JPH0456812A - focus detection device - Google Patents

Abstract

PURPOSE:To make it unnecessary to use a detecting means for detecting the position of a diaphragm and to prevent focus detecting accuracy from being dropped due to the switching of the diaphragm by correcting and converting a sensor signal output by a parameter so as to correct the deviation of a diaphragm aperture from the normal position of a centroid position at the time of changing the aperture shape of the diaphragm. CONSTITUTION:The focus detector is provided with a correlation arithmetic means 62 for detecting relative positional relation between a pair of light distribution elements by a correction/conversion signal outputted from a correcting/converting means 61 and executing focus detection based upon the correction/conversion signal found out by a determined parameter and a parameter determining means for determining one parameter value from the results of the means 62 which are obtained from at least three different parameters. The deviation of the aperture from the normal position of the centroid position is corrected at the time of changing the aperture shape of the diaphragm by correcting/converting the sensor signal output by ;the parameter. Consequently, a new detecting means for detecting the position of the diaphragm is not required and th focus detection accuracy can be prevented from being dropped due to the switching of the diaphragm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in a focus detection device disposed in a camera or the like.

(Background of the Invention) Various types of focus detection devices for cameras and the like have been proposed, and an example thereof is shown in FIG.

In Fig. 5, 1 is an objective lens, 2 is a field mask placed near the planned focal plane of objective lens 1, 3 is also a field lens, and 4 is placed symmetrically with respect to the optical axis of objective lens 1. A secondary optical system composed of two lenses 4-1.4-2, 5 denotes the two lenses 4-1.4-
Two sensor rows 5- corresponding to 2 and arranged behind it
1° 5-2; 6 is a diaphragm having two openings 6-1.6-2 arranged corresponding to the two lenses 4-1.4-2; 7 is a divided sensor; The exit pupil of the objective lens 1 constituted by two regions 7-1 and 7-2 is shown. Note that the field lens 3 has the aperture 6-1, 6-2 located in the exit pupil area 7-1 of the objective lens 1.
It has the effect of forming an image in the vicinity of 7-2, and each area 7-
The light beams transmitted through the sensor arrays 5-1 and 5-2 form light quantity distributions on the sensor arrays 5-1 and 5-2, respectively.

In the focus detection system shown in FIG. 5, when the imaging point of the objective lens 1 is in front of the planned focal plane,
When the light intensity distributions formed on -1.5-2 are close to each other and the imaging point of the objective lens 1 is behind the planned focal plane, the two sensor rows 5-1.5 -2
The light quantity distributions formed on each side are separated from each other. Since the amount of deviation in the light intensity distribution formed on the two sensor rows 5-1 and 5-2 has a certain functional relationship with the amount of defocus of the objective lens 1, the amount of deviation is calculated by an appropriate calculation means. Then, the direction and amount of defocus of the objective lens 1 can be detected.

A method for calculating the amount of deviation between the two light intensity distributions described above is disclosed, for example, in Japanese Patent Laid-Open No. 107313/1983 by the present applicant. The easiest way to calculate the amount of defocus d of the objective lens 1 from the amount of deviation M between the two light intensity distributions obtained from this is to use the constant of proportionality K, assuming that both are approximately proportional, and calculate d=-M...・(1)
This is determined by the following. Furthermore, by improving this formula, d and M
An arithmetic method that takes into account the nonlinearity of is also disclosed by the present applicant in Japanese Patent Application Laid-Open No. 107311/1983, but a detailed explanation will be omitted here.

In such a focus detection device, in order to perform accurate focus detection, the common portion of the light amount distribution formed on the two sensor rows must be the same.

The first condition for this is that the light quantity levels of the two light quantity distributions must match. FIG. 6 shows a cross section of the objective lens 1 in FIG. 5 on the exit pupil 7 plane.

In FIG. 6(a), 8 is the exit pupil of the objective lens 1, and 9
-1.9-2 indicates the projected image of the aperture 6-1.6-2 of the aperture 6 formed by the field lens 3 on the exit pupil plane, that is, the entrance pupil of the focus detection system. Since the amount of light on the sensor surface is considered to be proportional to the area of the entrance pupil of the focus detection system, the exit pupil 8 of the objective lens 1 is located at the entrance pupil 9-1.9 of the focus detection system as shown in FIG. -2, two sensor rows 5-1°5-
The amount of light on 2 becomes equal. On the other hand, as shown in FIG. 6(b), for example, some error occurs, and the objective lens 1
When a part of the entrance pupil 9-2 of the focus detection system is blocked by the exit pupil 8 of the lens, the amount of light on the corresponding sensor row 5-2 decreases.

On the other hand, as shown in Fig. 6(C), the entrance pupils 9-1 and 9-2 of the focus detection system are not completely included in the exit pupil 10 of the objective lens 1, but the occluded side of the two is symmetrical. If 2
The decrease in the amount of light on the two sensor rows 5-1 and 5-2 is the same, and the light amount levels match. However, Fig. 6 (
C) is a special condition, and if there is even a slight error, 2
If the blocked side of the two entrance pupils becomes asymmetrical, the light levels will not match. Therefore, when constructing a focus detection system as shown in FIG. 5, even if a certain amount of error occurs as shown in FIG. 6(d), the entrance pupil 11-1.
The size of the diaphragm aperture 6-1, 6-2 of the focus detection system is determined with sufficient margin so that the exit pupil 8 of the objective lens 1 does not block the exit pupil 8 of the objective lens 1. Especially when the photographic lens, which is the objective lens, is replaceable, such as in an eye reflex camera, the aperture aperture is set small to match the one with the smallest exit pupil diameter of all the photographic lenses that should be available. There is a need to. In this case, for a bright photographic lens, focus detection is performed at the expense of brightness and accuracy.

As one solution to these problems, a method has been proposed in which the aperture size of the aperture in the focus detection system is made variable according to the brightness of the photographic lens. Classified into three categories based on the aperture F number: standard brightness lenses, bright lenses, and dark lenses.
For each, a diaphragm having an aperture size and shape as shown in FIGS. 7(a), 7(b), and 7c is selected and used by arranging it in correspondence with the secondary optical system 57. This makes it possible to effectively utilize the luminous flux from the photographic lens, and to prevent the necessary luminous flux from being blocked by the exit pupil of the photographic lens.

In addition, the second condition for ensuring the sameness of the common portion of the light amount distribution formed on the two sensor rows is the interval between corresponding positions of the light amount distribution on the two sensor rows 5-1.5-2. is constant over the entire visual field range in which focus detection is performed.

That is, in FIG. 5, the origin is the optical axis of image points A, A2 on the two sensor arrays 5-1, 5-2, which correspond to the point AO that is y apart from the optical axis on the planned focal plane. Letting the coordinates in the sensor row direction be Yl (y) and Y2 (y), respectively, Z (y) = Y1 (y) Y2 (y)
-(2) is invariant for any y within the field of view. Now, taking y on the vertical axis, the difference between the reference wavelength and the value of 2 when y=Q is △Z (y) = Z (y) −Z (0)...
- If you draw a graph with (3) as the horizontal axis, it will look like the one shown in Figure 8, for example. The solid line shows the characteristics for a standard wavelength of light, such as the d-line, and the broken line shows the characteristics for a different wavelength, such as the g-line. In this figure, if both curves coincide with the vertical axis, it can be said that the interval between corresponding positions of the light amount distribution on the two sensor arrays is constant over the entire visual field range in which focus detection is performed.

When switching the aperture aperture of the focus detection system as shown in FIG. 5, the performance of the focus detection system shown in FIG. 8 must always be maintained in a good state. However, switching the diaphragm aperture means changing the luminous flux used for focus detection, and generally such a thing cannot be expected.

For example, even if a relatively good performance as shown in FIG. 8 can be obtained with the aperture shown in FIG. 7(a), if the aperture is changed to the aperture shown in FIG. 7(b), In addition, when the aperture aperture is changed to that shown in FIG. 7(c), the 10th
As shown in the figure, the above-mentioned performance changes and the focus detection accuracy decreases. In particular, as shown in FIG. 7, the distance between the centers of gravity of the two diaphragm apertures is different for each state, L2. In the case of a difference such as L3, this change becomes remarkable.

In this way, it is extremely difficult to switch and use a plurality of apertures with different aperture shapes for one focus detection system and to always maintain focus detection accuracy.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems and prevent a decrease in focus detection accuracy caused by switching the aperture without requiring a new detection means for detecting the position of the aperture. An object of the present invention is to provide a focus detection device that can perform the following functions.

(Features of the Invention) In order to achieve the above object, the present invention provides a sensor using one parameter related to the amount of deviation of the center of gravity of the aperture from the normal position that occurs when the aperture shape of the aperture is changed by the aperture control means. A correction conversion means for correcting and converting the signal output, and detecting the relative positional relationship of a pair of light quantity distributions from the correction conversion signal from the correction conversion means, and based on the correction conversion signal obtained from the determined parameters. correlation calculation means for performing focus detection, and at least three different
and a parameter determining means for determining the value of one parameter from the result of the correlation calculation means obtained for the values of the two parameters, and by correcting and converting the sensor signal output according to the parameter, the aperture can be adjusted. The present invention is characterized in that the amount of deviation of the center of gravity of the aperture from the normal position that occurs when the aperture shape changes is corrected.

(Embodiments of the Invention) Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 1 is a diagram showing the basic configuration of a focus detection device that is an embodiment of the present invention, and parts common to the focus detection system in FIG. 5 are given the same reference numerals. However, here the aperture is 6
Assume that the shape of the pair of openings is variable as shown in FIG. 7, for example.

In FIG. 1, reference numeral 60 denotes an aperture control means for varying the aperture 6 in accordance with the lens used. Specific methods for realizing this include, for example, as shown in FIG. 2, a method of moving the diaphragm 6 having a plurality of pairs of apertures with different shapes in the direction of arrow 71 in the same figure, and One possible method is to configure the diaphragm 6 with an element that can electrically change the transmission state of light. Reference numeral 61 denotes a correction conversion means for receiving a signal output from the sensor 5 and correcting and converting the distortion of the light quantity distribution. Reference numeral 62 denotes a correlation calculating means for receiving the corrected and converted signal and detecting the relative positional relationship thereof.

In the above configuration, the aperture control means 60 changes the aperture shape of the aperture in response to an external signal, and sends information regarding the aperture shape of the selected aperture 6 to the correction conversion means 61. The object of the present invention is achieved by the correction conversion means 61 changing or selecting the correction conversion method according to the information from the aperture control means 60. As mentioned above, the most important piece of information regarding the aperture shape of the diaphragm 6 is the distance between the centers of gravity of the apertures. Note that it is also possible to adopt a configuration in which only one sensor output is corrected and converted to match the distortion state of the other sensor.

Next, a specific calculation method of the correction means 61 will be explained.

The most common correction method uses the output of the nth pixel of the sensor before correction as a. When , the output of the m-th sensor after correction is used as a coefficient of 7, = Σknan
−(4) and linear transformation. However, the amount of distortion in the actual secondary optical system is not so large, and the output after correction conversion of one pixel is
It is considered that it depends only on the output of the pixel, so bs”
kn-+ an-+ + kn tan ""
(5) Or, bm = k n-+ a n-1+ k n
an + kn meeting + a nil... (6
) is sufficient. Here, when the amount of distortion aberration is not large, m=n or m=n-1 holds true. The coefficient kn is a function of distortion determined by the shape of the secondary optical system and the aperture aperture. The correction conversion means 61 has a memory section that holds these coefficients, and reads out necessary coefficients and performs correction conversion in response to switching of the aperture 6.

Next, the relationship between specific coefficients and distortion will be explained.

FIG. 3 is a diagram showing only the principal ray of the light flux related to the first light amount distribution of the focus detection system of FIG. 1. In this diagram,
A coordinate axis X is set on the sensor row 5-1 in the row direction, and a coordinate axis X is set on the predetermined focal plane 7 in the visual field direction. However, both coordinate axes x,
It is assumed that the origins of X correspond optically. That is, it is assumed that the chief ray emitted from x=o reaches the point X=○ on the sensor array. Using this coordinate system, the image formed by the secondary imaging system has a distortion aberration h (x)X100%, so that X=
βo x (1+h (x) )
--Assume that they are related by (7). However, β. is a reference horizontal magnification, for example, the magnification when x=O.

For boat fishing, the distortion aberration H(X) and the lateral magnification β are based on the coordinate X on the planned focal plane 7. Although it is normal to consider the formula % formula % (8) using
We will use the formula. The above formulas (7) and (8) indicate the same content, and there is no theoretical difference.

Now, the amount of light on the sensor 5 is g (x), and the planned focal plane 7
If the above light intensity distribution (the light intensity distribution due only to the light flux forming the light intensity distribution g (x)) is f (x), then if there is no loss in light intensity, there will be g (x)dx=f (X
)dx...There is the relationship shown in (9). Therefore (
7) From formula, assuming that the variation of h (x) due to X is sufficiently small, dx = [βo x (1+h (x)) + βo'
X (1+h (x) )] dx=βo x
(1+h (x))dx... (10) Therefore, the above equation (9) is g (x)dx=f (β.x (1+h (x))
)×βo (1+h (x) ) (11) If u7 sensor bit, which is the coordinate of the center of the n-th pixel in the sensor row, is P, then the output a of the n-th pixel. is g (x
) is sufficiently small within the sensor pitch, =g (un') P...
・(12) Furthermore, from equation (11), an=f(βoun (1+h(un')))×
βo (1+h (url') ) P where un=βo un (1+ h (un'
)... (15) Then A, = f (uo)P73o - (16
) On the other hand, the m-th value that should be obtained when there is no distortion
The output B of the th pixel is f(u ′βo) pβQ = f(vs) pβ0 (17) where V sa ” um β0 Therefore url−, <v, ′≦uI.

Interpolation is performed for n that satisfies... (18) ... (19) ... (20). As shown in Fig. 4, the above equation (20) gives the output B to be determined using the two values u closest to v,'.
−+ l u n is obtained by performing linear interpolation from the output value, and corresponds to the case where the two coefficients shown in the above equation (5) are included. In addition, a known interpolation method may be used as appropriate, such as calculating a certain function by the least squares method using the outputs at the three points closest to ■, and performing interpolation.

Assuming that a coordinate axis X' similar to X is defined on the sensor row 5-2 regarding the second light intensity distribution, and the distortion is i(X), in the above equation, X is X and h (x) is i ( x
' ), a correction conversion formula can be derived. Due to the symmetry of both light quantity distributions, h (x) = i (-x) - (20) holds if there is no manufacturing error. Furthermore, it is also possible to correct and transform only one of the two light quantity distributions to match the distortion of the other. For example, in order to correct and transform only the first light amount distribution, h (x) in the previous equations may be replaced with h (x) −i (x).

h (x) and i (x') representing the above-mentioned distortion can be determined as design values. Further, by using values measured for each focus detection system, correction that takes manufacturing errors into account can be achieved.

According to this embodiment, the correction conversion means 61 selects a correction coefficient suitable for the information on the aperture shape sent from the aperture control means 60 from an internal memory section held in advance, and uses the correction coefficient. Correcting and converting the signal output from sensor 5,
The correlation calculation means 62 that receives this correction conversion signal is configured to detect the relative positional relationship between the pair of light quantity distributions based on the correction conversion signal and perform focus detection, so the position of the aperture is detected. This solves the problem of a decrease in focus detection accuracy caused by switching the aperture, without requiring a new detection means for the purpose of the diaphragm, and enables optimal focus detection no matter what brightness of the lens is used. becomes possible.

(Effects of the Invention) As explained above, according to the present invention, the sensor is controlled by one parameter related to the amount of deviation of the center of gravity of the aperture from the normal position, which occurs when the aperture shape of the aperture is changed by the aperture control means. A correction conversion means for correcting and converting the signal output, and detecting the relative positional relationship of a pair of light quantity distributions from the correction conversion signal from the correction conversion means, and based on the correction conversion signal obtained from the determined parameters. correlation calculation means for performing focus detection, and at least three different
and a parameter determining means for determining the value of one parameter from the result of the correlation calculation means obtained for the values of the two parameters, and by correcting and converting the sensor signal output according to the parameter, the aperture can be adjusted. Since the shift amount of the center of gravity of the aperture from the normal position that occurs when the aperture shape changes is corrected, there is no need for a new detection means to detect the position of the aperture. It becomes possible to prevent a decrease in detection accuracy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of a focus detection device in an embodiment of the present invention, FIG. 2 is a diagram showing a configuration of the diaphragm shown in FIG. 1, and FIG. 3 is related to one light amount distribution in this embodiment. FIG. 4 is a diagram showing the principal ray of the luminous flux, FIG. 4 is a diagram also explaining interpolation, FIG. 5 is a diagram showing a conventional focus detection system, and FIG.
Figures a) to (d) are diagrams showing cross sections of the objective lens on the exit pupil plane, and Figures 7 (a) to (C) are diagrams showing the sizes of aperture apertures selected corresponding to lenses of different brightness. Fig. 8A is a diagram showing the case where the pair of light intensity distribution curves over the entire viewing range is appropriate, and Figs. It is a figure which shows the case where it disappears. 2...Field mask, 3...Field lens, 4...Secondary optical system, 5...Sensor, 6...Aperture, 60... Aperture control means, 61... Correction conversion means, 62...
・Correlation calculation means.

Claims (1)

[Claims] (1) A secondary optical system for forming at least one pair of light intensity distributions using light fluxes from different regions of the pupil of the objective lens, and a variable-shape aperture for limiting the light flux that passes through the secondary optical system. A focus detection device comprising: a diaphragm having a diaphragm; a diaphragm control means for changing the aperture shape of the diaphragm; and a sensor for detecting a light amount distribution formed by the secondary optical system and extracting it as a signal output, 1 related to the amount of deviation of the center of gravity of the aperture from the normal position, which occurs when the aperture shape of the aperture is changed by the aperture control means.
a correction conversion means for correcting and converting the sensor signal output using two parameters; Correlation calculation means for performing focus detection based on a correction conversion signal, and parameter determination means for determining the value of one parameter from the results of the correlation calculation means obtained for at least three different values of the parameter. A focus detection device characterized by: