JP3137966B2 - Method and apparatus for correcting leakage current of photometric element in TTL division photometry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention, in a TTL split photometry device, prevents a leak current from entering a photometry element from another photometry element into one photometry element of a divided subject screen and causing erroneous photometry. And a method and apparatus for obtaining correct photometric values.

(Problems of the Related Art and the Invention) In the case of using TTL split photometry, where the SPD is used as a photometric element, considering split photometry on the subject screen as shown in FIGS. 2 and 3, leakage current from each part of the multi-split SPD is considered. And correct photometric values cannot be obtained. As a correction method, there is a method of reducing the influence of the leak current by widening the isolation between the SPDs, but this method increases the dead zone. Also, JP-A-59-46
As described in Japanese Patent Publication No. 521, there is a method in which an unnecessary SPD anode and cathode are short-circuited at the time of photometry so as not to generate a leak current. However, an extra switch circuit is required for that purpose. There is also a method of preventing leakage current by installing an amplifier in each SPD, but the number of amplifiers is required by the number of SPDs, and the circuit becomes complicated.

(Means for Solving the Problems) In view of the above-described circumstances, the present invention provides a partial photometry unit that performs photometry of one area of a multi-divided subject screen subjected to TTL division photometry, Other photometric means for performing photometry in other areas except for one area, and arithmetic storage means for calculating the photometric output of these photometric means and storing the data, and providing a uniform luminous flux from the photometric surface to both photometric means. The output (EVa) of the partial photometric unit when the light beam is received from the photometric surface in a state of irradiating and short-circuiting between the anode and the cathode of the other unit photometric device and blocking the leak current; The output (EVA) of the partial photometric means when the light flux from the photometric surface is received in a state where the leak current is permitted by opening between the anode and the cathode of the means and the state in which the leak current of the partial photometric means is permitted When receiving the luminous flux from the photometric surface at The output (EVB) of the other-part photometric means of
= EVA-K · 2 ^{(EVB-EVA) The} correction coefficient K is obtained in advance and the term related to the correction coefficient K is subtracted from the photometry output, so that the photometric output is not affected by the leak current from the other photometric means. The present invention provides a method for correcting a leak current of a photometric element in TTL division photometry, characterized by obtaining

Further, a partial photometric unit that performs photometry in one area of the multi-divided subject screen that is subjected to TTL division photometry, and another unit photometric unit that performs photometry in another area excluding the one area of the screen, An output (EVa) of the partial photometric means when the two photometric means are irradiated with a uniform light beam from the photometric surface and the light beam from the photometric surface is received in a state where the leak current of the other photometric means is blocked. And an output (EVA) of the partial photometric unit when the light flux from the photometric surface is received in a state where the leak current of the other photometric unit is allowed and a leak current of the partial photometric unit is allowed. The output (EVB) of the other part photometric means when receiving the light beam from the photometric surface is measured in advance, and the correction coefficient K calculated and calculated by the equation EVa = EVA-K · 2 ^(EVB-EVA) is stored in advance. In addition, the output of the two photometric means and the correction coefficient K By providing the leakage current compensation device of the photometric element in TTL split photometry is characterized in that an arithmetic memory means for calculating a photometric output which is not affected by the leakage current of the other portion photometric means.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the apparatus of the present invention, FIG. 2 is a diagram showing an example of division of a subject screen, and FIG. 3 is a diagram showing an example of division of another subject screen.

In FIG. 1, SPDs 1, 2, 3, 4, and 5 respectively correspond to A, B, C, D, and E in FIG.
The photocurrent generated from D is logarithmically compressed by a logarithmic compressor 6, A / D-converted by an A / D converter 7, and a computing unit 8 of a photometric optical system that uses a leak current of each partial parameter as a parameter. The operation of calculating the correction formula and obtaining the true photometric value is performed. 9 to 13 are switches, and 14 is a regulator.

Next, the correction formula will be described. For simplicity of explanation, the two-split system in FIG. 2 will be described. The central part A and the peripheral part, where EVa is the true EV value (exposure value) that is not affected by the leakage current of the other part of the photometry element, EVA is the EV value that includes the influence of the leakage current of the other part of the photometry element, and K is the correction coefficient. When light is measured by receiving a light beam from a light measuring surface having a uniform luminance with B, the true EV value of the central portion A can be obtained by the following equation: EVa = EVA-K (1)

Therefore, toward the surface light source having uniform brightness, the light flux of the photometric surface is irradiated to both the central portion A and the peripheral portion B, and the SP of the portion B is irradiated.
The EV value EVA of the central part A when the anode and the cathode of D are opened is measured, and then the central part A and the peripheral part B are irradiated with the same luminous flux. By metering the EV value EVa of the central portion A when the cathode is short-circuited, the correction coefficient K can be obtained by the following equation: K = EVA−EVa (2)

If the correction coefficient K is stored in the arithmetic unit 8, when the central portion A and the peripheral portion B have the same luminance, a true EVa value of the central portion A which is not affected by the leakage current of the peripheral portion B can be obtained. .

However, the brightness of the central portion A and the peripheral portion B may naturally be different. For example, if the brightness doubles, the correction coefficient K
Also needs to be doubled.

Therefore, if the EV value of the peripheral portion B including the influence of the leak current in the central portion A is EVB, the true value can be obtained by the following equation: EVa = EVA−K · 2 ^(EVB−EVA) EVa value can be obtained.

As described above, the correction coefficient K is determined by taking the difference between the EV value affected by the leak current and the EV value not affected by the leak current as an influence component. The present invention can be applied to the case of multi-division as shown in FIG. In this case, the correction equation is as follows.

EVa = EVA−Kb · 2 ^(EVB-EVA) −Kc · 2 ^(EVC-EVA) −Kd · 2 ^(EVD-EVA) −Ke · 2 ^(EVE-EVA)・ ・ (4) C, D, and E
The EV values are EVC, EVD, and EVE, respectively, and the correction coefficients are Kb, Kc, and Kb.
Here, d and Ke are set, and Kb is obtained by Expression (3), and other coefficients are obtained in advance by applying Expression (3), respectively. Note that this correction may cause some errors,
By using the corrected value for the exponent of 2 in Equation 3 or Equation 4 and performing correction twice or many times, accurate correction can be achieved.

(Effects) As described in detail above, according to the present invention, accurate TTL division photometry can be performed with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the apparatus of the present invention, FIG. 2 is a diagram showing an example of division of a subject screen, and FIG. 3 is a diagram showing an example of division of another subject screen. 1 to 5 SPD, 6 logarithmic compressor, 7 AD converter, 8 arithmetic unit, 9 to 13 switches, 14 regulator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01J 1/44 G03B 7/28

Claims (2)

(57) [Claims] 1. A partial photometer for taking light metering of one area of a multi-divided subject screen subjected to TTL split photometry, and another part metering taking charge of photometry of another area excluding said one area of the screen. Means, and a calculation storage means for calculating the photometric output of these photometric means and storing the data, irradiating a uniform light flux from the photometric surface to both photometric means, and between the anode and the cathode of the other part photometric means. An output (EVa) of the partial photometric unit when receiving the luminous flux from the photometric surface in a state where the leak current is short-circuited and an opening between the anode and the cathode of the other photometric unit allow a leak current. The output (EVA) of the partial photometric means when receiving the light flux from the photometric surface in a state where the light flux is received from the photometric surface in a state where the leak current of the partial photometric means is allowed. Set the output (EVB) of the photometry Measure, EVa = EVA-
K · 2 ^(EVB-EVA) to obtain the correction coefficient K in advance and obtain a photometric output that is not affected by leakage current from other photometric means by subtracting the term related to the correction coefficient K from the photometric output. A leak current correction method for a photometric element in TTL split photometry, characterized by the following. 2. A partial light metering means for performing light metering of one area of a multi-divided subject screen subjected to TTL split metering, and another light metering section for performing light metering of another area other than the one area of the screen. Means for irradiating the light measuring means with a uniform light flux from the light measuring surface and outputting the partial light measuring means when receiving the light flux from the light measuring surface in a state in which the leak current of the other light measuring means is cut off. (EVa), the output (EVA) of the partial photometric unit and the leak current of the partial photometric unit when the light flux from the photometric surface is received in a state where the leak current of the other photometric unit is permitted. In this state, the output (EVB) of the other photometric means when receiving the light beam from the photometric surface is measured in advance, and the correction coefficient K calculated and calculated by the equation EVa = EVA−K · 2 ^(EVB−EVA) Is stored in advance, and the outputs of the two photometric means and the correction A device for correcting a leak current of a photometric element in TTL split photometry, comprising: a calculation storage means for calculating a photometric output that is not affected by a leak current of another portion photometric means using a coefficient K.