JPH055088B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic exposure control device, and particularly to an automatic exposure control device used in transendoscopic photography.

In strobe photography using automatic exposure control, overexposure occurs when shooting at close range. This is because in close-up shooting, the strobe light emission is stopped near the high light output area of the strobe light emission distribution, and this time of flash emission is delayed from the appropriate flash stop time due to a delay in the flash stop signal, etc., and the high light output area is delayed by this delay. This is caused by being exposed to the same amount of light. especially,
In transendoscopic strobe photography, the effects of overexposure in short-distance strobe photography are large due to the use of long transmission paths.

Therefore, an object of the invention is to provide an automatic exposure control device that can prevent overexposure during close-range strobe photography.

An embodiment of the present invention will be described below with reference to the drawings.

According to FIG. 1, an endoscope camera 12 is attached to the eyepiece of an endoscope 11, and a connector 14 at the end of a connector 13 at the end of a universal cord 13 of the endoscope 11 is connected to a light source unit 15. .

The endoscope 11 is provided with a light guide 16a extending from the end of the endoscope to the inside of the light source unit 15, and an image guide 16b extending from the end of the endoscope to the eyepiece of the endoscope. Ru. The endoscope camera 12 is provided with a beam splitter 17 on an extension of the optical axis of the image guide 16b. A light receiving element (for example, a photodiode) 18 is provided on the side surface of the beam splitter 17 . The light receiving element 18 is connected to an integrator 20 via an amplifier 19. A switch 21 is connected in parallel to an integrating capacitor 20a of this integrator 20. The release switch 22 is connected to a signal line 23 of the endoscope 11. Similarly, the outputs of amplifier 19 and integrator 20 are connected to signal lines 24 and 25, respectively.

The output end of the amplifier 19 is connected to the input end of an A/D converter 26 of the light source unit 15 via a signal line 24. The output end of A/D converter 26 is connected to port 27 . This port 27
A CPU 28 is connected to the . CPU 28 is connected to memory 29. A set switch 30 is connected to the port 27, and a D/A converter 31 is also connected to the port 27.
and A/D converter 32 are connected. D/A
The output terminal of the converter 31 is connected to the integrator 2 of the camera 12.
It is connected to the input terminal of the comparator 33 along with the output terminal of 0. The output terminal of the comparator 33 is connected to the input terminal of the lighting control circuit 34. This illumination control circuit 34 is configured to control the emission of photographing light and collation light from a strobe tube 35 and a lamp 36.
The mirror 37 serves as the optical path of the strobe tube 35 and the lamp 3.
It is provided to switch the optical path of 6. A light receiving element (for example, a photodiode) 38 is provided to obtain an optical signal corresponding to the light incident on the light guide 16a, and this light receiving element 38 is connected to the A/D converter 32 via an amplifier 39.

The operation of the automatic exposure control device of the endoscope system will be explained with reference to the second flowchart.

First, setting data is input via the set switch 30. This setting data includes the exposure level B, information α corresponding to the short distance requiring correction, and correction ratio β. These data are film sensitivity,
It is obtained by considering the type of endoscope, type of light source unit, area to be imaged, etc. When the exposure level B is set as a set value B', there is a range of permissible error ΔB with respect to this set value B', as shown in FIG. α is a function of the short distance value D that requires correction even if this tolerance ΔB is taken into account. The correction ratio β is appropriately set according to the photographing conditions of close-range photography, which may result in overexposure. These setting values B′,
When α and β are input to the port 27 by the set switch 30, the CPU 28 outputs the setting data B', α, and β.
are respectively processed and stored in the memory 29. Once the initial values are set in this way, the operation follows the flow shown in FIG. That is, first, it is determined whether the exposure level B has been changed from the initial value. For example, if the exposure level B has been changed depending on the brightness of the desired photograph, the exposure level B is reset, and if not, it is determined whether or not the short distance determination value α has changed. When there is a change in α, α
will be reset. If there is no change, it is determined whether there is a change in the short distance correction ratio β. If there is a change in β, β is reset, and if there is no change, photometry of the emitted light is performed. In this case, lamp 3
6 is passed through the light guide 16a by the mirror 37.
A photocurrent corresponding to the incident light is output from the light receiving element 38, and this photocurrent is converted into a voltage signal by an amplifier 39, amplified, and input to the A/D converter 32. The A/D converter 32 converts the optical voltage signal into a digital signal and outputs it via the port 27.
The data is input to the CPU 28 and processed. The CP 28 stores the emitted light data in the memory 29. on the other hand,
The light from the lamp 36 passes through the light guide 16a and illuminates the subject 40. The reflected light from the subject 40 passes through the image guide 16b to the beam splitter 17.
incident on . A portion of the reflected light incident on the beam splitter 17 is incident on the light receiving element 18. The light receiving element 18 outputs a photocurrent corresponding to the incident light. The photocurrent is voltage amplified by an amplifier 19 and is supplied to an A/D converter 26 of the light source unit 15 via a signal line 24. The output of the amplifier 19 is also supplied to the integrator 20, but since the integrator 20 switch 21 is closed at this time, the integrator 20 does not perform an integrating operation.

The reflected light voltage signal input to the A/D converter 26 is input to the CPU 28 via a digitally converted port 27. The CPU 28 processes the reflected light voltage signal and stores the reflected light data in the memory 29. Thereafter, the CPU 28 calculates the ratio A between the emitted light and the reflected light using the following equation.

A=Reflected light/Emitted light This ratio A is compared with the short distance judgment value α, and A≦
When α, the CPU 28 determines that the distance is not close, and outputs the exposure level B. When A>α, CPU28
is determined to be a short distance, and outputs data of exposure level B x correction ratio β. Data B or B×β is input to the D/A converter 31 via the port 27 and input to the comparator 33 as reference data.

When the release switch 22 is closed to take a photograph in the above state, a release signal is input to the illumination control circuit 34. The illumination control circuit 34 raises the mirror 37 in response to the release signal to form an optical path for the strobe tube 35 and causes the strobe tube 35 to emit light. The strobe light illuminates the subject 40 via the light guide 16a, and the reflected light from the subject 40 enters the beam splitter 17 via the image guide 16b. The light receiving element 18 outputs a photocurrent corresponding to the strobe reflected light. At this time, since the switch 21 of the integrator 20 is closed, the light reception signal amplified by the amplifier 19 is integrated by the integrator 20. Integrator 20 outputs an integral signal as shown in FIG. 4a, and this integral signal is input to comparator 33 via signal line 25. During non-close photography, the reference data of exposure level B is input to the comparator 33 via the D/A converter 31, so when the integral signal reaches the reference value B, the output of the comparator 33 is as shown in FIG. 4b. to be reversed. When the output signal of the comparator 33 is input to the illumination control circuit 34, the strobe tube 35 stops emitting light. At this time, the light emission time of the strobe tube 35 should be t ₀ - t ₁ hour, but due to transmission delay of the integral signal, etc., the time from when the integral value reaches the reference value until the time when the strobe tube 35 stops emitting light.
There is a delay of _t1 - _t2 hours, so the actual light emission time of the strobe tube 35 is _t0 - _t2 . In other words, the delay
Overexposure occurs by t ₁ −t ₂ hours. However, in non-close-distance photography, the exposure amount for the time t ₁ - _{t 2} falls within the allowable error range, so it has almost no effect on the photograph.

When performing close-range photography, the integrator 20
An integral signal as shown in FIG. At this time, the CPU 28 determines that it is short distance mode, that is, A>α, so the comparator 33
Reference value data of B×β is input to . Therefore, the light emission of the strobe tube 35 is stopped at time _t3 when the integral signal reaches the reference value B×β. At this time, the light emission time t ₀ -t ₃ results in underexposure, but since there is a delay time t ₃ -t ₄ , the actual light emission time becomes t ₀ -t ₄ , and an appropriate exposure amount corresponding to the set value B can be obtained.

As explained above, according to the present invention, there is provided a means for automatically correcting the exposure reference value during close-range photography, where the influence of overexposure due to signal delay, etc. becomes large, so overexposure occurs during close-range photography. This can be prevented.

In the above embodiment, the comparator is provided in the light source unit, but it may also be provided in the camera. Also, the ratio of the emitted light and reflected light is A
Although only one is set, it is also possible to set a plurality of numbers and calculate β in each case to change the degree of correction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an endoscope system having an automatic exposure control device according to an embodiment of the present invention, and FIG.
The figure is a flow chart to explain the operation of the circuit in Figure 1, Figure 3 is a graph diagram showing the relationship between shooting distance and exposure amount, and Figure 4 is a time chart to explain automatic exposure control. It is a diagram. 11... Endoscope light, 12... Endoscope camera, 15
...Light source unit, 18... Light receiving element, 19...
Amplifier, 20... Integrator, 23, 24, 25...
Signal line, 26...A/D converter, 27...
...Port, 28...CPU, 29...Memory, 3
0... Set switch, 31... D/A converter, 32... A/D converter, 33... Coparator, 34... Lighting control circuit, 35... Strobe tube, 36... Lamp, 37... Mirror, 38 ……
Light receiving element, 39...amplifier.

Claims (1)

[Claims] 1. A means for photometering the emitted light from the light source, a means for photometering the reflected light from the subject, a means for calculating the ratio of the measured emitted light and the reflected light, and a means for measuring the light emitted from the subject at short distances that requires exposure compensation. A means for generating data of a short-distance correction judgment value compares the ratio of the calculation means with the short-distance correction judgment value, determines whether it is a short distance or a non-short distance, and determines a correction reference value and a non-correction reference value. an output means for outputting according to the comparison judgment result;
an automatic exposure control device comprising means for outputting an exposure stop signal when an exposure value due to the reflected light exceeds a reference value from the output means.