JPH0346809B2 - - Google Patents

Description

[Detailed description of the invention]

This invention involves improving a TTL photometry device,
without complicating the photodetector and photometry circuit.
The present invention relates to a photometry device that can be adapted to various photographic conditions and is particularly suitable for being incorporated into a camera. Traditionally, TTL photometry devices use an average metering method that measures the average brightness of the entire screen, a partial metering method that measures the brightness of a part of the screen, and a center-weighted average metering method that is in between. . However, the brightness distribution of the subject varies, and it is difficult to obtain a proper exposure for the main subject when the subject is backlit using average metering. Partial metering is fine for manual shooting, but when it is difficult to obtain the correct exposure, such as when the EE mechanism determines the exposure conditions immediately before the shutter release and the main subject is not in the center of the screen. There are quite a few. For this reason, a method that allows arbitrary switching between average photometry and partial photometry (Japanese Unexamined Patent Publication No. 101921/1982), and a method that divides the light receiving area of the receiver into multiple parts and appropriately combines the amount of light received for each division are available. A method (Japanese Unexamined Patent Publication No. 123030/1983) has been proposed for obtaining appropriate exposure conditions. However, in the former case, if you try to combine average metering and partial metering, you have to measure the light twice, and the metering value processing circuit becomes complicated. It becomes impossible to focus and meter at the same time. On the other hand, although the latter does not have the above-mentioned drawbacks, it is necessary to subdivide the light receiving element, and the electric circuit becomes complicated because the amount of light received by each subdivided part is measured. Further, the photographer cannot concretely or intuitively know the photometry position. This invention attempts to obtain a photometry device that eliminates the above-mentioned drawbacks by changing the transmittance of each part of the focusing plate built into the camera and measuring the brightness of each part of the field of view within the viewfinder by approximately averaging it. It is something to do. A detailed explanation will be given below with reference to the drawings. FIG. 1 is a conceptual diagram of the entire photometering device when this invention is incorporated into a single-lens reflex camera. Similar to a normal TTL single-lens reflex camera, the light to be measured enters from the photographing lens 6 and is reflected by the reflector 5. Focus the image on the rear pin 1 plate 1. The light to be measured, which has undergone partial brightness adjustment as described later with this focusing plate, is transmitted to a single point located near the exit port of the pentaprism 2, that is, the eyepiece 3.
Light amount detection is performed by the two light receiving elements 4. The focusing plate 1 is made of an electro-optical diffuser, for example a liquid crystal, and is divided into appropriate patterns, for example as shown in FIG. It is configured so that it can be applied separately. Therefore, as will be described later, by applying a pulse voltage to each section, it is possible to change the state to a transparent state, a translucent state, and a state with maximum density. For example, when photographing a person standing by the water on a beach as shown in Figure 3, the amount of light in the background is very large, and with average metering or center-weighted metering, the brightness of the background sky will affect the brightness of the central part a. The exposure of the person is slightly underexposed. In such a case, increase the voltage of the liquid crystal in parts b and c of the upper half to lower the transmittance, lower the illuminance on the focusing plate, and measure the light, or furthermore, measure the light by increasing the voltage of the liquid crystal in parts b and c of the upper half. including b, c,
By increasing the density of the liquid crystal in sections d and e and performing photometry, it is possible to prevent the person in section a from being slightly underexposed. In this way, if there is a large difference in subject brightness and the subject you want to properly expose is low brightness, the illuminance on the high brightness side is lowered by the liquid crystal and the focus plate illuminance is uniform across the entire surface. It measures light. On the other hand, if the brightness of the main subject is biased toward the high-brightness side, it goes without saying that you can lower the liquid crystal density of the objects other than the main subject and measure the entire surface on the focus board with almost uniform illuminance. FIG. 4 shows an operating circuit of a photometric device using such a focusing plate. Photoelectric element P that receives the light to be measured
The photocurrent of is logarithmically converted by the operational amplifier _O1 . On the other hand, a changeover switch _S1 is provided to compensate for differences in the output of the light-receiving elements P due to differences in the transmitting portions of the electro-optic diffuser. This switch S ₁
The level setting information and the exposure determination information from the film sensitivity setting section S and shutter speed setting section T are input to the operational amplifier _O4 together with the above light intensity information via operational amplifiers _O2 , _O3 , and _O5, respectively. ,
It is output as a voltage corresponding to the aperture value F. The AC is throttled by a solenoid, etc., as is known in the exposure control circuit.
Control the shutters. The photometric position selection switch _S2 is used to select the partial transmittance of the electro-optic diffuser plate, and is linked to the level setting switch _S1 .
The focus plate shown in and the switch selection position correspond as shown below.

[Table] Data D decodes the input from switch _S2 into outputs Sa to Se as shown in the table above. _S3 is a liquid crystal concentration changeover switch, and when turned to H, a 1 signal is output from _S0 , turning on analog switch _A1 , turning off _A2 , and setting the voltage applied to the liquid crystal to Vr. When switch S ₃ is turned to L, the output from S ₀ becomes a 0 signal, turning off analog switch A ₁ and turning on A ₂ , and the voltage applied to the liquid crystal becomes 1/2V _r . The transmittance of is improved. The OC is an oscillator that supplies reference pulses to the exposure control circuit AC, and also generates drive pulses to apply an alternating electric field to the liquid crystal. Gates G ₁ and G ₂ and analog switches Aa ₁ and Aa ₂ constitute a drive circuit for liquid crystal electrode a, and similar drive circuits are provided for electrodes b to e, respectively, but are omitted in the figure. . G ₁ and G ₂ are electrode selection gates that supply an alternating signal to the analog switch and apply an alternating voltage to electrode a only when the output of Sa of decoder D is 1. When the output from Sa is 1 and the drive pulse from the oscillator OC is 1, the analog switch Aa ₂
is turned on, and the common electrode f of the liquid crystal is switched to Af ₁
is turned on, so a voltage is applied in the direction f _(Vr) → a ₍₀₎ . Next, when the drive pulse from the oscillator OC becomes 0, the switches Aa ₁ and Af ₂ are turned on, so that a voltage is applied in the opposite direction from a _(Vr) to f ₍₀₎ . Therefore, while a signal of 1 is being output from Sa of decoder D, an AC electric field synchronized with the drive pulse from the oscillator OC is applied between electrodes a and f, and the liquid crystal between electrodes a and f is It will maintain a diffused state. The same applies to partial electrodes b to e, and predetermined portions are applied with an alternating current electric field by the output of decoder D, and are brought into a diffused state. In this embodiment, for convenience of explanation, only one portion of the liquid crystal is made transparent, but it is also possible to make a plurality of portions transparent by easily changing the configuration of the decoder. As described above, this invention uses an electro-optic diffuser for the focus plate and partially changes the light transmittance to make the illuminance almost uniform over the entire surface of the focus plate for photometry. You can always check the image of the subject as it is, and you can measure the light at the same time as focusing. Since you can operate while checking the brightness of each part in the viewfinder to ensure that the illuminance of the entire focus plate is the same, you can feel confident and you can operate in the same way no matter where the main subject is on the screen. . Conventional light receiving elements can be used, and there is no particular need to increase the number of them. A conventional photometric circuit can be used. It has many advantages such as.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a photometric device for a single-lens reflex camera incorporating the photometric device of the present invention, Fig. 2 is a diagram showing an example of classification of a focusing plate used in this invention, and Fig. 3 is a diagram showing a photometric method of a single-lens reflex camera. The explanatory diagram and Fig. 4 are explanatory diagrams of the operating circuit, and the symbols in the diagram are respectively 1: focusing plate, 2: pentaprism, 3: eyepiece, 4, P: light receiving element, 5: reflecting mirror, 6: photographing. Lens, O: operational amplifier, AC: exposure control circuit,
S: switch, D: decoder, A: analog switch, OC: reference pulse oscillator, G: gate.

Claims (1)

[Claims] 1. A photometric device in which a light-receiving element is arranged behind a focus plate, in which the entire surface of the focus plate is constituted by an electro-optic diffuser plate divided into appropriate patterns,
An electric control means is provided for independently changing the transmittance of each section of the electro-optic diffuser, and prior to photometry, the electric control means controls the electro-optic diffuser in sections other than the main subject. 1. A photometry device characterized in that the luminance of a main subject section and a section other than the main subject can be made almost equal by changing the transmittance of the photometer.