GB1572654A - Photographic camera - Google Patents

Description

(54) PHOTOGRAPHIC CAMERA (71) We, EASTMAN KODAK COM PANY, a Company organized under the Laws of the State of New Jersey, United States of America of 343 State Street, Rochester. New York 14650, United States of America do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and bv the following statement: In cameras having electronic exposure control, the integral of light against time during an exposure is measured and, on reaching a predetermined value, means are operated to terminate the expoaure. The exposure control circuit normally includes a photoresponsive device and a capacitor, the voltage level to which the latter is charged being dependant upon the intensity and duration of incident illumination and being sensed to operate the exposure terminating means. The exposure terminating means is normally electromechanical in nature and, in consequence, gives rise to an inherent time lag. For daylight exposures, where the ambient lighting is substantially constant, this lag can be compensated for by initiating the timing. before the exposure commences, a time period equal to the time lag.

This can readily be seen and appreciated from Figure 1 of the accompanying drawings in which, by way of example, the timing of the exposure period commences some 5 milliseconds before the shutter opens. The capacitor charge level is indicated by curve D and reaches its predetermined charge level after time t milliseconds and operates the electromechanical means to terminate the exposure some 5 milliseconds later. The exposure duration is correct, i.e. t milliseconds because the quantity of light A measured by the photoresponsive device but not used for exposure plus the quantity of light C measured bv the photosensitive device and used for exposure is equal to the quantity of light C measured by the photosensitive device and used for exposure plus the quantity of light B used for exposure but not measured by the photoresponsive device; i.e. quantity A = quantity B under ambient lighting conditions (assumed constant).

Figure 2 assumes no ambient illumination and consequently areas of the graph there shown above the light output curve F of a flash bulb can be ignored. The quantity of light A' measured by the photoresponsive device (the charge level D' of which is shown) but not used for exposure is small in comparison with the quantity of light B' used for exposure but not measured by the photoresponsive device. This leads to over exposure by a factor where (B' + C')/(C' + A') where C' + A' is the required quantity of light for correct exposure and B' + C' is the exposure given.

In the graphs of Figures 1 and 2, the timing period t is shown as being equal or similar in both cases. This is not normally so. In the case of daylight exposure t will generally be much shorter than in the case of flash exposure. The over-exposure factor in the case of flash exposure varies in accordance with the exposure time t. Generally speaking, the shorter the exposure, the greater is the over-exposure factor. The exposure time t, assuming subjects of average reflectance, is proportional to the distance of the subject to be photographed from the light source and hence a variable attenuation of the light used for exposure, in dependance upon distance, is required.

It is an object of the present invention to provide a photographic camera, having an electronic exposure control, and capable of making exposures by ambient light or by flash light, with a simple and reliable means for attenuating the light used for exposure, in accordance with distance, when the camera is used for flash light photography.

According to the present invention there is provided a photographic still camera selectivelv operable in a daylight or a flashlight mode and having an electronic exposure control means, the output of which serves to terminate exposures in the selected mode in accordance with the quantity of light incident thereon, further including attenuating means, operable in the flash mode, for attenuating the light passing through the camera's objective lens, in accordance with the distance of a subject to be photographed. without varying the output of the exposure control means.

The invention will be described further, by way of example, with reference to Figures 3 and 4 of the accompanying drawings in which: Figure 3 is a schematic view of a shutter including electronic control means that may be used in a photographic still camera according to the present invention; and Figure 4 is a schematic view of a camera lens and a diaphragm of a camera according to the present invention which diaphragm is movable over the lens in relation to focus when exposure is made in flash light.

Figure 3 shows an exposure control apparatus of a camera according to the present invention. The apparatus includes a shutter having blades 10, 12. The blades 10, 12 are respectively biased by springs 14, 16 to open and close an exposure aperture 18.

The blade 10 is latched in its cocked position. as shown in Figure 1. by a latch 20 that is operatively connected with a release mechanism 22 of the camera. A spring 23 biases the latch 20 into its latching position.

When the release member 22 is operated, the latch 20 releases the blade 10, and the blade 10 pivots counterclockwise, as viewed in Figure 1, to open the exposure aperture 18. After the blade 10 moves to open the aperture 18, the blade 12 is held in a position to the left of the aperture 18. in which position the aperture 18 is exposed to light. An armature 24, coupled with an electromagnet 26. holds the blade 12 in this position. A spring 27 urges the armature 24 away from its latching position. An electronic circuit 28, includes a photosensor 30 such as a silicon cell, which is mounted on the camera so as to be exposed to scene brightness. The circuit 28 is energised on operation of the shutter release 22 i.e. a predetermined period of time before the shutter blade 10 opens the aperture 18. and regulates the state of the electromagnet 26 in relation to scene brightness. When the electromagnet 26 is energised, it holds the armature 24 against the force of the spring 27 and thus holds the blade 12 in the position shown in Figure 1. A timing capacitor 34. in the circuit 28, is charged at a rate depending upon the current in the photosensor 30. which in turn is related to the level of scene brightness. When the scene is very bright, the capacitor 34 charges at a rapid rate. When the scene is not so bright, the capacitor 34 charges at a correspondingly lower rate. When the charge on capacitor 34 reaches a predetermined level, the circuit 28 de-energizes the electromagnet 26, thereby allowing the armature 24 to release the blade 12 to cover the aperture an equivalent period of time later than de-energisation of the electromagnet. The exposure time (from the opening to the closing of the shutter) is thus related to the level of light striking the photosensor 30. A switch S, shunts the capacitor 34 to ground prior to the time that the shutter blade 10 is released to open the aperture 18. The opening of the switch S is arranged to take into account the timing lags of the mechanical arrangement so that the timing of the shutter is equal to the opening of the shutter. Such operation is well known in the art.

The camera (see Figure 4) also includes a lens mount 40 which is connected to the camera housing and whose light entrance is coincident with a fixed diaphragm aperture 42 (e.g. a relative aperture of f/ll).

There is provided a diaphragm means 82 for operation of the camera in ambient light.

The aperture 84 of diaphragm 82 (e.g. a relative aperture of f/16) is smaller than the fixed diaphragm aperture 42. During operation in ambient light, when the object illumination is very bright, the aperture 84 can be pivoted over the diaphragm aperture 42. For this purpose, an electromagnet (not shown) may become energised in response to an electronic exposure control means (also not shown but which includes the photosensitive element 30), to control a locking member 88 within the path of movement of the diaphragm means 82. A window 90 in the diaphragm means 82 is associated with a light entrance opening 92 for the photosensitive element 30.

In accordance with the present invention, the camera includes a further diaphragm means operative when flash illumination is to be employed. The further diaphragm means includes a ring shaped diaphragm setting means, indicated by the broken line 44 which has peripheral gear teeth and which is rotatably arranged on the lens mount 40. The peripheral gear teeth of diaphragm setting means 44 engage with the teeth of a gear wheel 46. Gear wheel 46 includes a cam 48 that controls the position of a diaphragm member 50 when the camera is focused, if a non-electronic flash, e.g.

electrically fireable or percussively fireable single or multiple-flash unit, is mounted on the camera.

The diaphragm member 50 is a doublearmed lever pivotally mounted about a pin 52 on the housing. When the diaphragm member 50 is in its inactive position, as shown bv solid lines of Figure 4, it rests against a stop 54. One arm 55 of the diaphragm member 50 is designed to form an elongated opening 56. shaped, for exam ple. like a teardrop. The teardrop opening 56 is movable into the area of the fixed aperture 42 to attenuate the light passing through the camera lens to expose the film therein. The other arm 57 has a bent-off portion 6() which, under the force of a spring 62, is urged against the cam 48.

A control lever 64, pivotally mounted about a pin 66. holds the diaphragm member 50 in its initial position which is shown by solid lines of Figure 4. A spring 68 urges the control lever 64 counterclockwise, as viewed in Figure 4, to engage an angular portion 70 of a sensing lever 72. The sensing lever 72 is mounted for movement about a pin 76 and is urged by a spring 74 into an initial position in which it abuts a projection 78 of a shutter plate.

Within the range of movement of the sensing lever 72 (as viewed in Figure 4) there is located a normally closed switch 80.

The switch 80 is connected in the circuit of a luminous diode (not shown) that indicates when scene light is below the minimum illumination for hand-held exposure and thereby provides a low-light warning signal.

The mode of operation of the apparatus will now be explained with reference to the following three conditions of the camera: 1) the camera is conditioned for operation in ambient light: 2) the camera is conditioned for operation in flash illumination with a nonelectronic flash unit; and 3) the camera is conditioned for operation in flash illumination with an electronic flash unit of the kind having an automatic light cut-off independance upon the reflected light sensed thereby.

During ambient lighting i.e. daylight operation. when no flash unit has been inserted into a socket (not shown) provided on the camera housing. the sensing lever 72 and thus the diaphragm member 50 stays in position as illustrated in Figure 4. The control lever 64 holds the diaphragm member 50 outside of the diaphragm aperture 42 (e.g. to the left side as viewed in Figure 4).

When the focus is adjusted. the diaphragm member 50 is not influenced. The diaphragm aperture is established by the diaphragm means 82 in response to the electronic exposure control means via the electromagnet and the locking member 88.

The switch 80 remains closed, thus conditioning the circuit so that the diode can indicate a possible under-exposure.

During operation in ambient lighting con editions, the time lag between the electric signal for closing the shutter (end of timing) and the actual closing of the shutter, (which in the preferred embodiment amounts to approximately 5 milliseconds) is compensated for by starting the timing 5 milliseconds before the shutter actually opens (see Figure 1) as is conventional. That is, switch Si is opened 5 milliseconds before the shutter blade 10 reaches its open position.

As may be seen by reference to Figure 1, during ambient operation, the charging of the capacitor 34, i.e. timing or integration, takes place continuously because the object illumination is constant. However, during flash illuminated operation, the time lag cannot be compensated for in the abovementioned way because the object illumination is not constant. The capacitor 34 is charged in response to the shape of the flash curve F of Figure 2, i.e. qualitatively according to the curve D' shown in Figure 2. It can be clearly seen in Figure 2 that over the same period of time of about 5 milliseconds the amount of light emitted by the flash at the beginning of the flash curve (Area A') is totally different from that (Area B') at the end of the flash curve so that compensation of the time lag cannot be achieved by providing for an earlier start of the timing operation.

According to the present invention, when a flash unit is used, the timing is started prior to the shutter opening as in operation under ambient lighting conditions, and the time lag that occurs at the end of the timing operation is compensated for by the second diaphragm member 55 which is placed over the diaphragm aperture 42. The size of the aperture of the second diaphragm member is related to both the time lag and the distance of the subject from the camera.

Since the intensity of subject illumination by the flash light, and camera focus, both depend on the photographic subject distance, the size of the aperture of the second diaphragm is varied as a function of camera focus.

When an electrically ignitable, single or multiple flash unit is mounted on the camera, the flash unit (not shown) pivots the sensing lever 72 from its initial position (shown in Figure 4) into the position labelled "A" in Figure 4. During this operation, the sensing lever 72 rotates the control lever 64 via its angular portion 70 (see phantom lines of Figure 4), freeing the diaphragm member 50 so that the bent-off portion 60 follows the cam 48 over the total stroke of the cam. In response to focus, i.e. rotation of the gear wheel 46, the opening 56 is pivoted into the area of. the diaphragm aperture 42, to a degree depending upon the focus setting, thereby varying the size of that aperture. Because the size of the opening 56 is related to the time lag and focus, the exposure error resulting from the time lag is compensated for in the case of operation during flash illumination.

When the sensing lever 72 is depressed, the under-exposure switch 80 is opened at the same time so that the low light warning signal provided by luminous diode is disabled during flash operation.

As above stated. in response to ambient illumination, the diaphragm means 82 for daylight is in the position shown in Figure 4 (dark object) or in the position in which it covers the diaphragm aperture 42 (bright object), not shown. When using fill-in light on a subject in the case of bright outdoor lighting, e.g. when the subject is backlighted. the diaphragm aperture 84 of the diaphragm means 82 is still effective.

In the third mode of operation, i.e. during illumination of a subject by an automatic electronic flash unit, the sensing lever 72 is arranged to be pivoted by an appropriate base of the flash unit. however. to a smaller degree until it reaches the position "B" shown in Figure 4. This movement causes the sensing lever 72 to open the switch 80 to disable the luminous diode. However, the diaphragm member 50 is not released; and therefore the bent-off portion 60 cannot follow the cam 48 when focus is adjusted.

This means that the working aperture. in the case of the flash operation with an electronic flash unit. is fill (diaphragm aperture 42) or f/16 (diaphragm aperture 84) depending on the ambient illumination. The amount of light supplied by the electronic flash unit is metered by the flash unit itself.

In order to achieve optimum exposure of the film, further factors depending upon time and light conditions, respectively. can also be taken into account when shaping the opening 56 such as, for instance, the Schwarzschild-effect. i.e. the change of the ASA (D.I.N.) speed in the case of different exposure times of the film.

WHAT WE CLAIM IS: 1. A photographic still camera selectively operable in a daylight or a flashlight mode and having an electronic exposure control means, the output of which serves to terminate exposures in the selected mode in accordance with the quantity of light incident thereon, further including attenuating means, operable in the flash mode, for attenuating the light passing through the camera's objective lens. in accordance with the distance of a subject to be photographed. without varying the output of the exposure control means.

2. A camera as claimed in Claim 1 wherein the attenuating means comprises a diaphragm member, the camera including focusing means for operating the diaphragm member.

3. A camera as claimed in Claim 2 wherein the focusing means includes a cam and the diaphragm member includes a cam follower for engaging the cam.

4. A camera as claimed in Claim 2 or 3 wherein the diaphragm member has a teardrop shaped aperture of shape functionally determined in accordance with the desired attenuation.

5. A camera as claimed in any of Claims 1 to 4 further including stop means inoperative in the flash light mode, for preventing operation of the attenuating means.

6. A camera as claimed in any preceding Claim including a low-light warning signal and means for disabling the signal when the camera is in the flash light mode.

7. A camera as claimed in any preceding Claim including further diaphragm means controllable electronically in accordance with sensed illumination.

8. A camera as claimed in any preceding Claim adapted to receive an automatic electronic flash unit including disabling means for disabling the attenuating means when such a flash unit is received by the camera.

9. A photographic still camera substantially as hereinbefore described with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. time lag is compensated for in the case of operation during flash illumination. When the sensing lever 72 is depressed, the under-exposure switch 80 is opened at the same time so that the low light warning signal provided by luminous diode is disabled during flash operation. As above stated. in response to ambient illumination, the diaphragm means 82 for daylight is in the position shown in Figure 4 (dark object) or in the position in which it covers the diaphragm aperture 42 (bright object), not shown. When using fill-in light on a subject in the case of bright outdoor lighting, e.g. when the subject is backlighted. the diaphragm aperture 84 of the diaphragm means 82 is still effective. In the third mode of operation, i.e. during illumination of a subject by an automatic electronic flash unit, the sensing lever 72 is arranged to be pivoted by an appropriate base of the flash unit. however. to a smaller degree until it reaches the position "B" shown in Figure 4. This movement causes the sensing lever 72 to open the switch 80 to disable the luminous diode. However, the diaphragm member 50 is not released; and therefore the bent-off portion 60 cannot follow the cam 48 when focus is adjusted. This means that the working aperture. in the case of the flash operation with an electronic flash unit. is fill (diaphragm aperture 42) or f/16 (diaphragm aperture 84) depending on the ambient illumination. The amount of light supplied by the electronic flash unit is metered by the flash unit itself. In order to achieve optimum exposure of the film, further factors depending upon time and light conditions, respectively. can also be taken into account when shaping the opening 56 such as, for instance, the Schwarzschild-effect. i.e. the change of the ASA (D.I.N.) speed in the case of different exposure times of the film. WHAT WE CLAIM IS:

1. A photographic still camera selectively operable in a daylight or a flashlight mode and having an electronic exposure control means, the output of which serves to terminate exposures in the selected mode in accordance with the quantity of light incident thereon, further including attenuating means, operable in the flash mode, for attenuating the light passing through the camera's objective lens. in accordance with the distance of a subject to be photographed. without varying the output of the exposure control means.

2. A camera as claimed in Claim 1 wherein the attenuating means comprises a diaphragm member, the camera including focusing means for operating the diaphragm member.

3. A camera as claimed in Claim 2 wherein the focusing means includes a cam and the diaphragm member includes a cam follower for engaging the cam.

4. A camera as claimed in Claim 2 or 3 wherein the diaphragm member has a teardrop shaped aperture of shape functionally determined in accordance with the desired attenuation.

5. A camera as claimed in any of Claims 1 to 4 further including stop means inoperative in the flash light mode, for preventing operation of the attenuating means.

6. A camera as claimed in any preceding Claim including a low-light warning signal and means for disabling the signal when the camera is in the flash light mode.

7. A camera as claimed in any preceding Claim including further diaphragm means controllable electronically in accordance with sensed illumination.

8. A camera as claimed in any preceding Claim adapted to receive an automatic electronic flash unit including disabling means for disabling the attenuating means when such a flash unit is received by the camera.

9. A photographic still camera substantially as hereinbefore described with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.