JPS63265210A - Focus detector - Google Patents

Abstract

PURPOSE:To enable focus detection by near IR light as well by eliminating the influence of an IR aberration on the output from a means for detecting a defocusing quantity in accordance with the information on the IR aberration intrinsic to a photographing lens from a means for storing lens information and the output from a means for discriminating IR light. CONSTITUTION:A pair of IR cut filters 20 having different shielding characteristics respectively control the spectral characteristics of split pupil luminous fluxes. The means 34 for discriminating the IR light receives the outputs from a pair of photoelectric converting means 1 and detects the degree of the influence of the IR aberration on the output of the means 33 for detecting the defocusing quantity. A means 35 for correcting the IR aberration receives the output from the means 33, the information on the IR aberration intrinsic to the photographing lens from the means for storing the lens information and the output from the means 34 and corrects the IR aberration of the photographing lens as against the output from the means 33, thereby correcting beforehand the influence of the IR aberration in focus detection. Since the degree of the influence of the IR aberration is thereby discriminated, the IR aberration to cause an error in the focus detection is easily corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus detection device used in a TTL camera or the like to which an interchangeable lens can be attached, and particularly relates to a focus detection device that is capable of correcting infrared aberrations that the interchangeable lens has. .

``Prior art'' Each focus detection device photoelectrically converts subject light that enters through a lens with infrared aberration using a photodetector that is sensitive to visible and non-visible wavelengths, and converts the resulting output into There are some that perform focus detection.

FIG. 1 shows an example of a focus detection device for a camera, which detects the shift of two images formed by dividing the pupil of a photographic lens and determines the focus adjustment state of the photographic lens. The light fluxes that have passed through the first and second regions 11a and llb of the exit pupil, respectively, form first and second subject images in the vicinity of the intended image plane 12.

The first and second subject images are transmitted to the first and second re-imaging lenses 1 through the field lenses 13, respectively.
4.15 generates an output pattern corresponding to the subject image intensity distribution on the first and second photoelectric conversion units 16 and 17 of the photoelectric conversion element array (hereinafter referred to as an image sensor) 1, and detects the amount of defocus described later. A relative shift between these patterns is detected by the means, and the focus adjustment state of the photographic lens 11 is determined from the amount of shift.

Such a focus detection device performs different focus detections for light of different wavelengths due to infrared aberration of the photographing lens.

Most photoelectric converters are P-N junction type PDs, and their sensitivity extends from the visible region to the near-infrared region. When the subject is illuminated by a light source with a high color temperature, such as daylight or fluorescent light, focus detection will be performed differently depending on the infrared aberration of the photographic lens.

In particular, the amount of infrared aberration is large when the camera lens is a photographic lens or a long focal length lens.If a long focal length lens is attached to a TTL camera and focus detection is performed, the focus detection error due to infrared aberration may be significant, depending on the light source. , the film surface differs by several hundred microns, making it impossible to accurately detect focus.

As a means to eliminate such focus detection errors, the cutoff wavelength of the infrared cut filter is set to the upper visible limit (670-68
It may be possible to set it to 0ns).

However, in this case, a) information from near-infrared light is discarded, resulting in a large loss of light quantity and a decrease in focus detection ability when subject brightness is low.

Note) If the subject brightness is very low, it is impossible to detect the focus as it is, and in the case of a system that performs focus detection using auxiliary light irradiation, the light source used for auxiliary illumination or visible light is POW.
Even if there is an ER, it is dazzling, and in the case of near-infrared light, the cut-off wavelength of the infrared cut filter or the upper limit of visible light may cause problems such as not being able to produce much output.

In order to solve these problems, the present applicant has
-86504, we proposed a method to supplement infrared aberration by providing a color temperature sensor.

``Problem to be solved by the invention'' However, even with the above-mentioned proposed technology, the focus detection area and the color temperature detection area do not necessarily correspond, and when the light source is mixed, it is difficult to accurately detect the focus detection area. Since the color temperature cannot be determined, accurate aberration correction cannot necessarily be performed, and a color temperature sensor is required as an additional light-receiving element, so it takes up space in cameras that require miniaturization. There was a problem.

The present invention does not limit the wavelength region in which focus detection is possible to the visible region, that is, it enables focus detection using near-infrared light, and at the same time, the infrared rays of the photographic lens can be detected without using an additional light receiving element. It is an object of the present invention to provide a focus detection device that eliminates focus detection errors caused by aberrations.

"Means for Solving the Problems" The gist of the present invention for achieving the above object is to provide a pupil dividing means (14) for dividing a light beam for focus detection out of the light transmitted through the photographic lens (11). ), a pair of photoelectric conversion means (1) receiving the divided pupil light flux, and receiving the output from the pair of photoelectric conversion means (1), the photographing lens (11
), the focus detection device is equipped with a defocus amount detection means (33) for detecting the amount of defocus up to the in-focus position of the photographic lens (11). A lens information storage means (42) that fixedly stores various information including external aberration information, and a pair of infrared cut filters (20) installed in the optical path of the divided pupil light flux and each having different spectral characteristics. and infrared light identification means (34) that receives the outputs from the pair of photoelectric conversion means (1) and detects the degree of influence of infrared aberration on the output of the defocus amount detection means (33). .

Based on the infrared aberration information specific to the photographing lens from the lens information storage means (42) and the output from the infrared light identification means (34), the The focus detection apparatus includes an infrared aberration correction means (35) that performs correction so as to remove the influence of infrared aberration.

"Function" A pair of infrared cut filters with different cutoff characteristics are
The spectral characteristics of the divided pupil light fluxes are each defined, and the infrared light identification means receives the outputs from the pair of photoelectric conversion means and detects the degree of influence of infrared aberration on the output of the defocus amount detection means. do.

The infrared aberration correction means detects the amount of defocus by receiving the output from the defocus amount detection means, the infrared aberration information specific to the photographing lens from the lens information storage means, and the output from the infrared light identification means. The infrared aberration of the photographing lens is corrected for the output from the means, and the influence of the infrared aberration on focus detection is corrected in advance.

"Example" Hereinafter, the present invention will be described in detail based on the drawings.

Note that in the description of each embodiment and the prior art, similar parts are given the same reference numerals, and redundant description will be omitted.

1 to 3 show a first embodiment of the present invention.

FIG. 1 is an overall view of the focus detection device, FIG. 2 is a pair of infrared cut filters arranged in front of a pair of photoelectric conversion means, which are the components of this embodiment, and FIG. An example of spectral transmission characteristics of an outer cut filter is shown.

In FIG. 1, an image sensor l including a pair of photoelectric conversion means is disposed after the focus detection optical system including the photographing lens 11, and a pair of infrared cut filters 20 are disposed in front of the image sensor l. There is. As shown in FIG. 3, the pair of infrared cut filters 20 correspond to the pair of photoelectric conversion units 16 and 17, and each has nine different transmission bands.

An A/D converter 31 is provided to receive the output of the image sensor l. Specifically, the A/D converter 31 outputs an A output (when the number of elements is n, the time series output is a 1.a2.a3.,,,,an
), and the output of the photoelectric conversion unit 16 that receives the light flux passing through the other pupil region 11b is B output (when the number of elements is n, the time series output is bl, b2.b3., , , bn). , the A/B outputs, which are the brightness distribution pattern of the optical image, are alternately A/D-exchanged, and the respective output data are stored in the memory 32.

Next to the memory 32, a defocus amount detection means 33 and an infrared light identification means 34 are provided.

The defocus amount detecting means 33 calculates the amount of deviation between the A output and the B output by correlation calculation, and calculates the amount of image plane deviation of the optical image. Such correlation calculations and the like are disclosed in Japanese Patent Laid-Open No. 60-37513 filed by the present applicant.

The infrared light identification means 34 detects the degree of influence of infrared aberration on the amount of shift determined by the defocus amount detection means 33.

For example, if the output of a pair of photoelectric conversion means is as shown by the solid line in Figure 7, and the influence of infrared aberration is detected by the ratio of the difference and sum of their average values, specifically, 32, calculate the average value of the A output A - (1/port) × (Σai) and the average value of the B output B = (1/n) Data value C (A, B) representing the influence of aberration
Calculate.

C(A,B) = (A-8)/(A+B)...(1
) A detailed explanation will be given later, but it is generally considered that the larger the value of C (A, B), the greater the influence of infrared aberrations.

The lens information storage means 42 in which aberration information specific to the photographic lens is stored is a ROM provided inside the photographic lens 11.
It is composed of fixed memory elements such as. In focus detection, the main aberrations that cause detection errors are spherical aberration and chromatic aberration.Since only chromatic aberration is considered here, spherical aberration will be omitted.

In a specific example of the present invention, the aberration value of the A' line is fixedly stored as the chromatic aberration information in the lens information storage means 42;
'The linear aberration data is sent to the communication line 4 along with other data.
0 to the infrared aberration correction means 35.

The infrared aberration correction means 35 uses the output C of the infrared light identification means 34.
(A, B), the A'-line aberration data D(A) of the lens information storage means 42, and the defocus amount Df calculated by the defocus amount detection means 33, and corrected defocus amount that corrected chromatic aberration. D f((:) below (2)
Calculate using the formula.

D f (C) = D f + D (A) * k * C
(A, B)...(2) The drive display control means 36 is connected to the infrared aberration correction means 35, and the drive display control means 36
Upon receiving the output from the infrared aberration correction means 35, the focus alignment state of the photographic lens 11 is transmitted to the display means 37, and at the same time, the photographic lens 11 is automatically brought into focus via the motor 38 which is a driving means. .

A detailed description of the first embodiment will be given below with reference to other drawings.

FIG. 2 is a schematic diagram of the image sensor 1 and the infrared cut filter 20 viewed from the photographing lens side, and a pair of photoelectric conversion units 16 and 17 are arranged in the direction of pixel arrangement.

The infrared cut filter 20 is formed by multilayer coating on a common glass substrate, and has different cutoff characteristics depending on the photoelectric conversion sections 16 and 17. FIG. 3 shows the respective cutoff characteristics.

Here, the infrared cut filter corresponding to the photoelectric conversion unit 16 is 20A, and the infrared cut filter corresponding to the photoelectric conversion unit 17 is 20B.The filter characteristics of the two are slightly different, perhaps only in the near-infrared cutoff wavelength. Here, if the cutoff wavelength for 50% transmission is 750, then the infrared cut filter 20A has a T50 of 740 nm, and the filter 20B has a T50 of 770 nm.
The transmission range of 30 ns and 30 ns is different. Therefore, C (A, B) calculated in (1) represents the near-infrared content of the reflected light from the subject.

The spectral characteristics of light sources used for photography can be roughly classified as follows.

a) There is a lot of infrared light.

(Tungsten, halogen...A light source) b) Infrared light and visible light or the same level (daylight, B light source) C) Contains almost no infrared light (fluorescent light, High pressure sodium, M halide...C
(Light source) Therefore, if you can identify the A, B, and C standard light sources, you will have no trouble taking photographs.

From this perspective, infrared aberrations can be sufficiently corrected by knowing the near-infrared content of the reflected light from the object. The spectral characteristics of standard light sources A, B, and C are shown in Figure 4.
The figure shows the output when using the above light source. As can be seen from Figure 5, C obtained using equation (1) for each light source
Since the values of (A, B) are different, conversely C(A,
The light source can be identified from the value of B).

In this case, the infrared cut filter may be formed on a common glass substrate by multilayer coating, or, of course, may be formed on two separate glass substrates and bonded together.

The setting value of T2O is not limited to the above value, but for example 770.
It may be 800 nm.

However, d is preferably about 20-40 ns.

Next, infrared aberration data specific to the photographing lens will be explained as specific information in the lens information storage means. FIG. 6 shows the chromatic aberration of a typical photographic lens.

In the near-infrared region, the amount of aberration changes almost linearly with wavelength, so by taking, for example, A'-line aberration as infrared aberration data and multiplying that value by an appropriate coefficient, infrared The amount of aberration can be estimated.

In the first embodiment described above, the infrared light identification means detects the degree of influence of infrared aberration by calculating the ratio of the DC components of the outputs of the pair of photoelectric conversion means, that is, the ratio of the average values.

However, even if the object contains an infrared component, if it has contrast in the visible region and no contrast in the infrared region, a difference occurs in the DC component, and it is therefore determined that there is an influence of infrared aberration.

On the other hand, since the focus detection calculation detects the phase difference of the object contrast, the amount of defocus can be determined without being affected by infrared aberration. Therefore, in such a case, there is a possibility that infrared aberration correction may not be performed correctly.

The second embodiment improves the above-mentioned drawbacks, in that the infrared light identification means of the first embodiment has a
While the influence of infrared aberration is detected by calculating the ratio of C components, the infrared light identification means of the second embodiment calculates the ratio of AC components of the outputs of a pair of photoelectric conversion means to detect the influence of infrared aberrations. The difference is that the degree of influence of external aberrations is detected.

The configuration of the second embodiment is the same as that of the first embodiment, so it will be omitted and only the infrared light identification means will be explained.

FIG. 8 shows the output (
A, B output) -th differential output (AI.

Bl output).

By performing first-order differentiation, it is possible to remove the DC component from the A and B outputs and extract only the ACm component. Therefore, the degree of influence of infrared aberration can be detected by taking the area ratio of the shaded area in FIG.

Specifically, the data value C (A, B
) is determined.

C(AI, Bl) = (AI-Bl)/(^1481
) ・-(3) Tatashi AI-Σl a i-a (
i+g) l ・-(4) Bl-Σl b i-b
(i+g) l - (S)g is an arbitrary constant between 1, 2.3 and above.
By using it instead of A and B), infrared aberration correction can be performed.

In the above embodiment, the data C (Al, Bl) regarding the degree of influence of infrared aberration was obtained from data obtained by first-order differentiation of the outputs of a pair of photoelectric conversion means, but the data C (Al, Bl) regarding the degree of influence of infrared aberration is not limited to this. It may be any value that corresponds to the AC component (contrast) of the output of the photoelectric conversion means, such as (maximum value - minimum value) of the output of the photoelectric conversion means.

As described above, in the second embodiment, the degree of influence of infrared aberration is detected from the ratio of the AC component 7 obtained by performing first-order or higher differentiation on the outputs of the pair of photoelectric conversion means and removing the DC component. The degree of influence of the infrared component on the object contrast used in the focus detection calculation can be detected correctly, and the above-mentioned drawbacks can be solved.

Further, in the above embodiment, the infrared aberration correction means 35 is (2)
Although the correction as shown in the formula was performed, the infrared light identification means 34
Output data from C(A, B) or C(^1,81)
By receiving and comparing these data with predetermined values (
Defocus amount correction as shown in equation 6) may be performed.

If C(A, B) or C(AI, 81) < Cex, D fc= D f...(6) If C(A, B) or C(AI, 81) 2 Cex, D fc= D f order D (A) X h = (
6) However, h: constant coefficient, Cex: more than a predetermined value, data C related to the infrared aberration influence degree detected by the infrared light identification means 34 in the first and second embodiments.
(A, B) and C(At, Bl) are used in the defocus correction means 35 or are sent to the defocus amount detection means 33 as shown in FIG. 7) Calculate the formula to obtain data ai' and bi' that match the levels of the DC component or AC component, and perform focus detection calculations on these data to perform focus detection calculations with higher accuracy. It comes.

ai'=aix (1-C(A,B)), bi'-b
ix (1-C(A,B)) or ai'-aiX (
1+ (Al, Bl)), bi'=bix (1+C
(AI, Bl)) However, i-1 to n...(7) In the above embodiment, a pair of infrared filters having different blocking characteristics were installed in front of a pair of photoelectric conversion means, or It may be placed anywhere in the optical system as long as it is constructed so that the light flux guided to the pair of photoelectric conversion means passes through a pair of infrared filters each having a different blocking characteristic. For example, in FIG. 1, a pair of infrared cut filters may be installed near the re-imaging lenses 14 and 15, or the pair of re-imaging lenses themselves may have the characteristics of a pair of infrared cut filters. Good too.

[Effects of the Invention] According to the focus detection device according to the present invention, since the degree of influence of infrared aberrations can be identified, it is possible to easily correct infrared aberrations that result in focus detection errors. Not only does it not require a dedicated sensor, which is a big advantage for small cameras, but
Since the infrared light identification area is exactly the same as the focus detection area, it is highly effective in terms of accuracy even when different types of light sources are mixed.

[Brief explanation of the drawing]

1 to 6 show a first embodiment of the present invention,
Figure 1 is a conceptual diagram of the W component of the focus detection device, Figure 2 is a layout diagram of a pair of infrared cut filters, Figure 3 is a diagram of the spectral transmission characteristics of a pair of infrared cut filters, and Figure 4 is a diagram of various light sources. A spectral characteristic diagram, FIG. 5 is an explanatory diagram of the infrared light discrimination means, FIG. 6 is a chromatic aberration characteristic diagram of the photographing lens, FIGS. 7 and 8 are explanatory diagrams of the second embodiment, and FIG. 8 is a diagram showing the output side of a pair of photoelectric conversion means, FIG. 8 is a first-order differential characteristic diagram of the above-mentioned output, and FIG. 9 is a diagram showing the configuration of a main part of another focus detection device. 1... Image sensor 11... Taking lens 31... AD conversion means 32... Memory means 34... Infrared light identification means 33... Defocus amount detection means 35... Infrared aberration correction hand protection

Claims (3)

[Claims] (1) A pupil dividing means that divides the light flux for focus detection out of the light transmitted through the photographic lens, a pair of photoelectric conversion means that receives the divided pupil light flux, and a pupil division means that receives the output from the pair of photoelectric conversion means. , a focus detection device comprising: a defocus amount detection means for detecting a defocus amount up to the in-focus position of the photographing lens; various information included in the photographing lens, including infrared aberration information specific to the photographing lens; a pair of infrared cut filters installed in the optical path of the divided pupil light beams and each having different spectral characteristics; an infrared light identification means for detecting the degree of influence of infrared aberration on the output of the defocus amount detection means, infrared aberration information specific to the photographing lens from the lens information storage means, and the infrared light and infrared aberration correction means for correcting the output from the defocus amount detection means so as to remove the influence of the infrared aberration, based on the output from the identification means. (2) The infrared light identification means receives outputs from the pair of photoelectric conversion means, calculates a ratio of DC components of the pair of outputs, and makes a discrimination. The focus detection device described. (3) The infrared light identification means receives outputs from the pair of photoelectric conversion means, calculates and discriminates the ratio of AC components of the pair of outputs, The focus detection device described in .