JPH0456811A - 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 by a parameter to correct the deviation of an aperture from the normal position by a parameter to correct the deviation of an aperture from the normal position of a centroid position which is generated at the time of changing the aperture state of the diaphragm. CONSTITUTION:The focus detector is provided with a correlation arithmetic means 62 for detecting the relative positional relation of light distribution by a correction conversion signal outputted from a correction converting means 61 and executing focus detection based upon the correction conversion signal from the means 61 which is found out by a parameter determined in relation to the deviation of the aperture from the normal position of the centroid position generated at the time of changing the aperture shape of the diaphragm and a parameter determining means 63. In said constitution, the deviation of the aperture from the normal position of the centroid position which is generated due to a change in the aperture shape of the diaphragm is corrected by correcting and converting a sensor signal output by the parameter. Consequently, a new detecting means for detecting the position of the diaphragm is not required and the focus detecting 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. 6.

In Fig. 6, 1 is an objective lens, 2 is a field mask placed near the planned focal plane of objective lens 1, 3 is 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. 6, when the imaging point of the objective lens 1 is in front of the planned focal plane,
When the light intensity distributions formed on the two sensor arrays 5-1.・5-
The light quantity distributions formed on the two surfaces 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 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(i+
ni-m) )-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 7 shows an example of how V (m) changes with m, and the value of m that makes V (m) “○” is the sensor’s
0, which is the amount of deviation between two light intensity distributions when pitch (pixel) is used as a unit.Normally, V (m) is not necessarily 0 for an integer m, but in such a case, appropriate interpolation is performed. You can use the method to find fractional values. The simplest interpolation method is linear interpolation, where V(mo) and V(mo +
If the sign is reversed between 1 and 1), the amount of deviation M including fractions 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 = K - M -. ...(3
). Incidentally, an arithmetic method that improves this equation and takes into account the nonlinearity between d and M is also disclosed by the present applicant in Japanese Patent Application Laid-open No. 107311/1982, but detailed explanation thereof 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. 8 shows a cross section of the objective lens 1 in FIG. 6 on the exit pupil 7 plane.

In FIG. 8(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. 8(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. 8(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 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. 8 (
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. 6, even if a certain amount of error occurs as shown in FIG. 8(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. 9(a), 9b, and 9c 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. 6, 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' optically correspond to the origin of coordinate axis X. That is, it is assumed that the chief ray coming out from x=0 reaches the points x=O and x=O on each sensor row 5-1, 5-2. Using this coordinate system, the images formed by the lenses 4-1 and 4-2 of the secondary imaging system have distortion aberration E(
X)X100% and E' (X)X100%, x (X)=X(3o (1+E (X)) -(
4)x (X) =Xβo (1+E ”
(X) )...(5) 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 β.

60' is the imaging magnification at reference X, for example, 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 Δx (X)=XBo (E (X) E' (X
))=XβO(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, for example, FIG. 10. 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 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 11 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 9 (a).
) is shown as an example. Figure 11(a)
11(b) shows a state in which the aperture of the diaphragm is shifted in the horizontal 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. 11(b), the performance of the focus detection system shown in Fig. 10 will not change significantly, but as shown in Fig. 11(a), the diaphragm aperture will shift horizontally. If it deviates, the curve will be in an inclined state as shown in FIG. 12, 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. Using the aforementioned coordinate system X, x, x', and assuming that the slope of the curve is S, then from the above equation (9), S=β. (E (X) −E' (x) )−(1
o). 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 13 shows the above (() when the slope of the curve in Figure 10 changes).
1) Change of V(m) according to m shown in formula 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.
3 deviates from the normal in-focus position M1 when there is no inclination, and accurate focus detection cannot be performed. Also, due to distortion, 2
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 pattern member disposed near a planned focal plane of an objective lens, a correction conversion means for correcting and converting a signal output from a sensor, and a correction conversion means for correcting and converting a signal output from a sensor. The relative positional relationship of the light intensity distribution is detected from the correction conversion signal from correlation calculation means for performing focus detection based on the corrected conversion signal from the correction conversion means; and the correlation calculation means obtained for the light amount distribution regarding the pattern member formed on the sensor by a secondary optical system. and a parameter determining means for determining the parameters from the results of the above, and by correcting and converting the sensor signal output using the parameters, 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 The present invention is characterized in that it corrects for.

(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 in FIG. 6 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. 8, for example.

In FIG. 1, 6o is an aperture control means for varying the aperture 6 according to 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;
is a correlation calculation that receives a corrected and converted signal, detects its relative positional relationship, and performs a correlation calculation based on a corrected converted signal determined by parameters determined by the parameter determining means described later to perform focus detection. 63 is a parameter determining means for determining parameters necessary for the correction conversion of the correction conversion means 61, and 64 is a pattern member disposed near the planned focal plane.

Here, the correction conversion by the correction conversion means 61 may be performed on the signals from the two sensor arrays 5-1 and 5-2, as will be described later, or may be performed on only one of them.

As shown in FIG. 3, the pattern member 64 is a plate-like or film-like member having one or more band-like light transmitting parts and non-transparent parts, and is a cloth in the opening of the field mask 2 as shown in FIG. Or it is placed so that it hangs over the left edge. The pattern member 64 is configured so that it is illuminated by external light from the objective lens 1 and its image is projected onto the sensor 5. Illumination by external light may be affected by the brightness distribution of external objects, but in order to prevent this, 6
It is possible to take measures such as providing an illumination system indicated by 5 and turning it on when necessary, or using a light transmitting part of the pattern member 64 as a diffusing surface. Incidentally, the pattern member 64 may be provided as the same member (2') as a part of the field mask 2, as shown in FIG. Moreover, in the form of FIG. 3, the pattern member 6
By configuring the pattern member 4 to be retractable outside the field mask 2, it is possible to increase the field of view length when the pattern member 64 is not required. The widths of the band-shaped light transmitting portions and non-transmitting portions of the pattern member 64 are set so that the image projected onto the sensor 5 by the secondary optical system is formed on a plurality of sensor pixels. This is determined by the correlation calculation means 62 on the pattern member 6.
This is to reduce the so-called phase-in-out phenomenon in which the calculation result changes due to a change in the relative position of the sensor pixel and the projection image when performing calculations on the projection image of No. 4. Furthermore, the occurrence of the same phenomenon can be suppressed by increasing the number of strip patterns.

In the above configuration, the aperture control means 60
In response to an external signal, the aperture shape of the diaphragm is changed to, for example, the ninth
Change as shown in the figure. When the correlation calculation means 62 detects that the opening shape has changed, the correlation calculation means 62 calculates the pattern member 64.
The calculations shown in equations (1) and (2) described above are performed using signals from only the area of the sensor 5 onto which the image of is projected. If the result of equation (2) at that time is M8, this is the relative position of the projected image of the pattern member 64 formed on the sensor 5 by the secondary optical system through the switched aperture 6, or one pitch of the sensor 5. It is a value expressed in units of - Boat fishing includes the influence of deviation from the normal position of the aperture aperture. Next, the calculating means 62 calculates the value M of equation (2) that should be obtained assuming that there is no shift in the position of the aperture aperture. is stored in memory in advance, and the difference between it and that ΔM=Ms Mo...
- Calculate (11) and send it to the parameter determining means 63.

The parameter determining means 63 uses the 6M obtained here,
The parameter t required for the correction conversion is calculated according to the following formula.

ΔM−P””Xp'β. -(12) where P is the pitch of the sensor 5, XP is the coordinate of the center of the pattern member 64 on the planned focal plane, and β. is the magnification of the secondary optical system. As is clear from equation (9), this value t is the difference E in the distortion of the two light quantity distributions that occurs when the aperture 6 is switched
(xp)−E'(xp)・(13
), which corresponds to the slope of the curve in FIG. 12, as described above. Therefore, it is a constant that does not depend on the coordinate Xp on the planned focal plane. The correction conversion means 61 uses the parameter t determined by the parameter determination means 63,
The output of the sensor 5 is corrected and converted using a correction method as described later. The correlation calculating means 62 calculates equations (1) to (3) using the corrected and converted sensor output to obtain the final result necessary for focus adjustment.

Determining the above parameter t every time a distance measurement calculation is performed to ensure accurate focus detection; however, in order to shorten calculation time, the parameter t may be determined immediately after the camera is powered on or immediately after switching the aperture aperture. The parameter t 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 to use a coefficient kn to represent the output of the m-th sensor after correction, where a is the output of the n-th pixel of the sensor before correction, = 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 of one pixel after correction conversion is considered to depend only on the output of two or three adjacent pixels, so t
:) +++ = ni, -, an-1+kn an
・” (12) Or, bag = kn-+ an-+ + kn an +
It is sufficient to use a conversion formula such as knit an++ (13). Here, if the amount of distortion 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 diaphragm 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. = β0', and assuming that E(X) and E'(X) are sufficiently small, x = x [1-(E (X) E' (X) )
] = x (1-t) ... (15) However, from the above formula (l O), since the slope of the curve in Fig. 12 is constant regardless of X, using the constant t, E (X)-
E” (X)=t・(16).

This t is the above-mentioned parameter.

Now, let g (x) be the light intensity distribution of the first image and f (x') be the light intensity distribution of the second image when fishing on a boat.If the light intensity is equal, there will be g (x)dx=f ( x') dx ・= (17
). Therefore, from formula (15), dx = (1-t) dx = - (18) Therefore, the above formula (17) is g (x) dx = f (x (1-t) ) (1-
t)dx-(19) If un is the coordinate of the center of the n-th pixel of the sensor array that detects the light intensity distribution of the first image, and the sensor pitch is P, then the n-th
Output a of the th pixel. Assuming that the change in g (x) is sufficiently small within the sensor pitch, = g (u, ')
P...(20) Furthermore, from equation (19), a, = f ('u, 1' (lt))N-t)P
... (21) Here an ""1-t ... (22) Lio
=u,” (1t) ... (23) then A, =f (un)P - (24)
On the other hand, assuming that a light intensity distribution is formed on the first sensor array with the same distortion as the second light intensity distribution, the output B of the m-th pixel that should be obtained from the first sensor is = f (uaa ') P...
(25) Therefore, interpolation is performed for n that satisfies u, -, <us'≦un - (26), and Bm = (An An-+)
” ”-' An-+un-u6
-H...(27) It becomes. The above equation (27) is calculated using the two values closest to un' that give the desired output B, as shown in Figure 5.
-1+un Linear interpolation is performed from the output value of n, and corresponds to the case including the two coefficients shown in equation (12) above. In addition, any 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 um 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), and in the previous equations, replace X with X' and t with -1. It is also possible to correct and transform both of the two light intensity distributions, In that case, t may be replaced with t/2 in each conversion formula.

According to this embodiment, the amount of deviation of the center of gravity of the aperture from the normal position that occurs when the aperture shape changes;
The position of the diaphragm is detected because the focus is detected by correlation calculation using a signal that has been corrected and converted based on the parameters obtained for the light intensity distribution regarding the pattern member placed near the intended focal plane of the objective lens. 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 described above, according to the present invention, there is provided a pattern member disposed near the planned focal plane of an objective lens, a correction conversion means for correcting and converting a signal output from a sensor, and the correction conversion means. The relative positional relationship of the light intensity distribution is detected from the correction conversion signal from correlation calculation means for performing focus detection based on the corrected conversion signal from the correction conversion means; and the correlation calculation means obtained for the light amount distribution regarding the pattern member formed on the sensor by a secondary optical system. and a parameter determining means for determining the parameters from the results of the above, and by correcting and converting the sensor signal output using the parameters, the deviation of the center of gravity of the aperture from the normal position that occurs when the aperture shape of the diaphragm changes. Since the amount is corrected, there is no need for a new detection means for detecting the position of the aperture, and it is possible to prevent the focus detection accuracy from decreasing due to switching of the aperture.

[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 a diaphragm shown in FIG. 1, and FIG. 3 is a diagram showing the configuration of a pattern member shown in FIG. 1 and a field of view. 4 is a diagram showing a modification of FIG. 3, FIG. 5 is a diagram explaining interpolation in this embodiment, and FIG. 6 is a diagram showing a conventional focus detection system. 7 is a diagram similarly showing an example of the sensor output, FIGS. 8(a) to 8(d) are diagrams similarly showing a cross section on the exit pupil plane of the objective lens,
Figures (a) to (c) are diagrams showing the sizes of the aperture apertures selected corresponding to lenses of different brightness, and Figure 10 is the distribution plane of the amount of light I, which forms a pair over the entire viewing range. Figure 11 shows the case where the lines are appropriate; Figure 12 also shows the case where a positional shift occurs between the secondary optical system and the aperture; Figure 12 shows the case where the light intensity distribution curves forming the pair in Figure 10 are appropriate. Figure 13 is a diagram showing the case where the
FIG. 2 is a diagram showing the sensor output state in the state shown in FIG. 2; 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, 64...Pattern member.

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, A pattern member disposed near the planned focal plane of the objective lens, a correction conversion means for correcting and converting the signal output from the sensor, and a correction conversion signal from the correction conversion means to determine the relative positional relationship of the light amount distribution. Based on the correction conversion signal from the correction conversion means obtained by the parameter determined in relation to the amount of deviation of the center of gravity position of the aperture from the normal position that occurs when the aperture shape of the aperture changes. Correlation calculation means for performing focus detection; and parameter determination means for determining the parameters from the results of the correlation calculation means obtained for the light amount distribution regarding the pattern member formed on the sensor by the secondary optical system. A focus detection device characterized by being provided.