detects the phase difference DELTA of the two output signals and transmits the same to a substracting device 14. The device 14 decreases the initial phase difference DELTA0 stored in a storage device 13 from the DELTA and transmits the corrected phase difference DELTA3=DELTA-DELTA0 to a focus discriminating device 15 which judges the focusing when DELTA3=0, judges the front focus and the rear focus by the code of DELTA3 and the absolute value and transmits the defocus quantity to a focusing state display device 16. The focus detector having high accuracy is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus detection device to be built into, for example, an automatic focus camera.

Conventionally, as this type of focus detection device, a method has been widely adopted in which focus detection is performed using light beams from two areas symmetrical to the optical axis in the exit pupil of a photographic lens. In this method, two images are projected onto a pair of sensors as described later.
There is a drawback that a phase difference occurs between the two images even in the focused state due to lens aberration, reducing accuracy.

Here, conventional focus detection devices and their problems will be explained with reference to FIGS. 1 to 3. FIG. After the light beams in two regions 1a and 1b symmetrical to the optical axis in the exit pupil of the lens 1 are imaged by the field mask 2 on the primary imaging plane, a splitting prism 4 consisting of a field lens 3 and prisms 4a and 4b is formed. The image is projected onto sensor arrays 6a and 6b of a self-scanning sensor 6 arranged at a position conjugate with the primary imaging plane and the film plane through the secondary imaging lens 5, and the outputs from these sensor arrays 6a and 6b are projected. The in-focus state is detected based on the phase difference of the signals.

The sensor array 6a has an exit pupil area 1b of the photographing lens 1.
After once converging on the field mask 2, the light flux from the area 1a is bent by the prism 4a and enters the sensor array 6b.Similarly, the light flux from the area 1a is bent by the prism 4b and enters the sensor array 6b.

Therefore, the output signal of each sensor array 6a, 6b becomes a signal representing the object image formed by the light flux coming from the corresponding exit pupil area 1b, ]a. In this way, the light beams from the two exit pupil regions 1b, 1a are deflected vertically by the prisms 4a, 4b, so that in the focused state, the light beams are reflected by n pixels Ai, Bi of the sensor arrays 6a, 6b, respectively. Ideally, the light beams from the same location on the subject are projected, and the output signals of the sensor arrays 6a and 6b also match without any phase difference, as shown in FIG.

However, the light beam that has passed through the lens cannot be converged to one point due to the aberrations of the lens, and is formed as a spread image. For this purpose, when the light beam incident on the secondary imaging lens 5 is divided by the prisms 4a and 4b and projected onto the respective sensor arrays 6a and 6b as shown in FIG.
As shown in FIG. 3, the two images projected onto the sensor arrays 6a and 6b produce a phase difference Δ even in the focused state due to the aberration of the lenses, resulting in a shift in focus.

An object of the present invention is to eliminate such conventional drawbacks and provide an extremely accurate focus detection device. A photoelectric sensor pair consisting of a plurality of light receiving elements is arranged, a phase difference detection means is provided for detecting a phase difference between the output signals of the photoelectric sensor pair, and the focus of the photographing lens is detected based on the output signal of the phase difference detection means. This focus detection device is characterized by comprising a correction means for correcting the output signal of the phase difference detection means when the photographic lens is in a focused state.

Next, the principle of the present invention will be explained with reference to FIGS. 4 to 9. In these drawings, the same reference numerals as in FIG. 1 represent the same members. When the photographing lens l is in focus on the field mask 2 which is conjugate with the film plane, it passes through the two areas 1b and 1a of the exit pupil and forms a pair of sensor arrays 6a and 6b, as shown in FIG. A deviation occurs between the two subject images projected above. That is, as shown in FIG. 5, this phase difference Δ0 occurs in the output signals of the sensor arrays 6a and 6b. . Here, when the sensor array 6b is taken as a reference, this phase difference Δ0 becomes a negative value. Next, when the front is in focus as shown in FIG. 6, the phase difference Δ1 is further shifted in the same direction as the direction of shift in FIG. 5, as shown in FIG.
occurs and takes a negative value. Further, when the rear focus state is set as shown in FIG. 8, a phase difference Δ2 is generated in the opposite direction to the direction of shift in the front focus state, as shown in FIG.

The sign of this phase difference Δ2 changes depending on the defocus amount of the front focus.

FIG. 1O is a block diagram showing an arithmetic processing system according to an embodiment of the present invention. In this FIG. 10, the sensor array 6a
, 6b converts the output signal of the sensor array 6a which receives the light flux from the exit pupil region 1b of the photographing lens 1, and the output signal of the sensor array 6b which receives the light flux from the exit pupil region 1a of the photographic lens 1. The signal is sent to the phase difference detection device 12. Then, the phase difference detection device 12 detects the phase difference Δ between the two output signals and transmits it to the subtraction correction device 14.

The storage device 13 stores the initial phase difference Δ0 at the time of focusing, and the subtraction correction device 14 calculates the initial phase difference Δ0 from the phase difference Δ.
The corrected phase difference Δ3=Δ−Δ0 is sent to the focus determination device 15, and when Δ3=0, it is determined that the focus is in focus, and depending on the sign and absolute value of Δ3, it is front focus or rear focus. This judgment and the amount of defocus are detected, and the output signal is sent to the photographic lens driving device or the focus state display device 16.

FIG. 11 shows a further improved embodiment. In cameras with various interchangeable lenses, vignetting occurs in the exit pupil due to the difference in the exit pupil diameter of the photographic lens, causing unevenness in the distribution of the amount of light projected onto the sensor array, making it difficult to accurately detect focus. I have a problem. In order to improve this problem, in the embodiment shown in FIG. 11, there are four regions symmetrical to the optical axis in the exit pupil of the photographic lens 21, that is, two large regions 21a and 21b, and a Two small areas 21
The light beams c and 21d are passed through the field mask 22, which becomes the -order imaging plane.
After forming an image, the image is projected onto sensor arrays 26a to 26d of a self-scanning sensor 26 arranged at a position conjugate with the primary imaging plane via a field lens 23, a splitting prism 24, and a secondary imaging lens 25. These sensor arrays 2
The in-focus state is detected based on the phase difference between the output signals from 6a to 26d. Note that 27 indicates an aperture frame.

The light flux that has passed through the region 21a is once converged on the primary imaging plane, and then is deflected by the prism 24a and enters the sensor array 26a. Similarly, the sensor array 26b has a region 21. The light beam passing through b and the sensor array 26c
The light flux that has passed through the area 21c is incident on the sensor array 26d, and the light flux that has passed through the area 21d is incident on the sensor array 26d. Therefore,
When the exit pupil diameter of the photographic lens 21 is large, focus detection is performed by interpreting the sensor arrays 26a and 26b that detect the light flux passing through the large areas 21a and 21b, and detecting the phase difference of the output signals. conduct. Shooting lens 2
When the diameter of the exit pupil 1 is small, the sensor arrays 26c and 26d are selected to detect the light flux passing through the small areas 21c and 21d of the exit pupil 2, and the focus is detected by detecting the phase difference of their output signals. I will do it.

When the light beam passing through the areas 21a and 21b of the photographing lens 21 is projected onto the sensor arrays 26a and 26b, and when the area 2
The light flux passing through 1c and 21d is sent to the sensor array 26c,
26d, a phase difference Δ is generated in the output signals of the respective sensor arrays 26a to 26d due to the above-mentioned lens aberration, but the position of the output signals of the sensor arrays 28a and 26b is The phase difference Δ0 and the phase difference Δ0' between the output signals of the sensor arrays 26c and 26d vary quantitatively as shown in FIGS. 12 and 13. In general, the quantity is larger when a wider luminous flux is taken in.

FIG. 14 shows an example of an arithmetic processing system when the configuration shown in FIG. 11 is adopted. Sensor array 26a
26d, the output signals of the sensor arrays 26a to 26d that receive the respective light beams passing through the respective areas 21a to 21d of the exit pupil of the photographic lens 21 are selected by the selection device 17, and the output signals of the sensor arrays 26a to 26d are selected by the selection device 17, 12. The phase difference detection device 12 detects the phase difference Δ between the two selected output signals and sends it to the subtraction correction device 14 . The storage device 13 stores initial phase differences Δ0 and Δ0° at the time of focusing, and one of the initial phase differences Δ0 and Δ0° corresponding to the sensor array selected by the aforementioned selection device 17 is selected and subtracted. It is sent to the correction device 14. Then, the subtraction correction device 14 subtracts the initial phase difference Δ0 or Δ0'' from the phase difference Δ, and the corrected phase difference Δ3=Δ−Δ0, or Δ3=
Δ-Δ0' is sent to the focus determination device 15, and when Δ3=O, it is determined that the focus is in focus. If Δ3 is not O, it is determined whether the front focus is in focus or the rear focus is based on the sign of Δ3, and the defocus M is detected from the absolute value of Δ3, and the output signal is sent to the photographic lens driving device or the focus state display device 16. The lens drive or focus state is displayed.

In this case, the selection device 17 of the sensor arrays 26a to 26d
manually selects the arbitrary sensor array 26a according to the will of the photographer.
~26d may be selected, or the sensor arrays 26a~26d may be selected from the open F value of the photographic lens 21.
may be selected.

It is also possible to select the sensor arrays 26a to 26d based on information about the size of the exit pupil diameter of the photographic lens 21.

As explained above, according to the focus detection device according to the present invention, the accuracy of this type of focus detection device can be greatly improved by correcting the phase shift of the output signal of the sensor array in the focused state. It becomes possible. In addition, by incorporating light beams from different areas of the exit pupil of the photographic lens and correcting the phase shift of each output signal of the sensor array, we have created a relatively simple and highly accurate focus detection device that can be used with various photographic lenses. The effect that it can be configured by means is remarkable.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a conventional focus detection device, Figs. 2 and 3 are waveform diagrams of output signals, Figs. Fig. 5 is a waveform diagram of the output signal, Fig. 6 is a ray diagram of the front focus state, Fig. 7 is a waveform diagram of the output signal in that case, Fig. 8 is a ray diagram of the rear focus state, FIG. 9 is a waveform diagram of the output signal, FIG. 10 is a block diagram of the arithmetic processing system, FIG. 11 is a configuration diagram of another embodiment, FIGS. 12 and 13 are waveform diagrams of the output signal, and FIG. 14
This figure is a block diagram of an arithmetic processing system corresponding to the embodiment of FIG. 11. Symbol l, 21 is a photographing lens, 2.22 is a field mask, 4
．． 24 is a splitting prism, 5.25 is a secondary 1 tA image 1y ance, e, 26 is a sensor + l-16a, 6
b, 26a to 26d are sensor arrays, 11 is a photoelectric conversion means, 12 is a phase difference detection device, 13 is a storage device, 14 is a subtraction correction device, 15 is a focus determination device, 16 is a focus state display device, and 17 is a It is a selection device. Patent Applicant: Canon Co., Ltd. 2 Figure 14: Teito Sales tF-'j'ヰ (Voluntary) December 30, 1980 Director General of the Patent Office Kazuo Wakasugi S\1, Indication of Case 1988 Patent Application No. 145066 2, Name of the invention Focus detection device 3, Relationship with the person making the amendment Case Patent application filing address 3-30-2 Shimomaruko, Ota-ku, Tokyo Name (10
0) Canon Co., Ltd. Representative Ryu Kaku Sanbe 4, Agent Address: 2-17-3 Umejima, Adachi-ku, Tokyo 121 Umejima Hightown C-104 m03 (852) 3111■ - Drawing 6, Contents of amendment Drawing 11 Correct the undelivered copy of the attached paper. Fig. 10 24 and Fig. 11 27 Kou 3 (' ・ 2 1o21- ( ) b ・ (, -m-・" Sumata Ryu) Fig. 12 ""'21b,. 516 21813 Fig. Δ0

Claims (1)

[Claims] 1. Pairs of photoelectric sensors each consisting of a plurality of light-receiving elements are arranged at positions optically conjugate with the planned focal plane of the photographic lens, and the phase difference between the output signals of these pairs of photoelectric sensors is detected. A focus detection device is provided with a phase difference detection means for detecting a focus of a photographing lens based on an output signal of the phase difference detection means, the focus detection device comprising: A focus detection device comprising a correction means for correcting an output signal. 2. Two or more pairs of photoelectric sensors are arranged, and a selection means is provided for selecting one of the pairs, and the phase difference detection means detects the phase difference between the output signals of the pair of photoelectric sensors selected by the selection means. The focus detection device according to claim 1, wherein the focus detection device detects the focus by detecting the focus.