JPS62245229A - Measuring device for transmittance of focal plate in camera - Google Patents

Abstract

PURPOSE:To automatize correction of exposure by comparing and operating respective photometric values of the first photometric system, where the transmitted light of a photographic lens is transmitted through a focusing screen and is measured, and the second photometric system, where the transmitted light of the photographic lens is reflected on a shutter curtain without being transmitted through the focal plate and is measured, to calculate the transmittance of the focusing screen. CONSTITUTION:The transmitted light of a photographic lens 1a is measured by the first photometric system 2 before the first blind exposure. At this time, the transmitted light of the photographic lens 1a is reflected on a quick return mirror 2a and is amplified by an amplifier 5 and is inputted to a logarithmic compressor 6. When the first blind exposure is performed and the quick return mirror 2a is displaced to a rise position, the transmitted light of the photographic lens 1a is reflected on a shutter curtain 3b and is led to a TTL light receiving part 3a and is measured by the second photometric system 3. The difference between an object luminance voltage Bv1 just before the first blind exposure and that Bv2 just after the first blind exposure is calculated, and the calculated variation is compared with a certain quantity (a maximum light quantity variance allowable voltage DELTABvmax); and if the variation is smaller than this value, it is judged that (Bv1+Bv2)/2 and an object luminance voltage Bv are equal to each other.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a focusing plate transmittance measuring device for a camera that measures the transmittance of a focusing plate. (Prior art) For example, a conventional camera has a light receiving section for photometry in the finder optical system, and the light that passes through the photographic lens and forms an image on the focusing plate passes through the focusing plate to the light receiving section. Some devices have a photometering system in which the light is incident on the light receiving section, and perform exposure control based on the photometered value from the light receiving section. (Problems to be Solved by the Invention) However, in the conventional camera described in L, the photometric value from the light receiving unit is affected by the degree of light scattering in the focus plate and the transmittance of the focus plate, so there are various problems. In a camera that can be used with interchangeable focus plates, in order to accurately control exposure based on the photometric value, it is necessary to If there is a constraint that the focus plate must be designed, and if the transparency iai of various focus plates is different, then the exposure compensation for the photometric value may be adjusted according to the transmittance of the focus plate attached to the camera. This had to be done manually, making handling of the camera cumbersome.The present invention was made by focusing on these conventional problems, and it By automatically setting the transmittance of various focusing plates, the transmittance of
In addition, even if the transmittance of various focus plates differs, it is no longer necessary to manually perform exposure compensation according to the transmittance of the focus plate attached to the camera. It is an object of the present invention to provide a camera reticle transmittance measurement device that does not require a camera reticle. (Means for Solving the Problems) The gist of the present invention for achieving the above object is to provide a focus plate (
In the focusing plate transmittance measurement device of the camera (1) that measures the transmittance of 2b), at least immediately before the mirror is raised or immediately after the mirror is down, the transmitted light of the photographing lens (1a) is transmitted through the focusing plate and measured. 171st IIl optical system (2). A second IlIII optical system (3) that measures light by reflecting the transmitted light of the photographing lens on the shutter curtain without transmitting it through the focus plate between the mirror up and the mirror down, and both the first and second light metering systems. The present invention resides in a focusing plate transmittance measurement device for a camera, characterized by comprising a calculation circuit (4) that calculates the transmittance of the focusing plate by comparing and calculating photometric values. (Function) In the focusing plate transmittance measuring device of the camera, the arithmetic circuit (4) compares the photometric value of the first photometric system (2) and the photometric value of the second photometric system (3). , to calculate the transmittance of the focusing plate. (Example) Hereinafter, an example of the present invention will be described based on the drawings. FIGS. 1, 2(a) and 2(b) show an embodiment of the present invention, and a camera focusing plate transmittance measuring device for measuring the transmittance of a focusing plate 2b attached to a camera 1 is shown in FIG. , a first photometry system 2 that measures the light transmitted through the photographic lens 1a by transmitting it through the focusing plate 2b immediately before the mirror is raised and immediately after the mirror is down; a second a optical system 3 that measures the light by reflecting it on the shutter curtain 3b without transmitting it through the focus plate 2b;
1st. It is comprised of an arithmetic circuit 4 that calculates the transmittance of the reticle 2b by comparing both photometric values of the second photometric system 2.3 and performing arithmetic operations. The first photometric system 2 includes a quick return mirror 2a. It consists of a focusing plate 2b, a pentaprism 2c, and a finder light receiving section 2d. A TTL light receiving section 3a constituting the second photometry system 3 is provided at the bottom of the camera l. The TTL light receiving section 3a is arranged at a position where it receives light transmitted through the photographing lens la and reflected by the shutter curtain 3b during photographing. Next, the arithmetic circuit 4 will be explained with reference to FIG. The finder light receiving section 2d is connected to the amplifier 5. Each is connected via a logarithmic compressor 6 to a sample and hold circuit 8.9. A release signal Sr can be input to the sample hold circuit 8, and a photographing completion signal Sf can be input to the sample hold circuit 9. Sample hold circuit 8.
9 are respectively connected to an average value circuit IO that averages the input signal. The TTL light receiving section 3a includes an amplifier 11. It is connected to a sample and hold circuit 13 via a logarithmic compressor 12. A running start signal Ss of the shutter front curtain can be input to the sample hold circuit 13. The output terminal of the average value circuit lO is connected to the middle terminal of the adder 14.
The output terminals of the sample and hold circuit 13 are respectively connected to one terminal thereof. Another middle terminal of the adder 14 has a constant shutter curtain reflectance voltage Rv. However, at another terminal, the aperture setting information voltage (Amar Avo), which is the aperture value voltage Ama minus the aperture open value voltage Avo, is
Further, a focusing plate reference transmittance voltage F is applied to each of the other terminals. The output terminal of the adder 14 is connected to a sample hold circuit 15,
It is connected to a memory 17 via an A-D converter 16. The output terminal of the memory 17 is the D-A converter 1
8 to the middle terminal of the adder 19. A focusing plate reference transmittance voltage F is applied to another middle terminal of the adder 19. The middle terminal of the comparator 20 is connected to the output terminal of the sample and hold circuit 8, and one terminal of the comparator 20 is connected to the minimum allowable light amount voltage.

[B mark A mark ◆ (F mark + ΔFV11n is applied. The middle terminal of the adder 21 is the sample hold circuit 8
, and one terminal thereof is connected to the output terminal of the sample and hold circuit 9, respectively. An absolute value circuit 22 that converts the output from the adder 21 into a feed value is connected to the output terminal of the adder 21 . One terminal of the comparator 23 is connected to the output terminal of the absolute value circuit 22, and the maximum photovoltaic variation allowable voltage ΔBvmax is applied to its terminal t. The first input terminal of the AND gate 24 receives a blank copying signal Si indicating that the blank copying period is in progress from loading the film to setting the first film. The photographing completion signal Sf is inputted respectively. The output terminal of the comparator 20 is connected to the third input terminal f of the AND gate 24, and the output terminal of the comparator 23 is connected to the fourth input terminal thereof. A sequence controller 25 is connected to the output terminal of the AND gate 24 and is activated when (1) is output from the AND gate 24 and sends a 1 operation value number to the sample and hold circuit 15 and the memory 17. The exposure control circuit 27 can be inputted with the output from the sample hold circuit 8 and the adder 19, the aperture setting information voltage (A mark A mark and film sensitivity information voltage S mark). The operation of the focusing plate transmission and rate measuring device for a camera having a camera will be explained. Before loading film into the camera l and performing the first aerial photograph, the light transmitted through the photographing lens la is photometered by the first photometry system 2. At this time, the miM light of the photographing lens 1a is
As shown in Figure (a), the light is reflected by the quick return mirror 2a and guided to the finder light receiving section 2d via the focus plate 2b and pentaprism 2c. The output of the finder light receiving section 2d is amplified by an amplifier 5 and then input to a logarithmic compressor 6. The amount of light incident on the finder light receiving section 2d is influenced by the subject brightness, the aperture opening value of the photographing lens la, and the transmittance of the focusing plate 2b. Therefore, the output voltage of the logarithmic compressor 6 is calculated using the subject brightness Bma, the aperture open value voltage Avo, the focus plate reference transmittance voltage Fma, and the focus plate transmittance correction voltage ΔFma. It can be expressed as Fma◆ΔFV].In addition, the current voltage is F, and the current voltage is F.
! It is expressed as the sum of the focus plate transmittance correction voltage ΔFma, and in the arithmetic circuit 4, Fma is constant and only ΔFma is variable. That is, since the difference in reticle transmittance between various reticle lenses is not so large, the reticle reference transmittance voltage Fma is set and the difference between the actual reticle transmittance voltage and the reticle reference transmittance voltage Fma is calculated. (By storing the focus plate transmittance correction/correction voltage ΔFV in the memory 17, the focus plate transmittance voltage can be stored with a small amount of information. When the release button is pressed to perform the it-th aerial shot, ,
The release signal Sr is sent to the sample hold circuit 8,
The sample and hold circuit 8 subtracts the aperture open value voltage from the subject brightness voltage Bvl immediately before the first aerial shot, and further adds the focus plate transmittance voltage to the value [Bvl-Avo+(Fv+
ΔFv)] is held. When the release button is pressed to perform the first aerial photograph and the quick return mirror 2a is moved to the raised position as shown in FIG. 2(b), the light transmitted through the photographing lens la is reflected by the shutter curtain 3b. is guided to the TTL light receiving section 3a,
Photometry is performed by the second photometry system 3. The output of the TL light receiving section 3a is amplified by an amplifier 11, passes through a logarithmic compressor 12, and enters a sample and hold circuit 13. The amount of light incident on the TTL light receiving section 3a is based on the subject brightness of 9. It is influenced by the aperture value of the photographing lens 1a and the reflectance of the shutter curtain 3b. Therefore, when the sample and hold circuit 13 receives the travel start signal Ss of the shutter front curtain, The value obtained by subtracting the aperture value voltage Av from the subject brightness voltage By and adding the shutter curtain reflectance voltage Rma0, that is, (BmarAma◆Rma0) is held. When the first aerial photograph is completed and the quick return mirror 2a returns to the lowered position as shown in FIG. 2(a), the light transmitted through the photographing lens la after the first aerial photograph is measured at Photometry is performed by system 2. At this time, the photographing completion signal Sf is sent to the sample and hold circuit 9, and the sample and hold circuit 9 subtracts the aperture open value voltage from the subject brightness voltage By2 immediately after the first aerial photograph, and further adds the focus plate transmittance voltage. value [By2-Avo◆(Fma+ΔFV]
hold. Then, the average value circuit 10 averages the output [Bvl-Avo◆(Fma+ΔFV1) from the sample-and-hold circuit 8 and the output [By2-Avo÷(Fma÷ΔFV1) from the sample-and-hold circuit 9, and [ (Bvl+Bv2)
/2−Avo+(Fv+ΔFv)] is output to the child terminal of the adder 14. At this time, one terminal of the adder 14 receives (B mark + Rva) from the sample and hold circuit 13, another terminal thereof receives the shutter curtain reflectance voltage Rm0, and another end r thereof receives the aperture. A setting information voltage (Amar Avo) is inputted to another terminal, and a reticle reference transmittance voltage Fv is inputted to another terminal. However, the adder 14 calculates [(Bvl+By2)/
2-Av. +(lig+ΔFv)]-(By-Av+Rvo)-F
The calculation v-(At-Avo)+Rvol is performed. Then, assuming that the average value (Bvl, By2)/2 of the subject brightness voltages Bvl and By2 immediately before and after the first aerial shot is equal to the subject brightness voltage By at the time of the first aerial shot, the adder From 14, the focusing plate transmittance correction voltage ΔF is outputted to the sample and hold circuit 15. Here, in order to judge whether (Bma10Bma2)/2 and Bma are equal or not, the amount of change in subject brightness from immediately before to immediately after the first aerial shot (Bvl and By2) is determined. difference), and calculate this amount of change and constant fi (maximum light intensity change allowable voltage ΔB
When the amount of change is smaller than the constant value, it is determined that (Bma1◆Bma2)12 and Bma are equal. This operation is performed as follows. The adder 21 receives the output [Bvl
-Avo+(Output of sample hold circuit 9 [By2-Ama0+(Fmaple ΔFV1) is subtracted from Fma0ΔFVl to eliminate the change ri(Bvl-By2) in subject brightness from immediately before to immediately after aerial shooting. It is output to the body value circuit 22. The absolute value circuit 22 converts (Bvl-By2) into a body value and outputs it as I.
BBy1By21 is output to one terminal of the comparator 23. The comparator 23 has a maximum allowable light amount change voltage ΔBvm
Compare ax and I Bvl -By21, 1Bvl
- If By21 is smaller than ΔBvmax, (1)
is output to the AND gate 24, and 1Bvl −By2
If 1 is larger than Δ13vsax, (0) is output to the AND gate 24. Since measurement and calculation cannot be performed, the comparator 20 calculates the photometric value [Bvl-Ama0÷(Fv÷ΔF
V1 and minimum light amount allowable voltage [Bmar Av0÷(Fma ÷ΔF
V] Compare with win. The comparator 20 is [Bvl-Ama0+(Fma+ΔF
When V1 is larger than [By-Avo+(Fv+ΔFv)lain (the photometric value is larger), (1) is output to the AND gate 24, and [Bvl-Avo+(Fv+ΔFv)
v)] is [Bv−Avon(Fv+ΔFv)]1111
If it is smaller, (0) is output to the AND gate 24. An output (1) indicating that (Bvl+Bma 2)/2 and Bma are equal is input to the AND gate 24 from the comparator 23, and an output (1) indicating that the photometric value is larger than above.
is input from the comparator 20, and the photographing completion signal S
F and an aerial photographing signal Si indicating that the aerial photographing period is in progress.
is input (if these four input conditions are met), the AND gate 24 sends (1) to the sequence controller 25. As a result, the sequence controller 25 is activated, and the reticle transmittance correction voltage ΔF outputted from the adder 14 at this time is held in the sample and hold circuit 15, and the activation signal is outputted from the adder 14.
After being subjected to A-D conversion in step 6, it is stored in the memory 17. The focus plate transmittance correction voltage ΔF stored in the memory 17 is converted from D to A by a DA converter 18, and added to the focus plate reference transmittance voltage F by an adder 19 to obtain the actual focus plate transmittance. Voltage (F ma ◆ ΔF, adder 1
Output from 9. In this manner, while the first aerial photographing is performed with respect to the attached reticle, the reticle transmittance correction voltage ΔF of the reticle is stored in the memory 17. In actual shooting, each parameter necessary for exposure control, namely film sensitivity information voltage Sv, aperture setting information voltage (A
[B ma1 - A ma O◆ (F ma ◆ΔF ma month), which is the output of sample hold 8, and the actual focusing plate transmittance voltage (F ma ΔFV is input to the exposure control circuit 27, and exposure control is performed based on the light transmitted through the focus plate 2b. In the first embodiment, the photometry value of the first photometry system 2 immediately before and after the first exposure is The average value of and the second photometric system 3
The transmittance of the focusing plate 2b is measured from the photometric value of the first photometric system 2 and the photometric value of the 211th optical system 3 immediately before or after the above-mentioned aerial photography.
The transmittance may be measured. In addition, in the first embodiment of the present invention, the sample hold circuit 13
The shutter front curtain running start signal Ss is input to the shutter front curtain, and the photometric value of the reflected light from the shutter front curtain is sampled and held by the circuit 1.
3, but the shutter front curtain running start signal Ss
Alternatively, by inputting the shutter trailing curtain travel completion signal to the sample hold circuit 13, the photometric value of the reflected light from the shutter trailing curtain can be held in the sample hold circuit 13, and the focusing plate transmittance can be calculated. It is possible. (Effects of the Invention) According to the camera focus plate transmittance measuring device according to the present invention,
At least immediately before the mirror is raised or immediately after the mirror is down, the light metering value of the first photometry system is measured by transmitting the light transmitted through the photographic lens through the reticle, and between the time when the mirror is raised and the mirror is down, the light transmitted through the photographic lens is measured. The arithmetic circuit is configured to automatically calculate the transmittance of the focus plate from the photometric value of the second photometry system, which measures light by reflecting it off the shutter curtain without transmitting light through the focus plate, so it can be used with various types of cameras attached to the camera. This eliminates the constraint of having to design reticle lenses so that their transmittances are uniform, and even when various reticle lenses have different transmittances, it is possible to There is no need to manually make exposure compensation according to the transmittance, making it easier to handle the camera.

[Brief explanation of drawings]

1, 2(a) and 2(b) show an embodiment of the present invention, FIG. 1 is a circuit diagram of a focusing plate transmittance measuring device according to an embodiment, and FIG. 2(a) ) and (b) are longitudinal sectional views of a camera to which the circuit of FIG. 1 is applied.

Claims (3)

[Claims] (1) In a camera focus plate transmittance measuring device that measures the transmittance of a focus plate, the first photometry meter transmits light from the photographing lens through the focus plate at least immediately before the mirror is raised or immediately after the mirror is lowered. a second photometry system that measures light by reflecting the light transmitted through the photographing lens on a shutter curtain without transmitting it through a focus plate between mirror up and mirror down; and both the first and second photometry systems. 1. A focusing plate transmittance measurement device for a camera, comprising a calculation circuit that calculates the transmittance of a focusing plate by comparing and calculating photometric values. (2) In the device according to claim 1, the arithmetic circuit calculates an average value of the photometric value of the first photometric system immediately before the mirror is raised and the photometric value of the first photometric system immediately after the mirror is lowered. and a photometric value of the second photometric system to measure the transmittance of the focusing plate. (3) In the apparatus according to claim 2, the arithmetic circuit converts the actual reticle transmittance to a constant reticle reference transmittance (reticle reference transmittance voltage F_V and reticle transmittance correction value). A focusing plate transmittance measuring device for a camera, characterized in that the focusing plate transmittance correction value is expressed as a sum of a focusing plate transmittance correction voltage ΔF_V, and the focusing plate transmittance correction value is calculated from the average value and the photometric value of the second photometric system. .