JPS626206B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in automatic focus detection devices. 2. Description of the Related Art Conventionally, an automatic focus detection device in an autofocus device of a camera has a dual image matching distance measuring method. In this method, as shown in FIG. 1, the exit pupil 12 of the objective lens 11 is divided by a pupil splitting optical system 10, and the imaging action light rays of the objective lens 11 that pass through parts 12A and 12B of the exit pupil 12 are grouped into A groups. optical sensor SA _p …SA _i …SA _o and optical sensor SB _p … of group B
SB _i ...incident corresponding to SB _o . These optical sensors are paired with SA _p and SB _p , SA _i and SB _i , SA _o and SB _o, respectively, and these two optical sensors have the same location on the focus detection surface. Of the light beams incident on the image forming apparatus, the imaging effect light beams passing through the portions 12A and 12B are incident thereon. As shown in FIG. 2, when the photographic lens is out of focus from the subject, a phase difference occurs between the outputs of the paired optical sensors. Moreover, the position of the output phase shift of the A group and B group of the optical sensor is reversed due to the front and rear focusing. Furthermore, when comparing the outputs of the optical sensors at time T _p and time T _t , the directions of the output phase shifts of the A group and B group of the optical sensors with respect to focusing are always opposite to each other. For example, the arrow 〓 indicates the direction in which the output phases of the A group and the B group of the optical sensor are shifted when focusing on the front focus position and the rear focus position. FIG. 3 shows the illuminance of the subject on the focus detection plane, where A is when the subject is in focus, B is when the front is in focus, and C is when the subject is in rear focus. Such a group of optical sensors SA _p ~
Double image matching distance measurement is performed from the outputs of SA _o and SB _p to SB _o . Here, the optical sensor group SA _p ~ SA _o , SB _p
As shown in Fig. 4, only one type of SB _o is arranged in each element 9, and a pair of Optical sensors SA _p and SB _p ,…SA _o
The spacing d and shape of and SB _o are matched to a lens with a relatively large open aperture value, for example, an F4 lens as shown in FIG. However, in such an automatic focus detection device, since the distance d between the optical sensors is small, the baseline length D for double image matching distance measurement cannot be set very large.
The distance measurement accuracy is poor. For this reason, the opening aperture value is small.
For example, if you attach a lens such as F1.4 to a camera, it will not focus well. When the aperture value exceeds a certain value (F4 or higher in Figure 5), no light reaches the optical sensor, making distance measurement impossible. The above-mentioned problem is a trade-off as it stands; improving distance measurement accuracy will reduce the number of lenses that can be used, and conversely, increasing the number of lenses that can be used will worsen distance measurement accuracy. SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focus detection device that can sufficiently expand the range of usable open aperture values while maintaining sufficient distance measurement accuracy for lenses with various open aperture values. . Embodiments of the present invention will be described below with reference to the drawings. This embodiment uses 1 in the above automatic focus detection device.
The paired optical sensor groups SA _p ~SA _o , SB _p ~ _{SB o} can be changed from the conventional one type to multiple types _SA1p ~ _SA1o , as shown in Fig. 6.
SB _1p ~ SB _1o , SA _2p ~ SA _2o , SB _2p ~ SB _2o , SA _3p ~
SA _3o , SB _3p to _{SB 3o} are selected, and one type of optical sensor group most suitable for the open aperture value of the lens attached to the camera is selected, and distance measurement is performed based on its output. When a lens of F1.4 to 2 is attached to the camera, the imaging action light beam of the lens is divided into pupils by the pupil division optical system 10 and sent to the first row of photosensor groups SA _1p to SA _1o , SB _1p to If a lens of F2.8 to ₄ is attached to the camera, the imaging action light beam of that lens is divided into pupils by the pupil division optical system 10 and sent to the second row of photosensor groups SA _2p to SA. _2o ,
SB _1p to SB _2o , and if a lens of F5.6 to 8 is attached to the camera, the image-forming light of that lens is split into a pupil by a pupil splitting optical system 10 and sent to the third row of photosensors. Receive at SA _3p ~ SA _3o , SB _3p ~ _{SB 3o} . Three rows of optical sensor groups SA _1p ~ SA _3o , SB _1p ~
SB _3o is constructed on one element 13 and is driven by a photosensor drive circuit 14 as shown in FIG.
A maximum aperture value pin is attached to the lens, and a detection means for detecting the pin and generating a lens maximum aperture value signal is provided on the camera side. The multiplexer 8 selects the output of the optical sensor group in the row corresponding to the lens according to the lens open aperture value signal, i.e.
For F1.4-2 lenses, the first row of optical sensors
SA _1p ~ _{SA 1o} , SB _1p ~ _{SB 1o} output A _1p ~ _{A 1o} , B _1p
~B _1o is selected, and for the F2.8 ~ 4 lens, the output A ₂ of the second row of photosensor groups SA _2p ~SA _2o , SB _2p ~ _{SB 2o}
Select _p ~ A _2o , B _2p ~ B _2o , and for F5.6 ~ 8 lenses, select the third row of photosensor groups SA _3p ~ SA _3o , SB _3p ~
Select the outputs A _3p to A _3o and B _3p to _{B 3o} of SB _3o .
The outputs of this multiplexer 8 A _p ~A _o , B _p ~B _o
is converted into a digital signal by an A/D converter 16 via a video amplifier 15 and stored in memories 17 and 1.
8 is stored. In this case, the memory 17 stores the signals A _p to A _o from the A group of optical sensors, and at the same time the memory 18 stores the signals from the B group of optical sensors. The output signal of this memory 18 is shifted by a shift circuit 19 and sent to the memory 17 by a differential circuit 20.
The difference between the opposing signals from is taken. The absolute value of the output signal of the differential circuit 20 is taken by an absolute value conversion circuit 21, and the sum is taken by an integration circuit 22. The control circuit 23 changes the shift amount j of the shift circuit 19 and resets the integration circuit 22 to repeat the above calculation, and uses the memory 24 to find the value k of j when X is the minimum, and adjusts the focus of the photographing lens. Detect conditions. That is, as shown in the flowchart of FIG. 8, first, in steps (1) to (5), data A _p ~A _o , B _p ~ are sent from the element 13.
Read B _o into memories 17 and 18. Next, in steps (6) to (11) The calculation is performed as described above. However, o<a<b<na a≦i≦b bn≦j≦a. This calculation result X is a function X(j) of shift amount j
Thus, the front focus, in-focus, and rear focus shown in FIG. 9 occur. Therefore, the relationship between the value k of j that minimizes X(j) and the focus state of the photographing lens is

[Table] becomes. Therefore, in steps (12) to (18), initially (when j = bn), X is regarded as the minimum value X _MIN and stored in the memory 24, and j = bn is stored in the memory 24 as k. Increment the shift amount j and return to step (7), and from the second time onwards (j≠b
-n), the calculation result X is the minimum value X in the memory 24.
If it is smaller than _MIN , change X _MIN ,k in the memory 24 to that X,j, increment j, and return to step (7); if X _MIN >X, return to step (7). Here, the relationship between the data A _p to A _o and B _p to _{B o} in the memories 17 and 18, the shift amount j, and the range in which the calculation of the above equation (1) is performed is as shown in FIG. And when j=a, step (19) ~
(23), the control circuit 23
From k in 4, the distance is measured by making a judgment using equation (2), and the output drives the lens extension motor to perform focusing, or the detection output displays the focusing status on the display and allows manual operation. Focusing is performed in FIG. 11 shows another embodiment of the present invention. In this embodiment, the lens open aperture value signal is input to the control circuit 23 in the above embodiment, and the control circuit 23 outputs the photosensor selection signal to the multiplexer 8 to select the photosensor output. FIG. 12 shows yet another embodiment of the invention. This embodiment is an example in which the selection of the optical sensor array is performed by a program in the control circuit 23, and in the above-mentioned implementation array, the optical sensor output reading part {steps (1) to (5)} of the calculation program shown in FIG. The contents are changed as shown in FIG. 13, so that among the rows of photosensors on which the light on the element 13 is exposed, the one corresponding to the lens with the smaller open aperture value is selected. In this case, the arithmetic circuit 25

[Formula] The average value of the output of the optical sensor array is calculated, and the control circuit 23 determines whether the optical sensor array is illuminated by light based on whether the average value is greater than or equal to a certain value k. ing. As described above, in the automatic focus detection device according to the present invention, a plurality of types of optical sensors are provided, and one type of optical sensor group is selected and used according to the maximum aperture value of the lens used. Sufficient distance measurement accuracy can be ensured even when using a lens with a small aperture value, and distance measurement is also possible with a lens having a large aperture value. It should be noted that distance measurement accuracy decreases when a lens with a large aperture value is used, but at the same time the depth of field of the lens becomes wider, so there is no problem in practical use.

[Brief explanation of the drawing]

Figures 1A and 1B are schematic diagrams showing part of a conventional automatic focus detection device, Figures 2 and 3 are diagrams for explaining the device, and Figure 4 is a plan view showing the optical sensor of the device. Figure 5 is a diagram for explaining the device,
FIG. 6 is a plan view showing an optical sensor according to an embodiment of the present invention, FIG. 7 is a block diagram showing the same embodiment, FIGS. 8 to 10 are diagrams for explaining the same embodiment, and FIG. 12 and 12 are block diagrams showing other embodiments of the present invention, and FIG.
The figure is a flowchart for explaining the same embodiment. SA _1p ~ SA _3o , SB _1p ~ _{SB 3o} ...Light sensor, 8
...Multiplexer.

Claims (1)

[Claims] 1. In an automatic focus detection device that divides the image-forming light ray of an objective lens into a pupil and receives it by a pair of photosensor groups and detects the focus state from the output signal of this photosensor group, the pair of photosensors are divided into multiple types. Prepare,
An automatic focus detection device characterized in that one type of optical sensor group is selected and used from the plurality of types of optical sensor groups according to the open aperture value of the lens used.