DD140297A1 - CIRCUIT ARRANGEMENT FOR EXPOSURE ADJUSTMENT - Google Patents

Description

-4-209 44 8

Title of the invention:

Circuit arrangement for exposure adjustment

Field of use:

The invention relates to a circuit arrangement for exposure adjustment of photographic cameras, in which measured the luminance of the object and the output signal is used for independent electronic exposure adjustment.

Characteristic of the known technical solutions:

Circuit arrangements for exposure adjustment are known, in which the luminance of the object is first measured at an open aperture and the aperture size associated with a preselected exposure time is calculated. When the camera shutter is pressed further, the lens shutter is "closed", reducing the illuminance reaching the photoreceiver, and when the calculated aperture value is reached, an iris stop signal is emitted.

However, the aperture stop does not take place immediately upon the occurrence of the stop signal. "The resulting aperture setting error is compensated for by using a difference signal occurring between the setpoint and actual value of the aperture setting after slight darkening of the photoreceptor to slightly correct the preselected exposure time (DE -AS 2 256 602).

The effect intended by the said working aperture measurement to correct the errors occurring in the diaphragm adjustment is unintentionally canceled out by the greater errors in the measurement of the lower illuminance on the "photoreceiver" in the region of small object luminance densities.

Object of the invention:

The invention is intended to improve the illumination accuracy in the region of low levels of object luminance

Essence of the invention:

The object of the invention is to provide a circuit arrangement for adjusting the illumination of photographic cameras, with the aid of which the illumination adjustment errors occurring at lower illuminances of the photoreceiver are eliminated and the measuring range of the camera is widened.

According to the invention, this object is achieved in that an opto-electrical level detector is used, which is designed as an actuator responsive to a given minimum object luminance for the autonomous switching off of a work aperture measurement following a blank aperture measurement. Preferably, the switching threshold of the rule detector is adjustable and the Rcgoldetektor supplied object

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* Brightness signal can be derived from the exposure metering circuit of the camera. ·

Embodiment:

The invention will be explained in more detail below with reference to an embodiment.

Show it:

Fig. 1 block diagram

Fig. 2 Flowchart

 "According to" Fig. "'" "'" T "/" is "¥ inemHiinTer" '~ effi ^'

This is connected, on the one hand, directly and, on the other hand, via a 2-level detector 4, to a circuit complex 5 which comprises a run-off control circuit determining the functional sequence of the exposure time setting and a computing and storage circuit a shutter stop magnet control circuit 7, a shutter control magnet 8, and an exposure time display means 9.

The approximate one is the following:

First, in the circuit complex 5, the sensitivity v, the Filmmaterisls used and the desired aperture size k electrically entered. By pressing a camera shutter, not shown, at the time t., A likewise not shown switch is closed and placed over this and the circuit complex 5, the entire camera circuit to battery voltage (Figure 2, a). Thus, the measurement of the object brightness is initiated at the maximum aperture of the objective aperture Ί (FIG. 2, b). The signal emitted by the photoreceiver 2

-4-

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This signal is amplified in the input amplifier 3 and supplied to the circuit complex 5 via the direct connection. In the latter, the necessary exposure time is calculated and displayed via the control circuit G in the display device 9. As the camera shutter is pressed further, the open-aperture measurement is terminated (tp) and the lens shutter closes until the closing movement is interrupted via the control circuit 6 by the shutter-stop magnet 7 in a known manner. At this time t, the shutter has up to .a ^ k deviation reaches the preset aperture value, 2e Fig. ₀

If the luminance of the object is sufficient, a further object brightness measurement is carried out in the area t / tt in the range t / tt when the working aperture is set, in order to compensate for the diaphragm adjustment error k.sub.k. FIG. the exposure time in the circuit complex 5 is corrected by a corresponding amount = with the corrected exposure time the exposure is then initiated at 6 and terminated at t ~ by the shutter secondary magnet 8, Fig. 2e.

If the object luminance is below a certain minimum value in contrast to the above-mentioned condition, the level detector responds and causes the sequence control circuit contained in the circuit complex 6 to switch off the described working aperture measurement. The exposure time formation takes place in this case only on the basis of the value calculated in the open-aperture measurement. Due to the now uncorrected aperture error, although a false exposure occurs, but this is much lower than if under these brightness ratios would still be performed Arbeitsblendeessung,.

To improve the accuracy, the switching threshold of the. Regeldetektors by the number of each preselected aperture levels is varied or the evaluation of the level takes place immediately after closing the aperture at a constant switching threshold. A camera with the device according to the invention thus ensures even at low object densities a reasonable exposure accuracy and thus an extended work area. , ,

Claims (4)

- a- 209 448 Claim: . I. Circuit arrangement for adjusting the exposure of photographic cameras, in which the measurement of the object luminance is first carried out / at open aperture and after-independent adjustment of the diaphragm to a manually preselected value at the working aperture and the output signal is fed to a computation and storage circuit for exposure time generation. characterized in that a photoelectric level detector (4) is used which is considered to be at a given minimum object level. , ^ ~ Leuc.h ± 4: Lchte ^^ Shutdown of the following on the open aperture following work aperture measurement is formed. 2. Circuit arrangement according to item 1, characterized in that the output signal of the level detector in a circuit complex (5) contained flow control circuit is supplied, which on exposure adjustment after Offenblendeessung and subsequent Arbeitsblendeessung , or can be switched to exposure setting after a full aperture metering. 3 · Circuit arrangement according to item 1, characterized in that the switching threshold of the level detector is adjustable. 4. Circuit arrangement according to item 1, characterized in that the level detector supplied object brightness signal. is derived from the Belichtungsmeßkreis (2,3) of the camera. : . For this / page drawing