JPS5830733A - Direct photometric method capable of correcting difference of film reflectance - Google Patents

Abstract

PURPOSE:To measure accurately the brightness of an object to obtain a proper exposure, by considering the exposure correction quantity to control an exposure element at a photographing time. CONSTITUTION:Before photographing, the light of a light emitting element 1 is reflected by a shutter front curtain and a used film 4, and each output of a photodetector 3 is supplied to an operating circuit 13, and an exposure correction quantity is operated on the basis of the ratio or difference to a reference reflectance, and the operated value is stored in a storage circuit 19. In photographing, the light from an object is reflected by the film 4 and is made incident to the photodetector 3, and the output is supplied to an operating circuit 15 through a direct photometric circuit 20. In the circuit 15, a proper exposure time is calculated on a basis of respective outputs of the storage circuit 19, the photometric circuit 20, an ASA information input circuit 21, and an operating circuit 25 for display, and a shutter controlling signal is given to a magnet controlling circuit 22 to control the exposure time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct photometry method capable of correcting differences in reflectance of various films in an aperture-priority direct photometry AE camera.

The so-called direct metering method, in which the exposure time is calculated by measuring the light reflected from the film after the shutter is opened, is an excellent method that can respond to changes in subject brightness during exposure and does not require complicated memory circuits. Because of its unique characteristics, it is becoming the mainstream photometry method for cameras in the future.

Regardless of the type of versatility or difference between each film manufacturer, it is assumed that the brightness falls within a narrow range of about 20 to 30%, and the average value is set as the reference reflectance and the brightness of the subject is measured. ing. In addition, in a camera with a 7-ocal plane shutter, the front surface of the front shutter curtain is designed to have almost the same reflectance as the above-mentioned standard reflectance so that it can be used without any problem even during high-speed exposure.

However, according to the results of actually measuring the reflectance of various commercially available films, the difference in reflectance is surprisingly large, and in extreme cases, it is not uncommon for the photoelectric conversion value to have a difference exceeding ±IEvt-. Furthermore, it is completely unpredictable what kind of reflectivity films will appear in the future.

In this way, when photographing using films with different reflectances, it is impossible to detect the entire brightness of the subject by simply measuring the reflected light from the film.

In other words, even if the intensity of the reflected light is the same, if the film has a high reflectance, the subject brightness will be low and the image will be underexposed.
In the case of a film with low reflectance, the subject brightness is high and overexposure occurs.

In particular, color reversal film, high-resolution film,
When using a film with extremely narrow latitude, such as a high contrast film or an instant film, the difference in reflectance of the film is very likely to have fatal consequences.

This invention was made in view of the above points, and is capable of correcting differences in film reflectance so that proper exposure can always be obtained regardless of the reflectance of the film used in an aperture-priority direct metering AE camera. The purpose is to provide a direct photometry method.

Therefore, according to the first invention, prior to photographing, the reflectance of the film used is measured and the difference from a predetermined reference reflectance is stored as an exposure compensation amount, and the exposure compensation amount is calculated by shutter control at the time of photography. In addition to the storage of the exposure correction amount in the first invention, the circuit further provides a second invention that, in addition to storing the exposure correction amount in the first invention, the exposure correction amount is determined at the time of shooting according to the display shutter speed calculated by the display calculation circuit in the viewfinder. By correcting this, it is possible to obtain accurate exposure even when the shutter speed is high in an AE camera with an aperture-priority focal plane shutter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention applied to an eye reflex camera with a focal plane shutter will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of a camera implementing the direct photometry method according to the present invention, and FIG. 2 is a time chart showing the timing of opening and closing of each switch circuit during reflectance measurement.

In FIG. 1, a light emitting element 1 such as a light emitting diode is provided in the mirror box of an eye reflex camera, for example on the back of a mirror 2, so that the light emitting element 1 is retracted out of the photographing optical path during photographing, and the mirror box A light-receiving element 3 is fixed outside the lower photographing optical path so that it can receive the light reflected from the light-emitting element 1 by the film 4, and when photographing, the light from the subject that passes through the photographic lens 5 and is reflected by the film 4. Make it possible to receive light rays.

Furthermore, a light receiving element 8 for preliminary photometry is provided in the finder optical path, for example, behind the pentaprism 6 and above the eyepiece lens 7, so that it can receive the light beam from the focus plate 9, and the finder screen of the focus plate 9 is provided. A large number of light emitting elements 10 such as light emitting diodes are provided outside to display shutter speed, aperture value, etc. in the finder.

The light incident on the light receiving element 6 is converted into an electrical signal by a MOS operational amplifier 11 and input to an exposure correction amount calculation circuit 16 through a switch circuit 12.

The exposure correction amount calculation circuit 16 receives an input from the MOS operational amplifier 11 when the light receiving element 6 receives reflected light from the front curtain of the focal-brain shutter having a preset reference reflectance, and an input from the MOS operational amplifier 11 when the light receiving element 3 receives reflected light from the film used. The exposure correction amount is calculated based on the ratio or difference with the input from the MOS operational amplifier 11 when the reflected light is received, and is stored in the exposure correction amount storage circuit 19 via the switch circuit 18.

During photographing, the direct photometry circuit 20 inputs and integrates the output of the MOS operational amplifier 11, and inputs the photometry output to the arithmetic circuit 15 for controlling all shutters.

The shack control arithmetic circuit 15 is a direct ijl! 1
In addition to the photometric value from the optical circuit 20, the exposure correction amount from the exposure correction amount memory circuit 19, the film sensitivity information 1 from the ASA information manual input 1, and the display of the calculation 1 circuit 25 for displaying the power. inputs the shutter speed for the camera, calculates the entire appropriate exposure time, inputs the shutter control signal ST'c to the magnet control circuit 22, and releases the shutter 27'! zm control to control the exposure time. In addition, when using the strobe, the charge completion signal RD' is pulled from the strobe circuit 28, an appropriate light emission amount is calculated, and a strobe light emission control signal SQ is output to the strobe circuit to control the light emission amount (light emission time) of the strobe.

On the other hand, a light receiving element 8 for preliminary photometry and a MOS operational amplifier.

The photometric output from 26 is input to the display arithmetic circuit 25 along with film sensitivity information and aperture information from the ASA information input circuit 21 and the aperture information input circuit 24.

The display arithmetic circuit 25 calculates the shutter speed, etc. based on this input information before photographing, and causes the display circuit 26 to emit light from the light emitting element 10 for display in the viewfinder to display the ζ shutter speed, aperture value, overexposure, and underexposure. etc. will be displayed.

At the same time, the display shutter speed calculated by the display calculation circuit 25 is also input to the shutter control calculation circuit 15, and the exposure compensation amount input from the exposure compensation amount storage circuit 19 is determined according to the display shutter speed. Fix it.

The photographed number counting circuit 14 counts the number of photographed images and also controls the timing of operation of the timing circuit 169, the light emitting circuit 17.degree., and the arithmetic circuit 15 for controlling the 7-pointer.

Next, with reference to FIG. 2, the operational sequence of this implementation will be explained.

When the release button (not shown) is pressed during the 9 blank periods from loading the film to starting shooting, the power switch is turned on and the power supply voltage Vcc is applied to each circuit, causing the mirror 2 to rise, and when the mirror is completely raised. A mirror amplifier completion signal is issued, and the light emitting element 1 for reflectance measurement emits light in response to a command from the photographic number counting circuit 14. After that, the switch circuit 12 receives all the signals from the timing circuit 16 and instantaneously closes, causing the light emitting element 1 to emit light. Extinguish.

As a result, the light from the light emitting element 1 is reflected by the front curtain of the shutter, which has a reference reflectance that is approximately the same as the average reflectance of the film, and enters the light receiving element 3, and its output is exposed through the MOS operational amplifier 11 and the switch circuit 12. Correction amount calculation circuit 1
6 and is temporarily stored as the reference reflectance.

Next, in response to a command from the shot number counting circuit 14, the output of the shutter control calculation circuit 15 becomes the shutter fully open second, such as 1/125 second, and the shutter front curtain starts running, and when the shutter is fully opened, the light emitting element is activated. 1 emits light again, and during the light emission, the switch circuit 12 is instantaneously closed and the light emitting element 1 extinguishes the light.

At this time, the light from the light emitting element 1 is reflected by the film 4 used and enters the light receiving element 69, and its output is M
OS operational amplifier 11. The entire diameter of the switch circuit 12 is manually inputted to the exposure compensation amount calculation circuit 16, and the exposure compensation amount is calculated based on the ratio or difference with the reference reflectance of the shutter front curtain that has been temporarily stored in advance, and the value is sent from the timing circuit 16. Exposure compensation amount storage circuit 19 via a switch circuit 18 that closes with a signal of
will be stored until the next time you open the camera back to remove the film.

When the blank shot is finished and the normal shooting state is reached, the signal from the shot number counting circuit 14 stops the signal that activates the timing circuit 169 and the light emitting circuit 17 and the signal that controls the shutter speed to full-open speed, and then releases the shutter. When the similar mirror 2 is raised by pressing the button, the light ray from the subject passes through the photographic lens 5 and is reflected by the shutter front curtain and the film 4, and enters the light receiving element 6, the output of which is converted into an electrical signal by the MOS operational amplifier 11. , are input to the direct photometry circuit 2o, and the output thereof is input to the shank control arithmetic circuit 15.

In the shutter control calculation circuit 15, the exposure correction amount storage circuit 19. Direct photometry circuit 20. ASA information information input circuit 2 9 Accordingly, an appropriate exposure time is calculated, and a shutter control signal ST is output to the magnet control circuit 22 to control the exposure time. Furthermore, when using a strobe, a strobe light emission amount control signal SQ is output to the strobe circuit 28.

The reason why the output of the display arithmetic circuit 25 is input to the shutter control arithmetic circuit 15 will be explained below.

In a camera with a focal plane shutter, after the release button is pressed, the light from the subject that is received by the light receiving element 3 becomes both reflected light from the shutter front curtain and reflected light from the film surface, but if the shutter speed is slow When the speed is high, the ratio of light reflected from the film surface is large, and when the speed is high, the ratio of light reflected from the front shutter curtain becomes large. That is, if the shutter speed is extremely slow, it is necessary to introduce a correction amount based on film reflectance of nearly 100%, but if the shutter speed is fast, the correction amount may be small.

Therefore, the full screen running time of the first curtain [ms] Ts:
Assuming that R is the correction factor, as is clear from FIG. 6, (a) when the photometric range of the light receiving element 6 is the central spot (1) Ts
< When Tr/2, R=0Ts (b) When the photometry range of the light receiving element 6 is averaged over the entire surface, it is expressed as Tr Ts.

Here, assuming that the full-screen running time Tr of the shutter front curtain is 8 ms, the correction factors corresponding to each shutter shutter time (shutter speed) are as shown in the following table.

In reality, the photometry range of the light-receiving element 6 is usually center-weighted photometry, so the correction factor is (a) in the table above.

A desirable value is approximately the intermediate value in (b).

Extremely accurate exposure can be achieved by correcting the exposure compensation amount by multiplying the exposure compensation amount input from the exposure compensation amount storage circuit 19 to the shutter control arithmetic circuit 15 by a correction factor corresponding to the shutter speed. Time is calculated.

In addition, in the above embodiment, in order to avoid the influence of the light quantity error of the light emitting element 1 and the influence of the edge deviation error of the light receiving element 3, the reflectance of the front curtain of the shutter is used as the reference reflectance, and the ratio with the reflectance of the film used is calculated. Alternatively, the amount of exposure compensation was calculated based on the difference, but if the light intensity and output of the two elements mentioned above can be kept constant, the amount of reflection on the film surface can be measured with a cap on the photographic lens, and the standard set separately and memorized in advance can be used. The exposure correction amount may be calculated based on the ratio or difference with the reflectance.

Furthermore, as in Jin's example, when determining the exposure compensation amount as a ratio to the reference reflectance of the shutter front curtain, the light emitting element 1 is not necessarily necessary, and measurement can be performed using external light that has passed through the photographic lens. If direct photometry is performed only during strobe photography when the focal plane shutter is fully open, or if it is applied to a lens shutter camera, there is no need to modify the exposure compensation amount based on the display shutter speed.

Furthermore, in the above embodiment, the case where this invention is applied to a 35-lens reflex camera has been described, but in the case of a camera other than a 35-frame camera that does not require aerial photography, blank spaces at the left, right, top, and bottom of the screen may be used. It is also possible to measure the reflectance of a film by using a 3D camera, and it can be applied to cameras other than eye reflex cameras without any problems.

Furthermore, when using a perforated film such as 35m film or 70m film, a light emitting element is provided opposite the 3rd part of the perforane, and a light receiving element that receives the light reflected by the film surface of this light emitting element is used for photometry during shooting. In addition, the surface of the perforane 3 passing portion of the film pressure bonding plate is provided separately from the light receiving element for use as a total reference reflection surface, and prior to shooting,
By alternately measuring the reflectance of the film pressure bonding plate and the film while the film is being transported, it is possible to calculate the exposure correction amount without using the aerial photographing section.

As described above, according to the first invention, prior to photographing, the reflectance of the film used is measured, the exposure correction amount is calculated and stored based on the ratio or difference with the reference reflectance, and the exposure compensation amount is calculated and stored at the time of photographing. Since the exposure factors such as exposure time and strobe light emission amount are controlled by taking into account the amount of correction, no matter what reflectance film is used or what kind of film appears in the future, the brightness of the subject can be accurately controlled. You can measure and give the proper exposure.

Furthermore, in the second invention, the correction amount is corrected according to the display shutter speed calculated by the display calculation circuit in the viewfinder, so that when the direct photometry AE camera is equipped with a focal plane shutter, the shutter speed is reduced in seconds. It has the excellent effect of allowing extremely accurate exposure regardless of the time.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a camera that implements the direct photometry method according to the present invention, Fig. 2 is a time chart showing the operation time of each part when measuring the film reflectance, and Fig. 6 is a time chart showing the operation time of each part when measuring the film reflectance. FIG. 2 is a diagram showing the relationship between shutter operation and photometry timing. 1... Light emitting element for film reflectance measurement 6... Light receiving element 4... Film 5... Photographing lens
8... Light receiving element for preliminary photometry 16... Exposure compensation amount calculation circuit 14... Shot number counting circuit 15... Shutter control calculation circuit 19... Exposure compensation amount storage circuit 20... Direct photometry Circuit 25...display arithmetic circuit

Claims (1)

[Claims] 1. In an aperture-priority direct metering AE camera, prior to shooting, the reflectance of the film used is measured, and the amount of exposure compensation is calculated based on the ratio or difference with a predetermined reference reflectance.
This method corrects differences in film reflectance by storing the exposure compensation amount in memory and inputting the exposure compensation amount into a shutter control calculation circuit at the time of shooting to control all exposure elements such as exposure time and strobe light emission amount. A possible direct photometry method. 2. A direct photometry method capable of correcting differences in film reflectance according to claim 1, wherein the reflectance of the film used is measured during the aerial photography period from loading the film to starting shooting. 6. A die capable of correcting the difference in film reflectance according to claim 1 or 2, which measures the reflectance of the film used using a light emitting element and a light receiving element provided outside the photographing optical path in the camera body. photometry method. 4. A direct photometry method capable of correcting differences in film reflectance according to any one of claims 1 to 3, wherein the exposure correction amount is stored until the camera back cover is next opened. 5. In a direct metering AE camera with an aperture-priority focal plane shutter, the amount of exposure compensation is memorized prior to shooting, and at the time of shooting, the amount of exposure compensation is input to the arithmetic circuit for shutter control, and the amount of exposure compensation calculated by the arithmetic circuit for display in the viewfinder is stored. The difference in film reflectance is characterized by inputting a shutter speed and correcting the exposure correction amount according to the display shutter speed to control exposure elements such as exposure time and strobe light emission amount. Direct photometry method that can be corrected. 6. A direct photometry method capable of correcting a difference in film reflectance according to claim 5, wherein the reference reflectance is the reflectance of a 7,1'-one force plane shutter front curtain.