JPS5859416A - Focusing detection - Google Patents

Abstract

PURPOSE:To extend the focusing discrimination display range, by giving an offset of a value, which corresponds to the feed quantity of a photographic optical system, to the calculated value of the evaluation function. CONSTITUTION:The image of an object 1 is led to a light receiving device 3 having a pair of photodetecting element arrays, where many photodetecting elements are arranged, and an optical path dividing prism, which divides and projects the light to these photodetecting element arrays, through a photographic optical system 2, and illuminance information of every photodetector is converted to digital information in parallel by a signal processing circuit 4 and is taken into a central processing unit 5 successively to calculate an evaluation function value. Meanwhile, an offset value corresponding to the feed quantity of the optical system 2 is generated by a means 27 and is subjected to A-D conversion in an A-D converter 28 and is taken into the unit 5 and is given to the evaluation function value for every photodetecting element of the device 3. An obtained focus detection signal is displayed on a device 6, and the optical system 2 is focused through a driving controlling circuit 7 and a driving device 8.

Description

DETAILED DESCRIPTION OF THE INVENTION At least in part, a large number of nine Il! The in-focus state of the optical system is determined by an evaluation function value representing the sharpness of the object image, which is received by a light-receiving array of conversion elements and calculated from a light beam conversion signal of the light-receiving element array according to a predetermined evaluation function. The present invention relates to a focus detection method, and particularly to a focus detection method suitable for use in a focus detection device for a single-lens reflex camera.

FIG. 1 is a block diagram showing the overall configuration of an example of a conventional focus detection device.

The wrinkles of the subject 1 are guided through the photographing optical system to a light receiving device i1J having a pair of light receiving element rows in which a large number of light receiving elements are arranged and an optical path splitting prism for dividing and projecting light onto these light receiving element rows. The illuminance information of each light-receiving element of the light-receiving device 3 is converted into digital information in parallel by the signal processing circuit DA, and then sequentially taken into the central processing unit WtS, where it is arithmetic-processed according to a predetermined evaluation function to obtain an evaluation function value. is calculated to obtain a focus detection signal representing the in-focus state. This focus detection signal is sent to the display device lt4 to inform the photographer of the state of focus, and is also used to adjust the focus of the photographing optical system λ through the optical system drive opening circuit 7 and the optical system drive device l. In the simple type device, the optical system is driven manually by the photographer according to instructions on the display device N6, and the drive control circuit 7 and the driving device W11 are omitted.

The light-receiving device 3 is constituted by, for example, λ light-receiving element rows each consisting of a large number of photoelectric conversion elements, and these light-receiving element rows are arranged at equal distances before and after the planned focal plane of the photographing optical system. For example, when this is applied to an eye reflex camera, the central part of the quick return mirror 10 is placed in the dark optical path between the photographing optical system and the film, as shown in FIG. is a half mirror//, and the photographing light beam reflected by this half mirror/l is guided to an observation optical system comprising a focusing plate 72゜ and a pentaprism 13, while the light beam passing through the 8-7 mirror 11 is guided to a quick return The light beam is guided downward by a reflecting mirror /l provided on the back surface of the mirror IO, and the light beam guided downward is made incident on the optical path splitting prism /1. This optical path splitting prism /3 is provided with a semi-transparent surface /l and a total reflection surface /7 parallel to each other, so that the light transmitted through the semi-transparent surface /6 is incident on one light-receiving confectionery row /I A. , the light-receiving confectionery row with the ability to pass the light beam reflected by the semi-transparent surface /6 through the reflective surface 17 /
IIB. The light-receiving element rows /I A, /nB are arranged at equal positions before and behind a plane that is optically conjugate with the film 9, and these light-receiving confectionery rows /I A, /I B contain images of the same part of the subject. is now projected.

In general, an image of an object formed by an imaging lens exhibits the maximum amount of image when focused. Therefore, if you calculate the image contrast based on the light intensity distribution of the object projected onto the two light-receiving element rows /I A and /l B arranged as above, then the two element rows /g A and /I B ′′ with,
The contrast of the element row near the trench position of the subject l by the photographing optical system λ exhibits a thicker lk value than the contrast of the element row farther away, and the imaging position is both /l and /l.
When it is near the center of B, the pixel Pd/xk, nB
The fun trusts of will be equal.

Therefore, if the central position of the pixel arrays /I A and /I B is set to a predetermined focal plane conjugate to the film plane, the photographic optical It is possible to detect whether or not the house of the subject is imaged on the film surface by the system, that is, whether or not the photographic lens λ is in focus.

Therefore, as described earlier, the light receiving element array/l k
, /IB are alternately guided to the signal processing circuit for each light-receiving element row by control signals from the central processing unit, where they are converted into digital signals and then sequentially taken into the central processing unit. , the element array/l is calculated according to a predetermined evaluation function for evaluating contrast.
Find the evaluation amount Th lli for each A, /l B and calculate 1
．． By comparing these, a focus detection signal is obtained.

FIG. 3 shows the evaluation function values when the evaluation function y or F-machi (M is the maximum absolute value of the difference in the output of light 111E conversion confectionery in an adjacent relationship in the same light-receiving element row). is expressed with the amount of defocus plotted on the horizontal axis.

Let F2 be the evaluation function value of the evaluation function F for the two light receiving element rows/gm#ItB, respectively.If F<F2, then front focus; if F□-F2, focus;
If F engineering > F2, it will be a rear pin. However, as shown in the figure, when the defocus amount increases, the evaluation values for the two light-receiving arrays /Im and /IB become close to each other, and it is determined that the focus is in focus according to a predetermined determination method. happens. That is, even though the subject is not in focus, it may be determined that F-knee is F2 and an erroneous focus signal may be output. Note that this misfocus signal will hereinafter be referred to as a line signal.

Conventionally, in order to avoid the generation of this erroneous signal, as shown in FIG. and δ2 are provided, and determination is made according to the flowchart shown in FIG. 3, thereby generating and displaying a focus detection signal corresponding to the imaging state.

That is, after the start of detection, first, F + F2 is used to determine whether the focus is true or whether the evaluation values for each light-receiving confectionery row overlap at the bottom of the pile of evaluation values.
2L+, and if F engineering + F2 > 2 L, the absolute fllF knee F21 of the difference in evaluation value is minutely determined by δ2
If IF-F21<δ2, the focus is on, and if 1F-721>δ2, roughly calculate the F-knee F2.
If knee F<0, it is determined to be the front bin, and if F knee F2>O, it is determined to be the rear bin. In addition, the comparison result of F engineering + F2 and JL is F engineering + F2 < ko L, and IF any F21 < δl
In this case, it is determined to be a false signal and nothing is displayed or an indication that focus cannot be detected is displayed. Also, even if the comparison result between F + F2 and Co L is F + F2 < Co L, IF - F21 >
If δ, the same processing as in the case of F+F2>L is used to determine whether the image is in focus, the front bin, or the rear bin and displays it.

However, in the conventional method as described above, the evaluation function F
Since the evaluation values are close to each other at the base of the peaks of 1 and F2, it is difficult to compare the evaluation values, so the practical imaging state detection range in the defocus direction is narrow, and it is difficult to compare the evaluation values. There is a drawback that the image state cannot be detected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel focus detection method that compensates for the drawbacks of the conventional methods as described above and expands the focus determination display range.

In other words, the inability to detect focus according to the present invention is achieved by arranging at least a portion of the object image formed by the optical system one after the other at a certain optical distance across a surface that is conjugate to the image forming plane of the optical system. Light is received by a pair of light-receiving element rows made up of a large number of photoelectric conversion elements, and both evaluation function cases obtained by processing the photoelectric conversion signals from the light-receiving element row for each light-receiving element row according to a predetermined evaluation function are compared. In the focusing method of detecting a focusing state by It is characterized by expansion.

In a preferred embodiment of the present invention, the offset is added to the evaluation function value only when the evaluation amount or numerical value is below a predetermined level.

The method of the present invention will be explained in detail below with reference to the drawings.

FIG. 6A is the same as that shown in FIG. 3, and shows the evaluation values Fl and F2 for the light-receiving confectionery row/I A and 1g B according to the conventional method. As for this evaluation (fiF engineering, F2), as explained earlier, the evaluation values are close to each other at the foot of the mountain.

In the method of the present invention, as shown in FIG. Evaluation 1ii F2 is converted to F2+F'2&, which has a slope corresponding to the offset value, and as a result, F and F at the base part become F in F0.
2, a difference corresponding to the offset value is generated even when the distance is 0.2, so that the separation of F and F is made convenient, thereby expanding the imaging state detection range.

In the example shown in Figure B, the offset F'L' is equivalent to the focal position ilP of the photographing lens and has opposite characteristics with respect to the direction in which the photographic lens is extended, corresponding to F□ and F2 in Figure B. t F'2', and Figure 0 shows this as Fl * F2 plus the corresponding offset F' or FS2, F+F', and the change in F2+F'2'. is shown. As is clear from the figure, the offsets F', , F'2 change in response to the eel being ejected from the Sosho optical system, and have opposite changing characteristics.
If 4 is added to each of the corresponding F and F2, the level of each evaluation value on both sides where the defocus precision in the defocus direction becomes large will be greatly different. In addition, separation at the base of F2 is facilitated, and the imaging state detection range can be greatly expanded compared to conventional methods.

In the above embodiment, the focus position of the photographing optical system [
It is necessary to install one position of F', eli'6' for each off-point at P in the same pupil, and if the pupils are different, the position that is determined to be in focus by the method of the present invention is required. but,
Since the focus position may deviate from the correct focus position, it is necessary to take this point into consideration.

Hereinafter, the fourth embodiment of the dragon of the present invention that solves this problem will be described.

In this method, as shown in FIG. 7, the determination level L1, the minute determination level δ, and δ2 are set as in the conventional method. Evaluation for each light-receiving element array /g A, /I B only when the addition fiF of F2 +F2 is less than 2L and the absolute value of the difference between these evaluation values Fle F2 is less than or equal to the minute judgment level δ□ , the offsets F' and F'', which correspond to the amount of extension of the imaging optical system shown in FIG. By adding the tag ', as shown in Figure C, the absolute value of the difference between the evaluation values in Figure A is less than or equal to δ. 4. In this way, F
By comparing the absolute value of the difference between F+F',' and F2+F'2 with δ2, the defocus range where F+F' and F2 values are close, that is, the in-focus state cannot be determined using the conventional method. By applying an offset only to the disabled range, the focus position P will not shift due to the offset, and the focus determination display range can be expanded.

Figure 1 is a flowchart showing the embodiment. In other words, first compare F-work + F2 and KoL, and then
If F2 is larger than 2L or L, compare each evaluation [Fl, absolute ft1lF of the difference between F2 - F21 with the minute judgment level a2, and if IF any 21 < δ2, focus, IF -y , 1 〉δ2, it is roughly F
-F is calculated, and if F knee F2 is 0, the previous bin,
2 In the case of F knee F2〉O, it is determined that it is a rear pin, which is the same as the conventional method, but in this example, as is clear from the same figure, F + F + F is compared by comparing F + F2 and K L.
is larger and IF any21<δ,
Only in the case of 2, each evaluation 1dt Fl e F2 has an off-scene that changes to the opposite characteristic in the defocus direction) F,, Fe plus F +F and F2+F2'
2 11, and compare the absolute difference between the two with the minute judgment level δ, and get lCF + F engineering) - (F2 + li'2'
)l>δ, only if (F+14') −(F2
If the result is smaller than O, it is determined that the end of the front bin is O or more, that it is the rear pin.

In the above embodiment, each pair of light receiving element rows/l
Each #f value function F1 for each of M, /I B
．． Although an offset was added to F2, it is sufficient to add an offset of 4 only to one of the evaluation function lines, for example, F2.
Of course, if the comparison result of 2 is koL>Fwork+F2, then Fwork and F2 may be immediately offset.

In order to carry out the method of the present invention, it is necessary to provide the evaluation function line for the light-receiving element array with an offset for defocusing of the photographing optical system, and therefore it is necessary to obtain information about the extension of the photographing optical system.

FIG. 9 schematically shows the structure of an embodiment for generating off and set voltages for this purpose, with a part of the lens barrel housing the photographing light string removed. In other words, the photographing optical system moves back and forth along the optical axis 1 by the helicoid mechanism when the focus is adjusted by the focus adjustment @/9, and the holding tube n of the photographing optical system at the helipite portion and the focal point are adjusted. The opposing cylindrical surface G of ring 11/9 is arranged so that the resistor n and sliding contact piece 21 are brought into contact with each other to form a potentiometer'Ii! 1 result.

A voltage is applied to the resistor n from, for example, a power source housed in the camera body to correspond to the position of the sliding contact piece n in the optical axis direction, that is, the position of the m-side optical system λ in the defocus direction. If the voltage is extracted through the sliding contact piece λ, the output voltage will be proportional or inversely proportional to the moving position of the photographing optical system, which is moved in the direction of the optical axis by the operation of the focusing ring /q. and change. 1 The offset voltage generating means using such a potentiometer mechanism is connected to the helicoid section 211! and focus adjustment It/? In order to obtain button and shomemeter outputs that change in opposite directions in conjunction with the operation of can. Figure 1θ shows the equivalent electric circuit, and the same parts as in Figure 95 are shown with the same symbols, so 2J, 2? ' is a resistor provided at one place in the helicopter part, and 20.21' is 1! on the focus adjustment ring 19.
! It is a sliding contact piece that moves. In addition, B is a DC power supply, x, x
' is a pressure output terminal (off-cella) Im which changes with mutually opposite polarity.

FIG. 11 is an overall configuration diagram of a focus detection apparatus using the method of the present invention, and the same functional parts as those of the conventional apparatus shown in FIG. 1 are designated by the same reference numerals. 9 and 1
The extension position detection means of the photographing optical system 2 shown and explained in FIG.
, F'2'.

Reference numeral 1 designates a MuD converter for uniformly converting the offset signals F'' and F'2 which are manually inputted in the form of analog signals according to instructions from the central processing unit S. The digitized offsets F'l' and Fi' are taken into the central processing unit j, and the evaluation functions 1-F and F2 for each light-receiving element row of the light-receiving device 3 calculated by the evaluation function according to the conventional method are calculated here. At the same time, according to a predetermined determination routine, offsets F'l' and F'2' corresponding to the protrusion of the imaging optical system are added to F' and F2 according to a predetermined determination routine.

As is clear from the explanation above, the method of the present invention, in the conventional detection method using a predetermined evaluation function, provides an offset of a value to the itching value of the evaluation function according to the position at which the imaging optical system is extended. Therefore, the evaluation function value of the defocus direction corresponding to either the front focus, the rear focus, or a slight focus of the imaging optical system is made to be actively different from the evaluation function of the ability -, and the two values are compared. Therefore, it is possible to compare the zero evaluation function values even in the defocus direction where the two evaluation function values are approximate. Therefore, the method of the present invention has a special effect in that the imaging state can be detected over a wide range in the defocus direction, where the acid formation state cannot be detected using the conventional method.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of an example of a conventional focus detection device, Fig. 2 is a block diagram showing an example of a light receiving device, and Fig. 3 and @1 show a conventional focus detection method. A characteristic diagram of the evaluation function for explanation, FIG. 3 is a flowchart for explaining the conventional method, and FIG.
FIG. 7 is an explanatory diagram of another embodiment of the method of the present invention, FIG. One example is a schematic configuration diagram with a part of the lens barrel removed, Figure 1θ is an equivalent electrical circuit diagram, and Figure @l1 is a block diagram of an example of a focus detection device using the method of the present invention. FIG. 2 is an overall configuration diagram shown in FIG. L...Subject, K...Photographing optical system, 3...Light receiving device, D...Signal processing circuit,! ...Central processing unit, t
...Display device, 7...Optical system drive control U path, l...
・Optical system drive device, /θ...quick return mirror, ll...half mirror, 1/4I...reflection mirror,
ls... Optical path splitting prism, 16... Semi-transparent surface, /7
...Reflecting surface, /I B...Light-receiving element array,
19... Focus adjustment ring, 〃... Helifit mechanism, 〃・
...Optical axis, n...Lens holding tube, 2? , 231・
...Resistor, 2 da...Sliding contact piece, B...DC power supply,
F, Mut...Set-off voltage output terminal, 1...Photographing optical system extension position detection means, 1...A-D converter. Patent applicant No. 1 Lupus Optical Industry Co., Ltd. Figure 8 Figure 4 (00)
(ifL) 77 Orcus Figure 5 Figure 6 (oo)
(Nganode, 7 years old, Ichika Figure 8)

Claims (1)

[Claims] At least a portion of the object image formed by the L optical system is captured by a large number of photoelectrons arranged one after another at a constant optical distance across a surface conjugate to the image formation plane of the optical system. Light is received by a pair of light-receiving element rows consisting of conversion elements, and image formation is performed by comparing both evaluation function values obtained by processing the photoelectric conversion signal from the light-receiving element row for each light-receiving element row according to a predetermined evaluation function. In the focus detection method for detecting the state,
A focus detection method comprising expanding an imaging state detection range by adding an offset corresponding to an amount of extension of the optical system to the evaluation function value for at least one of the light receiving element arrays. 2' The focus detection method according to claim 1, wherein the offset is added to the evaluation function value only when the evaluation function value is below a predetermined level.