JPH0113370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an appropriate exposure control circuit suitable for use in a photographing device, particularly a fundus camera.

Although fundus cameras with various configurations have been proposed, the general configuration is as shown in FIG. 1. That is, light from an observation light source 1 is guided through a condenser lens 2 to a ring slit 3, and the ring slit image is transmitted through a total reflection mirror 4, a relay lens 5, a perforated mirror 6, and an objective lens 7 to the cornea of the eye 8 to be examined. An image is formed in the vicinity to illuminate the fundus, and the fundus image is observed through an objective lens 7, a perforated mirror 6, an imaging lens 9, a half mirror 10, a flip-up mirror 11, a total reflection mirror 12, and an eyepiece 13. It is composed of In addition, when photographing the fundus image with the camera 14, the flip-up mirror 11 is
At the same time, the strobe tube 15, which is a light source for photography, is emitted, and the strobe light is guided to the ring slit 3 through the condenser lens 16, and the ring slit image is observed in the above-mentioned observation. Similarly, the fundus is irradiated by connecting a wire near the cornea of the eye 8 to be examined through the total reflection mirror 4, the relay lens 5, the perforated mirror 6, and the objective lens 7, and the fundus image is transferred to the objective lens 7, perforated mirror 6, and objective lens. An image is formed on the surface of a film (not shown) mounted in the camera 14 through the image lens 9 and the half mirror 10, and the light reflected by the half mirror 10 is received by the light receiving element 18 through the condensing lens 17. The light emitting time of the strobe tube 15 is controlled to obtain an appropriate amount of exposure.

In this way, in the fundus camera, the camera 14
In general, a single camera does not have a shutter, but a flip-up mirror 11 serves as a shutter for the film attached to the camera. Therefore, the shutter speed is determined by the response speed of the flip-up mirror 11, and is generally 80 to 100 msec.

FIG. 2 is a block diagram showing the configuration of a conventional appropriate exposure control circuit used in the fundus camera shown in FIG.
1. Integration is performed by an integrator 25 comprising a capacitor 22, a discharge resistor 23, and a discharge switch 24 consisting of a field effect transistor (FET), and a comparator 2
It is supplied to one input terminal of 6. Further, photographing condition data such as film ASA sensitivity for determining the appropriate exposure amount is inputted to an arithmetic control circuit 28 such as a microcomputer via an interface 27, and these input data and RAM 29 and
A digital signal corresponding to the integral value for obtaining an appropriate exposure amount is obtained by performing necessary calculations using the ROM 30, and this digital signal is sent to the comparator 26 as an analog reference signal (V _ref ) via the digital-to-analog converter 31.
When the comparator 26 inverts its output, the waveform shaping circuit 32 outputs a strobe light emission stop signal, thereby causing the strobe tube 15 to stop emitting light. Note that a release signal for moving the flip-up mirror 11 out of the photographing optical path in order to start photographing and a strobe light emission stop signal from the waveform shaping circuit 32 are input to the arithmetic control circuit 28 via the interface 27, and these release signals and Based on the strobe light emission stop signal, a required integral control signal is supplied from the arithmetic control circuit 28 via the interface 27 to the gate of the FET constituting the discharge switch 24 of the integrator 25 to control the start and stop of integration. There is.

Next, the operation of the conventional appropriate exposure control circuit in the fundus camera mentioned above will be explained with reference to FIG.

When the release signal is supplied, the flip-up mirror 11 starts rotating so as to move out of the photographing optical path. Since this flip-up mirror 11 is generally driven by a solenoid, as shown in FIG. 3A, the flip-up mirror 11
It takes time for the mirror 1 to completely leave the photographic optical path and reach the up position, and the flip-up mirror 11 is energized for a certain period of time to maintain the flip-up mirror 11 in the up position. It takes time for the camera to reach the down position (initial position) where it completely blocks the photographing optical path.
Therefore, the response speed of the flip-up mirror 11 is
The time from when the release signal is supplied and the flip-up mirror 11 starts rotating until the flip-up mirror 11 returns to its initial position is the time _tw , and this time
As mentioned above, t _w is generally 80 to 100 msec.

A release signal is supplied, and the flip-up mirror 11
At the same time as the switch 24 starts rotating, the integral control signal rises as shown in FIG. 3B, and the discharge switch 24
is turned off and integration of the photoelectric output begins. At this point, the strobe tube 15 does not emit light yet, and the reflected light from the eye 8 illuminated by the observation light source 1 is incident on the light receiving element 18. Therefore, the output of the integrator 25 supplied to one input terminal of the comparator 26 gradually increases as shown in FIG. 3C.

The flip-up mirror 11 starts rotating, and when it reaches the completely up position, the strobe tube 1
5 emits light as shown in FIG. 3D, and the output of the integrator 25 increases rapidly accordingly.

On the other hand, the arithmetic control circuit 28
The necessary calculations are performed based on the shooting condition data such as the film ASA sensitivity input through step 7, and the D/A
An analog reference signal V _ref corresponding to an integral value for obtaining an appropriate exposure amount is supplied to the other input terminal of the comparator 26 via the converter 31 .

When the output of the comparator 26 is inverted, at that point the waveform shaping circuit 32 outputs a strobe light emission stop signal, and at the same time the strobe light emission of the strobe tube 15 is stopped, the integral control signal falls and the integration of the photoelectric output is stopped. .

In the conventional appropriate exposure control circuit described above, the full light emission time of the strobe tube 15 is generally around 5 msec, although it depends on the strobe circuit, which is extremely short compared to the response speed t _w of the flip-up mirror 11. The remaining photographing optical path opening time t _EO from when the mirror 15 stops emitting light until the flip-up mirror 11 returns to its initial position is t _EO when t _w is 100 msec.
= 50~60msec. Even if the strobe tube 15 stops emitting light during t _EO , the light emitted from the observation light source 1 is incident on the film, so the equivalent integral value of the total amount of light incident on the film during t _w is As shown in FIG. 4, there is a problem that the analog reference signal V _erf for obtaining the appropriate exposure amount calculated by calculation is higher by ΔV, resulting in overexposure by this amount. Such overexposure appears conspicuously when the observation light is bright or when the film ASA sensitivity is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide an appropriate exposure control circuit that is appropriately configured to minimize the above-mentioned overexposure and to always be able to take desired photographs with approximately the appropriate exposure amount.

The present invention is capable of irradiating a subject with light from an observation light source, while guiding the subject image to an observation optical system for observation when not photographing, and by opening the photographing optical path during photographing. It is used in a photographing device that causes a light source to emit light and irradiates the subject with the light from the observation light source to guide the subject image onto the film to take a picture, and the light from the subject is received by a light receiving element. In the appropriate exposure control circuit, the circuit controls the light emitting time of the photographing light source to obtain an appropriate amount of exposure. In order to compensate for overexposure caused by light from the observation light source entering the film at certain times, the output of the light receiving element is integrated at a predetermined period over a predetermined integration time when not photographing. a means for storing the sequential integral values while updating; and a means for storing the integral values immediately before the start of photographing stored in the storage means, the predetermined integral time, the photographing condition data, and the remaining photographing optical path opening time. The present invention is characterized by further comprising means for calculating a light emission time of the photographing light source to obtain an appropriate exposure amount based on a preset time.

The present invention will be described in detail below with reference to the drawings.

FIG. 5 is a block diagram showing the configuration of an example of the appropriate exposure control circuit of the present invention, which is applied to the fundus camera shown in FIG. 1. The photoelectric output of the light receiving element 18 is integrated by an integrator 45 comprising an amplifier 41, a capacitor 42, a discharge resistor 43, and a discharge switch 44 consisting of an FET, and is supplied to one input terminal of a first comparator 46. The signal is supplied to one input terminal of a second comparator 48 via a sample and hold circuit 47. First and second comparators 46
and the other input terminal of 48 is a D/A converter 4.
7 outputs are supplied in parallel. First comparator 46
The output is supplied to a waveform shaping circuit 50, which outputs a strobe light emission stop signal to stop the light emission of the strobe tube 15, and this signal is sent to an arithmetic control circuit such as a microcomputer via an interface 51. 52. Also,
The output of the second comparator 48 is
The signal is supplied to the arithmetic control circuit 52 via. This arithmetic control circuit 52 is also supplied with photographing condition data such as film ASA sensitivity and release signals via an interface 51, and various data input via the interface 51 and stored in the ROM 53 are supplied to the arithmetic control circuit 52. The appropriate exposure amount is calculated based on a predetermined program, and stored at a predetermined address in the RAM 54. Further, the arithmetic control circuit 52 supplies an integration control signal to control the start and stop of integration to the discharging switch 44 of the integrator 45 via the interface 51, and the sample hold circuit 47 receives the necessary sample hold control signal. In addition, the waveform shaping circuit 50 is supplied with a strobe control signal that acts as a gate signal for a strobe light emission stop signal. On the other hand, D/A converter 4
9, within the range limited by the number of input bits from the arithmetic control circuit 52 to the D/A converter 49, for example, if the number of input bits is 8 bits, sequentially add "1" from "00000000" to "11111111". The D/A converter 4
9 outputs an analog signal that increases almost linearly in accordance with the input digital signal, and at the same time, the arithmetic control circuit 52 stops adding the generated digital signals based on the output of the second comparator 48. The digital signal is stored in a predetermined address of the RAM 54. After this digital signal is stored in the RAM 54, the hold of the sample hold circuit 47 is released, and the digital signal sent to the D/A converter 49 is reset to clear its output to the lowest potential. In this way, when not photographing, the output of the light receiving element 18 is integrated at a predetermined period over a predetermined separation time, and the sample and hold circuit 4
7 in sequence. The integral value is analog-to-digital (A/D) converted and stored in a predetermined address of the RAM 54 while being updated as data for calculating a correction value. Further, the arithmetic control circuit 52 calculates a correction value by performing necessary arithmetic operations based on the integral value data written in the RAM 54 immediately before the start of shooting when the release signal is input, and stores this correction value in the RAM 54. The corrected appropriate exposure amount is obtained by subtracting it from the corrected appropriate exposure amount, and this is supplied to the other input terminal of the first and second comparators 46 and 48 through the D/A converter 49 during photographing. Configure.

Next, the operation of the proper exposure control circuit shown in FIG. 5 will be explained with reference to FIGS. 1 and 6.

Before taking a photo, open the interface 5.
The appropriate exposure amount is calculated based on the shooting condition data such as the film ASA sensitivity that is input through step 1.
The observation light is stored at a predetermined address in the RAM 54, and an integral control signal and a sample hold control signal as shown in FIG. The photoelectric output is repeatedly integrated at a predetermined period over a predetermined integration time t _p as shown in FIG.
As shown in FIG. D, samples are sequentially held and the held integral values are supplied to one input terminal of the second comparator 48. On the other hand, the D/A converter 49 is supplied with a digital signal that is successively added and increased within the range limited by the number of input bits of the D/A converter 49 as described above from the arithmetic control circuit 52.
The A converter 49 supplies the other input terminals of the first and second comparators 46 and 48 with an analog signal that increases approximately linearly as shown in FIG. 6E in response to the digital signal that increases successively. do. Then, when the arithmetic control circuit 52 detects that the output of the second comparator 48 is inverted via the interface 51, a data write pulse as shown in FIG. In addition to stopping the addition of , the digital signal at that point is used as data for calculating the correction value.
The data is stored at a predetermined address in the RAM 54. Thereafter, the hold of the sample and hold circuit 47 is released, and the digital signal to the D/A converter 49 is reset to clear its output to the lowest potential. In this way, the integral values sequentially held in the sample and hold circuit 47 are D/A converted, and these sequential digital signals are stored at a predetermined address in the RAM 54 while being updated. Therefore, when the release signal is input, the latest data written immediately before is stored. Note that, before this photograph is taken, even if the output of the first comparator 46 is inverted during D/A conversion of the integral value of the observation light, the strobe light emission stop signal is not output from the waveform shaping circuit 50. The waveform shaping circuit 50 is supplied with a strobe control signal that prevents the strobe light emission stop signal from passing through. Therefore, the waveform shaping circuit 50 does not inadvertently output a strobe light emission stop signal before taking a photograph, so that it is possible to effectively prevent the strobe circuit from malfunctioning due to this.

When a release signal is supplied due to the start of photographing, the flip-up mirror 11 moves as shown in FIG. 6G (FIG. 3A).
(same as ) leaves the photographic optical path with the characteristics shown in Here, the incident time of the observation light that affects photography is the remaining photography optical path opening time t _E0 from when the strobe tube 15 stops emitting light until the flip-up mirror 11 returns to its initial position, and this time is shown in Figure 3. As explained in , although it depends on the flashing time of the strobe tube 15, the response speed t _w of the flip-up mirror 11 is
In the case of 100 msec, t _E0 =50 to 60 msec. On the other hand, the full flash time of the strobe tube 15 is 5 m.
Since it is about sec, the remaining photographing optical path opening time t _E0
Even if the time related to t _E1 is determined for convenience to be a constant time t E1 in the range of 50 to 60 msec, the variation due to the difference in light emission time is less than 1/10, and this error is a sufficiently negligible amount. In this way, when the time related to the remaining photographing optical path opening time t _E0 is set as a constant time t _E1 , the amount of undesired observation light incident on the film, that is, the correction amount, is the observation light at a constant time t _p stored in the RAM 54. The latest data of the integral value of V ₀ (t)
Then, it is given by t _E1 /t _p ×V ₀ (t). Therefore, if the appropriate exposure amount calculated from shooting condition data such as film ASA sensitivity is V ₁ (equal to V _ref in Figure 2), then the appropriate exposure amount considering the above correction value is
V _N is given by V _N =V ₁ −t _E1 /t _p ×V ₀ (t). Therefore, in this example, at the start of shooting, the appropriate exposure amount V _N corrected by the above formula is calculated, and the corresponding digital signal is supplied from the calculation control circuit 52 to the D/A converter 49 to be converted into an analog value. the first and second comparators 46 and 4
8 and starts integrating the photographing light, and the flip-up mirror 11 is completely raised (UP).
When the state is reached, the strobe tube 15 emits light as shown in FIG. 6H. and the first comparator 46
When the output of is inverted, the waveform shaping circuit 50 outputs a strobe light emission stop signal, thereby stopping the light emission of the strobe tube 15 and stopping the integration of the photographing light. Of course, during this photographing, the waveform shaping circuit 50 is supplied with a strobe control signal that allows passage of the strobe light emission stop signal.

In this way, the exposure amount incident on the film will be the corrected appropriate exposure amount _VN until the strobe tube 15 stops emitting light, as shown by the solid line in FIG.
During the remaining photographing optical path opening time _tE0 until the flip-up mirror 11 returns to its initial position after the light emission stops, a light amount of approximately _tE1 / _tp × _V0 (t) is incident. Therefore, approximately the appropriate exposure amount V ₁ is incident during the entire period of the response speed t _w of the flip-up mirror 11 . In FIG. 7, the broken line indicates the amount of light incident on the film in the conventional proper exposure control circuit.

According to the above-described proper exposure control circuit according to the present invention, overexposure caused by observation light is corrected by measuring the intensity of observation light, so that optimal photography can always be performed. Furthermore, since the same light-receiving element 18 is used to measure the observation light and the strobe light, differences in sensitivity between the light-receiving elements are less likely to occur compared to measuring light using separate light-receiving elements. Therefore, there is an advantage that the required correction can be made with high accuracy. Additionally, one D/A
Since the converter 49 is used to perform D/A conversion of the integral value of the observation light and to send out the corrected appropriate exposure amount _VN , the circuit configuration is simplified. In addition, since the observation light is repeatedly integrated when not photographing, and the latest integrated value is used when photographing, it is possible to always perform accurate correction calculations by following the deterioration of the observation light source 1. .

Note that the present invention can be effectively applied not only to the above-mentioned fundus camera, but also to a reflection type or transmission type microphotographing apparatus using observation light, strobe light, or flash light.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an example of a fundus camera to which the proper exposure control circuit of the present invention can be applied, FIG. 2 is a block diagram showing the structure of a conventional proper exposure control circuit, and FIGS. 3A to D are A signal waveform diagram for explaining its operation, FIG. 4 is a line diagram showing the amount of light incident on the film in a fundus camera using the appropriate exposure control circuit shown in FIG. 2, and FIG. A block diagram showing the configuration of an example, FIGS. 6A to 6H are signal waveform diagrams for explaining its operation, and FIG. 7 shows a case where the appropriate exposure control circuit of the present invention is applied to the fundus camera shown in FIG. FIG. 3 is a diagram showing the amount of light incident on the film. 1... Light source for observation, 8... Eye to be examined, 9... Imaging lens, 10... Half mirror, 11... Flip-up mirror, 14... Camera, 15... Light source for photography, 18... Light receiving element, 45... Integrator, 46,
48... Comparator, 47... Sample hold circuit, 49... D/A converter, 50... Waveform shaping circuit, 51... Interface, 52... Arithmetic control circuit, 53... ROM, 54... RAM.

Claims (1)

[Scope of Claims] 1. While illuminating a subject with light from an observation light source, when not photographing, the subject image is guided to an observation optical system so that it can be observed, and when photographing, the photographing optical path is opened. It is used in a photographing device that emits light from a photographing light source, irradiates the subject together with light from the observation light source, and guides the subject image onto the film to take a photograph.The light from the subject is transmitted to a light receiving element. In the appropriate exposure control circuit, the circuit controls the light emitting time of the photographing light source to obtain an appropriate exposure amount by receiving light at In order to correct overexposure due to light from the observation light source entering the film during the shooting optical path open time, the output of the light receiving element is adjusted at a predetermined period for a predetermined integration time when not shooting. and a means of integrating
means for storing the sequential integral values while updating; and presetting in relation to the integral value immediately before the start of photographing stored in the storage means, the predetermined integration time, photographing condition data, and the remaining photographing optical path opening time. and means for calculating the light emission time of the photographing light source to obtain the proper exposure amount based on the time.