JPH01183631A - Control system for exposure of camera - Google Patents

Abstract

PURPOSE:To control exposure at a stop down value which guarantees range finding accuracy by providing a passive system range finding means which detects distance to a subject to be photographed and a programming part for determining the diaphragm value and a shutter time by second. CONSTITUTION:When a mode changing switch 17 selects a program mode which gives priority to exposure at a step S-1, the data of a program (a) of a program memory 15, which gives priority to exposure, is read out (S-2), and a TV value is determined from a set AV value (S-5) and such value proceeds to an S-4. At the S-4, the distance is measured, and when focusing is carried out (S-5), a releasing is conducted by the determined shutter time by second (S-6). When an AF guarantee AE program (b) is selected, the AF guarantee AE program (b) of the program memory 15 is read out, and the stop down value AV and the shutter time TV by second is determined at S-8 and S-3 from an exposure value EV. Thus, AF accuracy is guaranteed and correct exposure without defocusing is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an exposure control system for a camera equipped with an autofocus (hereinafter referred to as AF) function.

[Prior Art] In general, cameras in recent years are equipped with automatic exposure (hereinafter referred to as AE) control and AF sub-control, and it has become possible to take clear pictures simply by pointing the camera at the subject and pressing the release button. Automatic exposure control in a camera uses a predetermined program to obtain an exposure value determined from the subject brightness based on the output of a photometric sensor installed inside the camera and the sensitivity of a photosensitive medium such as silver halide film. In some cases, the aperture value and shutter speed are determined according to the aperture value, or an aperture priority program is used that allows the photographer to set the aperture value as desired.

Further, in AF sub-control, for example, in a negative-eye reflex camera, a phase difference detection method is often used in which the AF sensor detects object light obtained through a photographic lens and controls driving of a focusing lens.

[Problems to be Solved by the Invention] By the way, in the case of cameras using silver halide film, the permissible circle of confusion is generally set to about 35μ, so
For example, when a photographic lens of Fl, 2 is attached, the allowable defocus amount is 35μ x 1.2 = 42μ,
The further away the AV value of the photographic lens used is from the open side, the larger the allowable amount of defocus becomes.

On the other hand, in an AF device using such a phase difference detection method, A
F accuracy is determined by the resolution of the AF sensor, optical system, processing algorithm, etc., but the defocus amount is 10
Currently, the accuracy is guaranteed to be around 0μ, so when using silver halide film, AF accuracy cannot be guaranteed unless the aperture value is set to 2.8 or more, and in particular, when using an image sensor such as a CCD as a photosensitive means. However, in electronic still cameras that use charging conversion to convert subject light into video signals and record them on recording media such as magnetic disks, the allowable circle of confusion varies depending on the frequency band of the video signal, but it is approximately half that, which reduces AF accuracy. It is expected that the aperture value that can be guaranteed will be a value that is far from the aperture F value of the photographic lens.

Therefore, if the photographer uses the aperture priority program to set the aperture value to the maximum F-number or a value close to the maximum maximum aperture, or if the aperture value is set to the maximum maximum F-number or a value close to the maximum maximum depending on the subject conditions, the aperture value may be set automatically to the maximum maximum F-number or a value close to the maximum maximum. Even if the exposure was correct, there were cases where the subject was out of focus.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure control system for a camera having AF and AE functions, which can achieve proper exposure in any scene, and at the same time, can take pictures without out of focus.

[Means and operations for solving the problem] The gist of the present invention to achieve the object is to provide a passive phase difference distance measuring means for detecting the subject distance, and a distance measuring means for determining the aperture value and shutter time. It is equipped with a program section and an exposure control means for setting an exposure value and shutter time based on an exposure value determined by metering the brightness of the subject, and the program section sets the aperture value to a value larger than the maximum aperture value of the photographing lens. An exposure control system for a camera is characterized in that an upper limit is set for the camera.

[Example] The present invention will be described in detail below based on an example shown in the drawings.

FIG. 1 is a block diagram showing an embodiment in which an exposure control system according to the present invention is applied to an electronic still camera.

In the figure, 1 is a photographing lens, 2 is a quick return mirror (hereinafter referred to as QRM) having a sub-mirror 2a, 3 is a shutter, 4 is an imaging device consisting of a CCD, 5 is an imaging signal processing circuit, 6 is a recording circuit, and 7 is a recording circuit. A control circuit for controlling the camera, 8 a lens information detection means for detecting distance information of the distance ring of the photographic lens 1, 9 a lens driving means for AF of the photographic lens 1, 10 a half mirror, 111 a bent-ada prism, 12 is an eyepiece, 13 is a photometric sensor, 14 is an AF sensor, 15 is a program memory in which programs such as exposure priority program mode, AF guaranteed AE mode, manual mode, etc. are stored, 16 is an aperture;
7 is a mode changeover switch for selecting each program stored in the program memory 15; when the second release switch SWI (not shown) is turned on, the half mirror
10, the photometric sensor 13 performs photometry, and the AF sensor 14 starts distance measurement.
When a second release switch (not shown) is turned on, the shutter 3 is driven and a photograph is taken using the aperture value and shutter speed in the selected program mode.

The TV-AV diagram shown in Figure 2 shows the program memory 1
Exposure priority program mode (a) stored in 5 and A
F-guaranteed AE mode ('b).

This TV-AV diagram shows the maximum aperture of the photographic lens 1 used.
In the AP guaranteed AE mode (b), the exposure value (EV) is up to a predetermined value (in this example, EV =
10) Below, the aperture value (AV) is set to a value that is several stops (F=2 in this example) smaller than the open F value, and below the above-mentioned predetermined exposure value, the shutter speed is set to this upper limit aperture value. I'm trying to turn down the TV.

In this example, the upper limit of the aperture in the AF guaranteed AE mode is set to F = 2, because if the AF accuracy is 40μ for defocus and the permissible circle of confusion is 20μ, then the AF will not work if the aperture is set to F2 or less. This is because the accuracy cannot be guaranteed and there is a possibility that an out-of-focus photograph may be taken.

Next, the operation of this embodiment will be explained based on the flowchart shown in FIG.

In step (hereinafter referred to as S) 1, if the mode selector switch 17 selects the exposure priority program mode, the exposure priority program (a) in the program memory 15 is selected.
) 5-2), determine the TV value from the set AV value 3-3), and proceed to S-4.

Distance measurement is performed in S-4, and when focusing (S-S
), the release is performed at the determined shutter speed (S-6). In this case, by setting the aperture value to an optimal value less than or equal to the maximum aperture value, the photographing area is not limited.

Also, if you select the AF guaranteed AE program mode,
AF guaranteed AE program in program memory 15 (b
), the aperture value AV and shutter speed TV are determined from the exposure value EV in step S-3. In this case, even if the aperture value is on the wide open side, the upper limit of the AV value is set several steps smaller than the aperture value, so AF accuracy can be guaranteed, and it is possible to take properly exposed photos without defocusing. can.

[Effects of the Invention] As explained above, according to the present invention, since exposure can be controlled using an aperture value that guarantees distance measurement accuracy, it is possible to obtain the effect of not losing focus and being able to take pictures with proper exposure. It will be done. −

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the camera exposure control system according to the present invention, FIG. 2 is a TV-AV diagram, and FIG. 3 is a flowchart. 1...Photographing lens 2...Quick return mirror 3...Shutter 4...Image sensor 5...
Imaging signal processing circuit 6... Recording circuit 7... Control circuit 8... Lens information detection means 9... Lens driving means 10... Half mirror
11...Penta roof prism 12...Eyepiece 13...Photometering sensor 14...AF sensor 15...Program memory 16...Aperture 17
...Mode changeover switch.

Claims (1)

[Claims] A passive distance measuring means for detecting the subject distance, a program section for determining the aperture value and shutter time, and an exposure control means for setting the exposure value and shutter time from the exposure value determined by metering the brightness of the subject. An exposure control system for a camera, characterized in that the program section sets an upper limit of the aperture value to a value larger than the maximum aperture value of the photographing lens.