JPH0456813A - Focus detector - Google Patents

Abstract

PURPOSE:To make a detecting means for detecting the position of a diaphragm unnecessary 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 its centroid position which is at the time of changing the aperture shape of the diaphragm. CONSTITUTION:The focus detector is provided with a correcting/converting means 61 for correcting/converting a sensor signal output by a parameter related to the deviation of the aperture from the normal position of the centroid position which is generated when the aperture shape of the diaphragm is changed by a diaphragm control means, a correlation arithmetic means 62 for detecting a focus based upon a correction/conversion signal found out by the determined parameter and a parameter determining means 63. Thereby, the deviation of the aperture from the normal position of the centroid position which is generated when the aperture shape of the diaphragm is changed. Consequently, a new detecting means for detecting the position of the diaphragm is not required and 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 l 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 method will be briefly explained below.

The outputs photoelectrically converted by the two sensor rows 5-1 and 5-2 are respectively a(i) and b(i) (where i
= 1 to N, where N is the number of pixels of one sensor), then for an appropriate constant integer k, V(m) = Σmin (a(i), b (-m to i+)) - Σmin (a (i+k), b
(i − m) )...(1) is calculated for different integers m. However, m1n(A,
B) is a function that extracts the smaller one from A and B. The range of i to calculate the sum is -m, i for each subscript i, i+
+, i+m falls in the closed interval [1, N], and the fluctuation range of i in the first term and the second term of V (m) is determined to be equal.

Figure 6 shows an example of the change in V (m) with m, and the value of m at which V (m) becomes rOJ is 1 of the sensor.
This is the amount of deviation between the two light amount distributions when pitch (pixel) is used as a unit. Normally, V (m) is not necessarily "○" for an integer m, but in such a case, a fractional value can be obtained using an appropriate interpolation method. The simplest interpolation method is linear interpolation, where V (m o ) and V (mo
+ 1 ), the deviation amount M including the fraction is calculated as follows (2).

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 in this way is to use the proportionality constant K, assuming that both are approximately proportional, and calculate d=-M ・...It is obtained by (3). In addition, the present applicant has also proposed a calculation method that improves this formula and takes into account the nonlinearity between d and M.
Although it is disclosed in No. 107311, 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. 7 shows a cross section of the objective lens 1 in FIG. 5 on the exit pupil 7 plane.

In FIG. 7(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, 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. 7(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. 7(C), the entrance pupil 9-1, 9-2 of the focus detection system is not completely included in the exit pupil lO of the objective lens 1, but the blocked 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. 7 (
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. 7(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 size of the aperture of the aperture of the focus detection system is made variable in accordance with the brightness of the photographing lens. For example, all photographic lenses that should be usable are categorized into three types based on their 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. 8(a), 8(b), and 8(c) 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.

Now, in Fig. 5, a coordinate axis X whose origin is the intersection with the optical axis is taken on the planned focal plane, and
At the top, coordinate axes x and x' are taken in the column direction, respectively. however,
It is assumed that the origins of both coordinate axes x and x' correspond optically to the origin of coordinate axis X. That is, it is assumed that the chief ray emitted from X=○ reaches the points x=O and x=O on each sensor row 5-1, 5-2. Using this coordinate system, the image formation by the lens 4-1.4-2 of the secondary thread has a distortion aberration E (
X)X100% and E' (X)X100%, x (X)=XBo (1+E (X)) −(4
)x (X)=Xβo (1+E' (X)
), then the second condition above is Δx (X
)=x (X) -x (X) ...(6) is always "0" for any X within the field of view of the planned imaging plane
It is to be. However, here, β0β0' is the reference X, for example, the imaging magnification at x=O. In addition, if there are no manufacturing errors, β0 = β0 due to the symmetry of the system (7) E
(X)=E" (-X) ... (8)
holds true. Therefore, equation (6) is △x (X) = Xβ. (E (X)-E' (X))
=Xβ. (E (X) -E (-X) )...(9
) becomes. If the above equation (9) is drawn on a graph with the X axis on the vertical axis and ΔX on the horizontal axis, it will look like the one shown in FIG. 9, for example.

The solid line indicates the characteristics for the reference wavelength of light, for example, the d-line,
The broken lines each indicate the characteristics for a different wavelength, for example, 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 diaphragm aperture of the focus detection system mentioned above, it is especially important that the relative positional relationship between the secondary optical system and the diaphragm aperture arranged correspondingly remains constant. It is not always easy to meet these requirements. In particular, when changing the aperture by mechanically moving the aperture member, it is necessary to increase the driving accuracy and to detect the position of the aperture. Very difficult to achieve.

Figure 10 shows the state in which the relative positional relationship between the three apertures has changed during the process of switching between the three apertures as shown in Figure 8 (a).
) is shown as an example. Figure 10(a)
10(b) shows a state in which the aperture of the diaphragm is shifted in the left-right direction with respect to the secondary optical system 57, and FIG.
7, respectively, are shown shifted in the vertical direction. If the diaphragm aperture is shifted vertically as shown in Fig. 10(b), the performance of the focus detection system shown in Fig. 9 does not change significantly, but as shown in Fig. 10(a), the diaphragm aperture shifts left and right. If it deviates, the curve will be in a tilted state as shown in FIG. 11, and the focus detection accuracy will deteriorate.

In a certain limited range, there is a proportional relationship between the amount of left and right deviation of the diaphragm aperture and the slope of the curve. The aforementioned coordinate system
, x, x' and the slope of the curve is S, the above (9
) From the formula, S=βO(E (X) −E ' (X) )−(1
0). That is, a change in the slope S of the curve means that the difference in distortion between the two images changes in proportion to it.

Figure 12 shows the above (1) when the slope of the curve in Figure 9 changes.
) The change in V(m) due to m shown in the formula is V(m)=
The figure shows the vicinity of O.

In the figure, 81 indicates a case where the curve has no slope, 82 indicates a case where the curve has a positive slope, and 83 indicates a case where the curve has a negative slope. As shown in the figure, when the curve is tilted, the focus detection system calculates the in-focus point position M2 and M.
, deviates from the normal in-focus position M1 when there is no tilt, making it impossible to perform accurate focus detection.
Since the identity of the two light quantity distributions is impaired, a sufficient correlation cannot be established, and the slope when V(m) intersects the horizontal axis is smaller than in the normal case.

(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 the light amount distribution from the correction conversion signal from the correction conversion means, and detecting the focus based on the correction conversion signal obtained from the determined parameters. and parameter determining means that determines the value of one parameter from the results of the correlation calculation means obtained for at least three different values of the parameters, and the sensor signal is determined by the parameter. The present invention is characterized in that by correcting and converting the output, the amount of deviation of the center of gravity of the aperture from the normal position that occurs when the aperture shape of the diaphragm 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 which is an embodiment of the present invention, and parts common to the focus detection system of FIG. 5 are given the same reference numerals. However, it is assumed here that the diaphragm 6 is constructed such that the shape of its pair of openings is variable, as shown in FIG. 8, for example.

In FIG. 1, reference numeral 60 denotes an aperture control means for varying the aperture 6 in accordance with the lens used. As a specific method for realizing this, for example, as shown in FIG. 2, a method of moving the diaphragm 6 having a plurality of aperture pairs of different shapes in the direction of the arrow 71 in the same figure can be considered. 6
1 is a correction conversion means 62 that receives a signal output from the sensor 5 and changes the amount of distortion of the light amount distribution contained therein;
receives the corrected and converted signal, detects its relative positional relationship, and performs a correlation calculation based on the corrected converted signal determined by the parameters determined by the parameter determining means described later to perform focus detection. calculation means, 63
is a parameter determining means for determining parameters necessary for the correction conversion of the correction conversion means 61.

Here, the correction conversion by the correction conversion means 61 may be performed on the signals from each of the two sensor rows 5-1 and 5-2, as will be described later, or may be performed on the signals from only one of the sensor rows. It's okay.

In the above configuration, the diaphragm control means 60 changes the diaphragm aperture shape as shown in FIG. 8, for example, in response to an external signal. When the parameter determination means 63 detects that the aperture shape has changed, it sends one parameter t associated with the amount of deviation of the center of gravity of the aperture from the normal position to the correction conversion means 61. 61 uses this parameter t to correct and convert the sensor output by a method described later. The correlation calculation means 62 uses the corrected and converted sensor output value to calculate the above (
1) Perform calculations regarding relative positional relationships such as V (m) in the equation. The above series of operations is performed for at least three different predetermined parameters t, and the parameter determining means 63 temporarily stores the results. As this parameter t, the amount of deviation of the center of gravity of the diaphragm aperture from the normal position may be used, but for later calculations, it is better to use a value that corresponds to the difference in distortion included in the two light intensity distributions. , these are quantities proportional to each other, as mentioned above. Specifically, if ±b is the difference in distortion corresponding to the maximum deviation of the center of gravity position of the diaphragm aperture from the normal position, which is determined by the driving accuracy of the diaphragm control means 61, the three of O and ±b can be expressed as the parameter t. The above calculation is performed on the value of .

Next, the parameter determining means 63 determines, based on the obtained results, that the difference in distortion caused by the deviation of the center of gravity of the actual diaphragm aperture from the normal position, that is, the correction conversion means 61 is necessary to perform accurate focus detection. The parameter t. is predicted and determined as follows.

To do this, if the difference in distortion changes due to a shift in the center of gravity of the aperture, it becomes difficult to correlate the two light intensity distributions, and the slope when V (m) intersects the horizontal axis in Figure 12 is Take advantage of being smaller.

In FIG. 3, the horizontal axis is the parameter t, and the vertical axis is the slope when V(m) obtained for these intersects the horizontal axis. In this figure, the parameter t0 is determined by interpolating the value of t that gives the maximum value that gives the largest slope. As an interpolation method, 3
A known interpolation method is used, such as a method for determining the center of gravity of two values or a method using the least squares method. Also, in the explanation so far, the number of parameters t with different values has been three, but four
It is also possible to have more than one, and the interpolation method can be selected optimally depending on the number.

Determination of the above parameter to can always be performed with high accuracy in focus detection by determining the parameter to every time distance measurement calculation is performed. However, in order to shorten calculation time, it is necessary to determine the parameter to immediately after turning on the camera power or immediately after switching the aperture aperture. The parameter t0 may be determined only prior to the first distance measurement, and the same parameter may be used thereafter until the aperture aperture is newly switched.

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

The most common correction method is that when the output of the n-th pixel of the sensor before correction is an, the output of the m-th sensor after correction is expressed as a coefficient k. is used, =Σkn an
−(11) and performs a 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 thought that it depends only on the output of 3 pixels, so ba ”
kn-r an-+ + kn an ”” (
12) Or bag = kn-1a n-1+ kn an
It is sufficient to use a conversion formula such as +knit a n*+... (13). Here, if the amount of distortion is not large, m=n or m=n-1 holds true. The above coefficient k. is a function of distortion determined by the shape of the secondary optical system and the aperture, and can be derived theoretically under certain assumptions.

First, the relationship between X and X' is derived from equations (4) and (5) above... (14) Here, β. =β. ', and if E(X) and E''(X) are sufficiently small, then x = x [1-(E (X) E'' (X) )
] m = (1-t) ... (15) However, from the above formula (l○), since the slope of the curve in Fig. 11 is constant regardless of X, using the constant t, E(X)- E'(
X)=t-(16). This t is the above-mentioned parameter.

Now, when the light intensity distribution of the first image is g (x) and the light intensity distribution of the second image is f (x"), if the light intensity is equal, there will be g (x) dx = f ( x")dx" (17). Therefore, from equation (15), dx'= (1-t)dx = (18) Therefore, equation (17) above is g (x) dx=f (x (1 -t) )(1-t
)dx-(19) Let U be the coordinates of the center of the n-th pixel of the sensor array that detects the light intensity distribution of the first image. , the sensor pitch is P, then the nth
Output a of the th pixel. Assuming that the change in g(x) is sufficiently small within the sensor pitch, =g(un”)P
... (20) Furthermore, from equation (19), an = f(un ” (1-t) ) (1-
t) P...(21) Here an A・"1- t -(22) un
”un (1j)...
(23), then A, = f (un)P - (2
4) On the other hand, when it is assumed that a light quantity distribution is formed on the first sensor row with the same distortion as the second light quantity distribution, the output B of the m-th pixel that should be obtained from the first sensor,
= f (u, ') P...
(25) Therefore, interpolation is performed for n that satisfies u, -1<uwa ''≦un... (26) ... (27) The above equation (27) is as shown in Figure 4. The two values U closest to u,′ that give the output B to be obtained for .−1
, u, and corresponds to the case where the two coefficients shown in equation (12) above are included. In addition to this, for example, U.

A known interpolation method can be used as appropriate, such as finding a certain function by the least squares method using the outputs at the three points closest to , and performing interpolation.

The above describes the case where only the first image of the two light intensity distributions is corrected and converted, but when only the light intensity distribution of the second image is corrected and converted, instead of the above equation (15), x= x' (1+t) ... (28)
Then, in the above formulas, X can be replaced with X' and t can be replaced with -t. It is also possible to perform correction conversion on both of the two light amount distributions, in which case t may be replaced with t/2 in each conversion formula.

According to this embodiment, the 1
The signal output from the sensor is corrected and converted using two parameters to create this corrected conversion signal.

Detect the relative positional relationship between a pair of light intensity distributions, obtain such relative positional relationship for at least three different parameter values, and determine the value of one parameter from the results of these correlation calculations. Since focus detection is performed by performing a correlation calculation using a signal that has been corrected and converted based on this parameter, there is no need for a new detection means to detect the position of the aperture, and it is possible to switch the aperture. This solves the problem of the accompanying decrease in focus detection accuracy, and makes it possible to perform optimal focus detection no matter what brightness of the lens is used.

(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 the light amount distribution from the correction conversion signal from the correction conversion means, and detecting the focus based on the correction conversion signal obtained from the determined parameters. and parameter determining means that determines the value of one parameter from the results of the correlation calculation means obtained for at least three different values of the parameters, and the sensor signal is determined by the parameter. By correcting and converting the output, 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 changes is corrected, so a new detection means for detecting the aperture position is not required. Therefore, it is possible to prevent the focus detection accuracy from decreasing due to the switching of the aperture.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of a focus detection device according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration of the aperture shown in FIG. 1, and FIG. 3 is a diagram explaining the determination of parameters in this embodiment Figure 4 is a diagram also explaining interpolation,
Fig. 5 shows a conventional focus detection system, Fig. 6 shows an example of the sensor output, and Figs. 7 (a) to (d) show cross sections of the objective lens on the exit pupil plane. Figure, Figure 8 (
a) to (C) are diagrams showing the size of the aperture aperture selected corresponding to lenses of different brightness, and Figure 9 similarly shows the case where a pair of light intensity distribution curves over the entire viewing range is appropriate. Figure 10 is a diagram showing the case where a positional shift occurs between the secondary optical system and the aperture, and Figure 11 is a diagram showing the case where the pair of light intensity distribution curves in Figure 9 are no longer appropriate. , FIG. 12 is a diagram showing the sensor output state in the states shown in FIGS. 9 to 11. 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, 63...Parameter determination means. Figure 3 Figure 4

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; and detecting the relative positional relationship of the light quantity distribution from the correction conversion signal from the correction conversion means;
Correlation calculation means for performing focus detection based on a corrected conversion signal obtained by the determined parameter, and determining the value of one parameter from the results of the correlation calculation means obtained for at least three different values of the parameter. What is claimed is: 1. A focus detection device comprising: parameter determining means.