JPH01267620A - Exposure control device of camera - Google Patents

Abstract

PURPOSE:To obtain the exposure control device of a camera which is increased in the probability of obtaining a correct exposure by executing exposure correction in accordance with the conditions having no relation with the absolute values of the respective metered values obtd. by multipoint metering. CONSTITUTION:An exposure correcting means 3 which corrects the control brightness value VBT for exposure control with the correction value determined in accordance with the prescribed conditions having no relation with the absolute values of the metered values BVc, VB0 by respective metering means 1, 2 is provided. The prescribed conditions having no relation with the absolute of the respective metered values BVc, VB0 consist of, for example, a subject distance D or the focal length (f) of a photographing lens, photographing magnification beta(=f/D), or difference DELTABV0C(BV0-VBC) or the combination thereof. The correction value is subtracted from the metered values in the metering area on the low brightness side in such a manner that the metering error is offset, even if the metered values include the metering error as said values are affected by the brightness of the metering area on the adjacent high brightness side. The correct control brightness value is thereby obtd. and the probability that the optimum exposure control is executed is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an exposure control device for a camera having a plurality of photometry areas.

[Prior Art] Conventionally, in an exposure control device for a camera having multiple photometry areas, there has been an evaluation photometry method in which an appropriate control brightness value is calculated by calculating a weighted average of the photometry values obtained in each photometry area. is proposed.

The coefficients (weighting coefficients) multiplied by each photometric value include zero,
Therefore, the control brightness value is a value between the maximum and minimum photometric values obtained in each photometric area.

In addition, in such an evaluation metering method, it has been proposed to prepare a plurality of calculation formulas for the weighted average in advance and to switch the calculation formula to be used depending on the photographing magnification (Japanese Patent Laid-Open No. 61-279829). reference).

[Problems to be Solved by the Invention] In an exposure control device for a camera having a plurality of photometry areas, how can a control brightness value for exposure control be determined from photometry values obtained in a plurality of photometry areas? The question is whether optimal exposure can be obtained. Japanese Patent Publication No. 61-27982
In Publication No. 9, based on the understanding that the optimal control brightness value can be obtained by properly weighted averaging of each photometric value, the weighted average formula for calculating the control 69 brightness value from each photometric value is applied to the photographing magnification. By switching accordingly, we are attempting to perform appropriate exposure control.

However, according to the results of repeated actual shooting assuming various shooting scenes with different brightness distributions while changing the subject distance, focal length of the photographic lens, photographing magnification, etc., the optimal control brightness value is determined by weighting each photometric value. It is not always determined by averaging, but rather is often obtained by applying exposure compensation to the photometric value, which is determined based on conditions unrelated to the absolute value of the photometric value.Especially in backlit scenes, the brightness of the peripheral area is If the brightness is +1.5 to 2.5 EV brighter than the center brightness, the optimal control brightness value may not exist between the maximum and minimum photometric values obtained in each photometric area.
The above-mentioned conventional technology has a problem in that it is not possible to perform optimal exposure control in such a shooting scene.

The present invention has been made in view of these points, and its purpose is to perform exposure compensation based on conditions unrelated to the absolute value of each photometric value obtained by multi-point photometry. An object of the present invention is to provide an exposure control device for a camera that increases the possibility of obtaining proper exposure.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in the figure, a first photometer 1 measures a first area A1 within a photographic screen S, and a second photometer measures a second area A2 at least partially bordering the first area A1. In the camera exposure control device comprising at least the photometering means 2, the photometry value BVc by each photometering means 1.2
, BVo is characterized in that an exposure correction means 3 is provided for correcting the control brightness value BVT for exposure control with a correction value determined based on a predetermined condition unrelated to the absolute value of BVo.

Here, the predetermined conditions that are unrelated to the absolute values of the photometric values B V c and B V o include, for example, the subject pressure MD, the focal length f of the photographic lens, the photographic magnification β (=f/D), and the photometry Difference in value ΔB Voc (= B Vo − B Vc)
or a combination of these.

[Function] Now, as shown in Fig. 1, the shooting screen has a spot photometry area A1 at the center and a wide photometry area A at the periphery.
Regarding the case where it is divided into two.

The present invention will be described in detail. A photometric value BVc of central brightness obtained by the first photometric means 1 and a photometric value BV of peripheral brightness obtained by the second photometric means 2.

When the relationship is BVe#BVo, it is the same as when performing average metering, and there is no need to perform exposure compensation, but BV
When c<BVo, the photometric value BVc of the center brightness is influenced by the peripheral brightness and includes a photometric error that is larger than the true central brightness, and when BVc>BVo, the photometric value BVo of the peripheral brightness is influenced by the center brightness. This includes a photometric error that is larger than the true ambient brightness.

Here, as shown by the solid line in Figure 1, when the photometric area A2 at the periphery is sufficiently wider than the photometric area AI at the center, the influence of the center luminance on the photometric value BVo of the peripheral luminance is small and the photometric error is ignored. Although it may be possible in some cases, as shown by the broken line in the same figure, if the photometric area A2' at the periphery is slightly wider than the photometric area A2 at the center, the center luminance will be The influence becomes so large that the photometry error cannot be ignored.

Photometry area A1. In a normal camera where the size of A2 is constant, the magnitude of the photometry error mentioned above is determined by, for example, the subject pressure ID, the focal length f of the photographing lens, and the photographing magnification β<=
r, ・'D), difference in photometric values ΔBVoe (=BVo−B
Vc) or a combination thereof. Therefore, the exposure correction means 3 sets in advance a correction value that cancels out the photometry error according to various photographing conditions, and the photometry (ti B V e , B
By subtracting a correction value from Vo so as to offset the photometric error, an appropriate control brightness value B V y is obtained.

[Example] FIG. 2 is a schematic configuration diagram of a photometric optical system in a single-lens reflex camera to which the present invention is applied. The subject image reflected by the subject mirror M and formed on the focal plane FP of the focusing plate FS becomes an erect image via the pentaprism pt, and is observed through the eyepiece EP. eyepiece l
The photometric lens L placed near the / lens EP has a focal plane F.
P and the light-receiving surface of the photometric element SPD are configured to be conjugate, and a photographed screen imaged on the focal plane F P is projected in a reduced size onto the photometric element SPD. The photometric element SPD is
A plurality of photometric elements S P D i (i” 1, 2, ・
), the shooting screen is divided into multiple photometry areas, and photometry values can be obtained individually for each photometry area.

Fig. 3 (1) is an example in which the photometry area in the photographic screen S is divided into two parts: a photometry area A1 in the center and a photometry area A2 in the periphery. Let each of the 0-divided portions corresponding to areas Al and A2 be a photometric element 5PD1.5PD2. In addition, the BV values obtained by converting the photometric values obtained with each photometric element 5PDI and 5PD2 to the Apex system are BVc and B, respectively.
V.

Figure 3(b) shows A- in the photographic screen shown in Figure 3(a).
It is ideal for the photometric sensitivity distribution to be as shown by the broken line, which shows the photometric sensitivity distribution of photometric element SPD 1 on the A' edge line, but in reality it is due to aberrations of the photometric optical system, flare, and photometric element 5PDI. Some blurring may occur due to its own leakage current, etc.
The photometric sensitivity distribution is as shown by the solid line. Now, it is assumed that among the photometric sensitivities of the photometric element 5PDI, the integral value of the sensitivity within the photometric area A1 (the intersecting hatched area in Fig. 3(b)) is 80% of the integral value of the entire sensitivity. . At this time, if the photometric area A2 at the periphery of the shooting screen is -4EV brighter than the photometric area A1 at the center, the photometric value BVo obtained by the photometric element 5PD2 is the photometric area A2.
However, the photometric value BVc obtained by the photometric element 5PDI is influenced by the brightness of the photometric area A2, and becomes +2EV brighter than the true brightness of the photometric area A1 (see Fig. 3). c).

Note that the photometry area A2 at the periphery is the photometry area A2 at the center.
When it is darker than 1, the same thing should happen with the photometric value BVo of the peripheral brightness, but in reality the photometric element 5PD2 at the periphery has a wider area than the photometric element 5PD1 at the center, so the photometric area It is not easily affected by the brightness of A1.

Therefore, below, only the influence of the peripheral brightness on the photometric value BVe of the center brightness will be considered.

(i) When the photographing magnification β is changed In Fig. 4 (a) to (c), the photographing magnification β is 1/1, respectively.
5. The human image in the case of 1150.1/80 is
The figure is shown in parentheses (,). As shown in the figures above, when the shooting magnification β of the main subject is larger than 1/100, there is a high probability that the main subject is about the size of a person, and when focusing, the main subject will be near the center of the screen. is common. In the case of a backlit scene, that is, when the luminance of the main subject such as a person is lower than the surrounding luminance, when the photographing magnification β is high and the main subject is larger than the photometry area A1, as shown in Fig. 4(a), The amount of influence of the surrounding brightness on the photometric value BVc of the center brightness is small. Therefore, when the imaging magnification β is high, the correction value for the control brightness value may be small. However, as shown in FIG. 4(e), 9. At a small shooting magnification where the main subject barely covers the photometric area A1, due to the blurring effect of the photometric sensitivity described above, the photometric value BVc of the center brightness is influenced by the bright peripheral brightness, and becomes lower than the true brightness of the main subject. It also becomes more expensive. Therefore, when the imaging magnification β is low, it is necessary to increase the correction value for the control brightness value. Also, the fourth
[As shown in M(b), in the case of the above-mentioned intermediate imaging magnification, the correction value for the control luminance value must also be set to an intermediate value.

(ii) When changing the photometric value difference ΔBVoc The amount of influence of peripheral brightness on the central brightness photometric value BVc is the difference ΔB Voe (= B Vo − B Vc). In the photometric element 5PD1 having the photometric sensitivity distribution as shown in FIG. 3(b), ΔBVoc=
When the value is about 1.5 to 2.5, the photometric value BVe of the center brightness
is most affected by ambient brightness. Therefore, ΔB
When Voc is within this range, it is necessary to set a large correction value for the control brightness value. Also, ΔB Voc>
2 and 5, the main subject is considered to be larger than the person and includes the entire photometry area A1, so the photometric value BVc of the center brightness captures the main subject's brightness almost accurately. I can say that there is. Therefore, ΔBvo
When c is larger than 2.5, it is necessary to set a small correction value for the M pancreaticity value.

When ΔBVoc<1, it is considered that there is hardly any backlighting, so it is considered that there is no need to correct the control brightness value. Further, when ΔBVoc is in the range of 1 to 1.5, it is necessary to set the correction value for the control brightness value smaller than when ΔBVoc is in the range of 1.5 to 2.5.

If the correction value for the 1tiII control brightness value is set according to the conditions exemplified in (i>, (ii) above, the possibility of obtaining the optimum exposure will increase. A specific example of a hardware and software configuration suitable for performing exposure control will be described.

FIG. 5 is a block circuit diagram of a camera to which the present invention is applied. In FIG. 1, SI is a photometry switch, S2 is a release switch, and the former is turned on by the first stroke of the shutter button (not shown). The latter is turned on by the second stroke of the shutter button. One end of each switch Sl, S2 is connected to the ground level, and the other end is connected to the microcomputer 10.
input ports) are connected to IPl and IF5, respectively. 1
1 is a logarithmic compression circuit, and the photometric element 5PDI of the camera,
The photometric values obtained by 5PD2 are logarithmically compressed to obtain the photometric values B V c , B V corresponding to the BV values of the Apex system.
Output each o. Although the output of the logarithmic compression circuit 11 is an analog signal, it is converted into a digital signal by the A/D converter 12 and input to the microcomputer 10. 13 is a lens ROM built into the photographic lens.
It stores information such as the focal alternation layer f of the lens,
This lens data can be input to the microcomputer 10.

Reference numeral 14 denotes a distance measuring circuit that measures information regarding the subject's distance MD and inputs it to the microcomputer 10. 15
is an aperture control mechanism, which controls the aperture of the photographing lens based on the data of the aperture value AV output from the microcomputer 10. 16 is a shutter system ms clear,
Exposure time TV output from microcomputer 10
control the shutter speed based on the data.

FIG. 6 is a flowchart showing the contents of a program executed by the microcomputer 10. However, parts not directly related to exposure calculation are omitted. When the photometry switch S is turned on, the microcomputer 10 executes the process from #100.

First, to outline the main processing flow, in #100, the photometric value BVe of the center brightness and the photometric value BVo of the peripheral brightness are
Enter each. In #200, the photometric value BVc of the center brightness is corrected to obtain the true center brightness BVc'. In #300, the photometric value BVo of the peripheral brightness is corrected to obtain the true peripheral brightness BVo'. In #400, the control brightness value B■T is determined based on the true center brightness BVc' and the true peripheral brightness BVo''. In #500, the aperture value A'V and the exposure are determined based on the control brightness value BV. time tv
Determine.

Next, the contents of each process will be explained in detail.

In #100, the photometric value BVc of the center brightness and the photometric value BVo of the peripheral brightness are respectively input. For that reason, #110
Now, the photometric element 5PD corresponding to the photometric area A1 in the center
The output of I and the output of the photometric element 5PD2 corresponding to the peripheral photometric area A2 are each converted into an apex-based BV value by the logarithmic compression circuit 11, and the analog values are converted to the A/D.
The signal is converted into a digital signal by the 2t11 circuit 12 and input to the microcomputer 10.

In #200, the photometric value BVc of the center brightness is corrected to obtain the true center brightness BVc'. For that reason, #2
10, the photometric value BVc of the center brightness and the photometric value B of the peripheral brightness
Difference from Vo = BV.

- Find BVc. If ΔBVoc is larger than +IE■, it can be said that there is a backlight condition. In this case, the photometric value BVc of the central brightness is influenced by the peripheral brightness and is different from the true central brightness BVc. Therefore, in step #220, a correction value α that cancels out the influence of peripheral brightness is determined. Specifically, first, the focal length f of the photographing lens is stored in the lens ROM 13.
The photographing magnification β is obtained by inputting information regarding the subject distance from the distance measuring circuit 14 to the microcomputer 10 and calculating β=f/D. The difference ΔBVoc between this photographing magnification β and the above-mentioned photometric value
Using
1150. ΔBVoc=2. If OEV, α=0.
It will be 75. This correction value α is determined by the above-mentioned <i), (ii)
It is determined to cancel out the influence of ambient brightness depending on the conditions. In #230, by subtracting the correction value α from the photometric value BVc of the center brightness, the influence of the peripheral brightness is canceled out, and the true center brightness BVc' is obtained.

Table 1 In Table 1, when the imaging magnification β is smaller than 1/100, α=O. This is β<1/100
This is because the main subject is often larger than the photometric area A1 at the center, and correcting the photometric value BVc of the center brightness may result in erroneous photometry since it is often a landscape photograph or the like.

Note that, like the distance measuring circuit 14 using the TTL phase difference detection method,
In the case of a focus detection circuit that calculates the amount of lens extension according to the amount of defocus, the shooting distance X and the focal length f of the photographing lens are
You can also calculate the shooting magnification β by calculating β=x/r from , since the focal length f is fixed, it goes without saying that the correction value α may be calculated using only the subject pressure HD or the lens extension amount X when the subject is in focus, instead of the imaging magnification β.

In #300, the photometric value BVo of the peripheral brightness is corrected to obtain the true peripheral brightness BVo'. In other words, when BVo<BVc, the photometric value BVo of the peripheral brightness must be influenced by the central brightness, so it is necessary to make a correction to offset that influence.
), the area of the photometric area A2 at the periphery is considerably wider than the photometric area A1 at the center, so the influence of the center luminance can be ignored. Therefore, in #310, the photometric value BVo of the peripheral brightness is set as the true peripheral brightness BVo'.

In #400, the true center brightness BVc' and the true peripheral brightness B
A control brightness value BV is determined based on Vo'. Therefore, in #410, the true center brightness BVc after correction is
” and the true peripheral brightness BVo' ΔB Voc' =
Find B Vo' - B Vc'. In #420, it is determined whether the difference ΔBVoc' is 2EV or less.

If ΔBVoc'>2, it means that the true peripheral brightness BVo' is +2 EV brighter than the true central brightness BVc'', so it is determined that there is a backlight condition, and #43
0, the true center brightness BVe' is set as the control brightness value BVT.

This makes it possible to provide optimal exposure for the main subject. If ΔBVoc'≦2, it is determined that there is no backlight condition, and in #440, the center brightness BVc'' and the peripheral brightness B
Let the arithmetic mean with Vo' be the control brightness value BV. This is because the center brightness BVc' may vary due to shaking of the main subject, etc., so instead of just using the center brightness BVc',
By taking the average with the surrounding brightness BVo', photometry can be performed over a wide range. However, since the photometry area A1 at the center is considerably narrower than the photometry area A2 at the periphery, average photometry is performed in a centered manner.

In #500, the aperture value AV and exposure time TV are determined based on the control 61IyR degree value BVT. Specifically, since this embodiment uses a TTL (radiometry) photometry optical system as shown in FIG. and add the film sensitivity SV to obtain the control exposure value EV [=
The aperture value AV and exposure time TV are determined so that AV+TV=E■.

FIG. 7 is a flowchart showing the operation of another embodiment of the present invention.9 In this embodiment, the same step numbers are given to the parts corresponding to the embodiment of FIG. 6, and duplicate explanations are omitted. In this embodiment, the range in which the correction value α is set to O when the focal pressure 1r of the photographing lens is 35 m- or less is widened, and flash photography is taken into account when calculating the control brightness value BV. This is different from the embodiment shown in FIG. Hereinafter, only these differences will be explained.

In this embodiment, after determining the correction value α in #220, #2
21, it is determined whether the focal length r of the photographing lens is 35+am or less and the photographing magnification β is smaller than 1/60. If the conditions of f≦35+us and β<1/60 are satisfied in #221, the correction value α is forcibly set to 0 in #222.
shall be. This is because when the focal length f is 35 o++ m or less, there is a high probability that it will be a landscape photograph even if the photographing magnification β is relatively large.
The correction value α is set to 0 even in the range of 1/100≦β<1/60.

Further, in the process #400L[i for determining the alvi degree value BVT, it is determined in #411 whether the flash switch swFL (not shown) is turned on.

When the flash switch 5WFL is OFF, steps #420 to #440 are performed in the same manner as in the embodiment shown in FIG. 6, and the routine proceeds to the natural light exposure control routine in #600.

When the flash switch swFL is turned on, automatic flash photography is performed when the brightness is low or when there is backlight. Therefore, in #412, the center brightness BVc' is set to 6E.
It is determined whether or not it is less than V. If BVc'<6, it is determined that the main subject has low brightness, and #414
Set the control brightness value to B VT = B Vc' + 1,
At #700, the process moves to a flash exposure control routine. This means that the aperture value AV and shutter speed TV are controlled so that the main subject is underexposed in IE ■ with only natural light. The lack of light intensity for the main subject is then compensated for by the flash.

If BVc'≧6, it is determined that the main subject is not of low brightness. In this case, in order to determine whether or not it is a backlit state, center brightness BVc' and peripheral brightness BVo'
The difference ΔB Voc' (= B Vo' - B Vc
' ) is larger than 2.5 or not is determined in #413. If ΔBVO(!'≦2.5, it is determined that the main subject is not in a backlit state, and steps #420 to #440 are performed in the same manner as in the 60th embodiment, and the natural light exposure control routine is executed in #600. 6Δ13V oc'>
2 5′? 'In some cases, the main subject is backlit t': Determined! 12. Set the control brightness value to BV r in #415.
= L', Vo'-1 and 15, #700'Fura...
? Gino moves into the exposure control routine. ,: The background is overexposed in IEV and the main subject in I-1 is (ΔB Voc'
-1) Means underexposure of EV. The lack of light for the main subject is captured by the flash, so both the main subject and the background can be placed within the film's depth, and the main subject is properly exposed by the flash. The IEV overexposes the front vertical image, resulting in a photograph that appears to be in a backlit situation.

FIG. 8 shows the application of the present invention to a camera using multi-point distance measurement and multi-point photometry.1. 3 shows an example of dividing the shooting screen S in the case of
Two spot photometry areas A3゜A4. The photometric value of the photometric element corresponding to A5 is converted to Apex system 7':
Let the B V values be B −V X, BVy, and BVz. In addition, these photometry areas A3. A4. The BV value obtained by multiplying the photometric value of the photometric element corresponding to the photometric area A6 that measures a wide area around A5 by 9 #Q to the apex system is set as the photometric value BVo of the peripheral brightness. The distance measurement circuit 14 has a photometry area A3. A
4. That of A5-,! ′? The photometry area A3. A4. It is assumed that one of the areas A5 and 17 is selected as the focus determination area. Photometric value B Vx.

Among BVy and BVz, BV[ of the photometry area selected by the distance measuring circuit 14 is taken as the photometry value Bc of the center brightness, and as in the previous embodiment, the photometry value difference ΔBVθC and the photographing magnification β are used. The correction value α is determined, and by subtracting the correction value α from the photometric value BVe, the true central brightness BVe is determined.
' can be found.

[Effects of the Invention] As described above, the present invention includes a first photometry means for photometering a first area within both photographic surfaces, and a second area that at least partially borders the first area. In the exposure control device of the camera, the control brightness value for exposure control is corrected with a correction value determined based on a predetermined condition that is independent of the absolute value of each photometric value. Since the correction means is provided, even if the photometry value in the low-brightness side photometry area contains a photometry error due to the brightness of the adjacent high-brightness side photometry area, this photometry error can be canceled out. By subtracting the correction value, an appropriate control brightness value can be obtained and the possibility of optimal exposure control is increased.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the basic configuration of the present invention, Figure 2 is a schematic diagram of the 3vI optical system of a camera as an embodiment of the present invention, and Figure 3 (a) is a diagram of the same camera as above. Figure (b) is a diagram showing the photometric brightness distribution of the photometric element used in the same camera, Figure (c) is a diagram showing the photometry error in the same camera. Explanatory diagram for, 4th
Figures (a) to (c) are diagrams showing the relationship between the main subject and the photometry area at different photographing magnifications in the same camera as above, and Fig. 5 is a schematic circuit configuration of the same camera as above. Block circuit diagram shown,
FIG. 6 is a flowchart for explaining the operation of the same camera as described above, FIG. 7 is a flowchart for explaining the operation of another embodiment of the present invention, and FIG. 8 is a flowchart for explaining the operation of another embodiment of the present invention. FIG. 3 is a diagram showing an example of division. 1 is a first photometry means, 2 is a second photometry means, and 3 is an exposure correction means.

Claims (9)

[Claims] (1) A camera that includes at least a first photometer that measures a first area within the photographic screen, and a second photometer that measures a second area that at least partially borders the first area. The exposure control device is characterized by being provided with an exposure correction means for correcting a control brightness value for exposure control with a correction value determined based on a predetermined condition unrelated to the absolute value of the photometry value by each photometry means. Camera exposure control device. (2) The camera exposure control device according to claim 1, wherein the predetermined condition is a subject distance. (3) The camera exposure control device according to claim 1, wherein the predetermined condition is a focal length of a photographic lens. (4) The exposure control device for a camera according to claim 1, wherein the predetermined condition is a photographing magnification. (5) The exposure control device for a camera according to claim 1, wherein the predetermined condition is a difference between photometric values obtained by the first and second photometric means. (6) The exposure compensation means is configured to
5. The exposure control device for a camera according to claim 4, further comprising means for increasing the correction value continuously or stepwise as the photographing magnification decreases. (7) The exposure control device for a camera according to claim 5, wherein the exposure correction means is a means for setting a maximum correction value for a fixed value or a fixed range of differences in photometric values. (8) The exposure control device for a camera according to claim 1, further comprising a correction prohibition means for prohibiting correction by the exposure correction means under a predetermined prohibition condition. (9) The camera exposure control device according to claim 8, wherein the predetermined prohibition condition is when the focal length of the photographing lens is equal to or less than a predetermined value and the photographing magnification is equal to or less than a predetermined value.