JPH01304435A - Exposure controller - Google Patents

Abstract

PURPOSE:To inhibit photographing when it is out of a controllable exposure range by measuring distances between a stroboscope and an object and between the stroboscope and a reflector and reflectance and obtaining an appropriate exposure value. CONSTITUTION:A 1st range-finding part 40 which measures the object distance La, a 2nd range-finding part 42 which measures the reflector distance Lb and a reflectance measuring part 44 which measures the reflectance (n) of the reflector have common or individual light position elements and outputs therefrom are inputted in a diaphragm value arithmetic operation circuit 46 to obtain the appropriate diaphragm value FNo. A diaphragm control mechanism 50 controls a diaphragm blade 52 until an output from a diaphragm value encoder 54 becomes to coincide with the diaphragm value FNo so as to perform the control of exposure at the time of photographing with indirect lighting. When the diaphragm value FNo is out of the range of 'open stop value'-'minimum diaphragm value', the circuit 46 can not perform control and a warning is given with a lamp and a buzzer, etc., through a warning/inhibition part 56 to inhibit the action of the mechanism 50 or perform release lock, etc. Thus, the appropriate exposure can be accurately controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a bounce strobe with a variable irradiation angle.
In particular, it relates to the exposure control device.

[Conventional technology]

Generally, strobes are built into the camera or connected to the camera via a hot shoe.

Therefore, when photographing is performed by directly irradiating illumination light toward a subject, a so-called red-eye phenomenon may occur because the distance between the light emitting part of the strobe and the optical axis of the photographing lens is small. Furthermore, in the case of direct irradiation, if there is a wall behind the subject, the shadow of the subject will appear on the wall, and the shadow will also appear in the photograph.

As a countermeasure against these problems, there is indirect irradiation using a bounce strobe. Since the irradiation angle of a bounce strobe is variable, the strobe is emitted toward the ceiling or wall, and the reflected light is used to indirectly illuminate the subject to take pictures.

Conventional exposure control methods for indirect illumination include integrating the reflected light from the subject and stopping the flash when the integrated value reaches a predetermined value, and firing a test flash using an incident light type flash meter. There was a method to find the appropriate aperture value from

[Problem to be solved by the invention]

The former method of integrating the reflected light from the object does not take into account the reflectance of the object, so the integral value is affected by the reflectance. Therefore, if the subject is white,
Since its reflectance is higher than the standard reflectance, the time it takes to complete the integration is short, resulting in an exposure amplifier, which makes white appear grayish. Conversely, if the subject is black, its reflectance is low, so it takes a long time to complete the integration.
The image is overexposed, and black appears grayish.

The latter method of firing a test flash requires the preparation of a special measuring device called an incident light type flash meter, and is not suitable for general photography.

This invention was made to deal with the above-mentioned circumstances,
To provide an exposure control device with a simple configuration that can always appropriately control exposure during indirect irradiation photography using a bounce strobe, regardless of the reflectance of a subject.

[Means to solve the problem]

The exposure control device according to the present invention includes a measurement unit that measures the distance between the strobe and the subject, the distance between the strobe and an object that reflects light from the strobe toward the subject, and the reflectance of the object;
The camera includes an arithmetic circuit that calculates an appropriate exposure value from these measured values, and a warning/prohibition unit that issues a warning or prohibits photography if the appropriate exposure value is outside the controllable exposure range of the camera.

[Effect]

According to this invention, the actual optical path length of the light from the strobe during indirect irradiation is determined from the distance between the strobe and the subject and the distance between the strobe and the reflective object, and the reflectance of the object and the guide nanometer for direct irradiation are determined. If the appropriate exposure value for indirect illumination found from these is outside the camera's controllable exposure range, a warning will be issued or photography will be prohibited, allowing you to control the exposure. Inappropriate photography can be prevented.

〔Example〕

Embodiments of an exposure control device according to the present invention will be described below with reference to the drawings.

In general, the appropriate aperture value FN for flashmatic photography
o is the strobe's guide number GN, and D is the subject distance.
Then, it is expressed as follows.

GN-FNo-D-(1
) Figure 1 shows a conceptual diagram of indirect irradiation. In the case of indirect irradiation,
Since the light from the strobe reaches the subject 12 after being reflected by the reflective object 14, the subject distance in equation (1) is not the distance MLa between the strobe 10 and the actual subject 12, but the distance between the strobe 10 and the virtual subject 12. Distance Lc from 12a
It is. Here, both the distance between the actual subject 12 and the reflective object 14 and the distance between the virtual subject 12a and the reflective object 14 are distances Lb. The distance Lc is expressed as follows.

L c - L a / c o sθ ・
(2) -2Lb/sin θ -(2a) The irradiation angle θ during indirect irradiation of the strobe 10 is expressed as follows from La and Lb.

θ-tan' (2Lb/La) -(3)
Further, the guide number GNn for indirect irradiation is obtained by multiplying the guide number GNo for direct irradiation by the reflectance n (ratio of reflected energy to predetermined incident energy) of the reflecting object, and is expressed as follows.

The guide number GNo in the case of direct irradiation is determined in advance.

G N n = Ji X G N o
-(4) By substituting Lc in equation (2) or equation (2a) for D in equation (1) and GNn in equation (4) for GN in equation (1), indirect irradiation can be performed. Appropriate aperture value FN
o is expressed as follows.

When formula (2) is substituted: F No − G N n / L c−fTxGNo
xcos θ+La -5X G No + La Xcos 1jan' (2L b/ La) l-
(5) When formula (2a) is substituted: F No -G N n /L c-5XGNox
sinθ÷2Lb −(';; x c, N O+ 2 L bXsin
fjan' (2L b/L a) l - (6) In other words, from equation (5) or equation (6), the appropriate aperture value FNo for indirect illumination is the subject distance La, the reflective object distance Lb, and the reflectance of the reflective object. n and guide number (during direct irradiation) GN
It can be found from o. Since the guide number (during direct irradiation) is known, the appropriate aperture value FNo.
In order to find the object distance La, the reflective object distance Lb
.

It is only necessary to know the reflectance n of the reflective object.

Next, how to obtain the subject distance La, the reflective object distance Lb, and the reflectance n of the reflective object will be explained. Here, a method using a PSD (optical position detection device) will be explained.

FIG. 2 is a diagram showing the cross-sectional structure of the PSD.

PSD is a high resistivity layer on the surface of a high resistivity n layer (1 layer).
It has a structure in which n slave stations with a high resistivity layer are arranged on the back side of the ``'' layer. Among the electron-hole pairs generated when a light spot is irradiated on one point Q on the PSD surface, the gearia that has reached the p-n junction is taken out from the light incident point Q in the p-layer of the high resistivity layer and sent to the electrodes A and B. Divide each electrode in inverse proportion to the distance to A.

taken out from B. Therefore, the position of the light incident point Q can be determined from these current values.

Carriers generated in the semiconductor by the incidence of a light spot are drifted by the electric field in the depletion layer, and holes reach the p- layer and electrons reach the n-layer (i-layer). The holes injected into the p-layer are divided into components flowing through resistors R1 and R2, and currents II and I2 are generated.
It is taken out from electrodes A and B as.

The distance from the midpoint of electrodes A and B to the light incident point Q is X1 point Q
If the resistance from point Q to electrode A is R1, the resistance from point Q to electrode B is R2, the distance between electrodes A and B is Ω, and the resistance between electrodes A and B is Rp, II.

I2 is expressed as follows.

11- (R2/Rp) Io...(7
)I2=(R1/Rp)To...(8)1
o-11+I2-(9) If the distribution of resistivity of the surface resistance layer is uniform, resistances R1 and R2 are proportional to the distance from point Q to electrodes A and B and can be expressed as follows. .

R1-(Rp/2)fl+ (2X/1))l...(
10) R2-(Rp/2)[1-(2X/42))・
...(11) By substituting equations (10) and (11) into equations (7) and (8), the following relationship is obtained.

1 1 = (1/2)fl - (2X/R)11
.

... (12) 12- (1/2)II + (2X/R month■0...
(13) Here, in order to detect X without being affected by the position of the light incident point Q and the value of the current Io, if X is expressed as the ratio of the output current II, 12 by the following normalization calculation good.

(12-11)/ (I2+I 1) = (Ω/2)・X ... (14) (1
4) From equation 4, it can be seen that the input 1
=1 Position X can be known.

FIG. 3 is a diagram showing the principle of determining the distance Mj using such a PSD.

A PSD 38 and an infrared light emitting element 30 such as an I RED are placed apart from each other by a baseline length S, and the I RED 30,
Focal length above D38/! /l f (1) > 7:
32.

36 are provided respectively. Here, lens 36 and PSD3
The interval between 8 and 8 is f.

If the distance to the object to be measured 34 is L, and the amount of change in the current value of electrodes A and B of the PSD 38 when the I RED 30 is turned on is 11.12, the distance from equation (14) is as follows. can be asked for.

L-5-f/X -5-f・(2/Ω)・f(12-11)/(12+11)! (15) Here, since S, f, and Ω are constants, L can be obtained only from the PSD current changes all and I2.

Also, the sum of the amount of current change when IRED is turned on is 1 o
-I 1. + I 2 is a value proportional to the reflectance n for the wavelength of I RED. That is, 1o-11+l2 clcn - (16) thus, the output current of the PSD)1. Subject distance L from I2
a % reflective object distance Lb and the reflectance of the reflective object can be determined.

FIG. 4 is a block diagram of the first embodiment.

A first distance measuring section 40 that measures the object distance La, a second distance measuring section 42 that measures the reflective object distance Lb, and a reflectance n of the reflective object.
The output of the reflectance measurement section 44 that measures the aperture value calculation circuit 4
6 is input. The first distance measuring section 40, the 211111th distance measuring section 42, and the reflectance measuring section 44 need to have PSD,
The second distance measuring section 42 and the reflectance measuring section 44 only need to have a common PSD.

Furthermore, the first and second distance measuring sections 40 and 42 may not have their own PSDs, but may be common to the PSD for the autofocus circuit.

The aperture value calculation circuit 46 calculates the appropriate aperture value FNo according to equation (5) or equation (6). Since this calculation is complicated, a table based on La, Lb, and n may be prepared and calculated from this.

The obtained appropriate aperture value data FNo is determined by the aperture control mechanism 50.
is input.

The aperture control mechanism 50 adjusts the aperture blades IJI 5 until the output of the aperture value encoder 54 matches the appropriate aperture value data FNo.
Control 2. This makes it possible to control exposure during indirect irradiation photography.

The aperture value calculation circuit 46 includes an open/minimum aperture value input section 48;
A warning/inhibition section 56 is also connected. The open/minimum aperture value input section 48 supplies the aperture value and the minimum aperture value of the aperture blades 52 to the aperture value calculation circuit 46 .

When the aperture value of a zoom lens changes due to zooming, the input value changes accordingly.

The appropriate aperture value FN obtained by the aperture value calculation circuit 46.

is smaller than the open aperture value of the aperture blades 52, even if the aperture is opened, the exposure becomes amplified. On the other hand, the appropriate aperture value F
If No is larger than the minimum aperture value of the aperture blades 52,
Even if you close the aperture to the minimum, the image will be overexposed. Therefore,
Since the aperture value calculation circuit 46 cannot control when the obtained aperture value FNo is outside the range of "open aperture value" to "minimum aperture value", a lamp, buzzer, etc. A warning is issued, the operation of the aperture control GA mechanism 50 is prohibited, or the release is locked. This makes it possible to prevent photographing without proper exposure.

Among the component blocks in FIG. 4, the aperture control mechanism 50,
The components other than the aperture value encoder 54 may be provided on the S)0 side or on the camera side. That is,
The strobe can be a standalone flash or one built into the camera. However, when the strobe is provided at a position away from the camera body, the distance measuring sections 40, 42 and the reflectance measuring section 44 need to be provided on the strobe side.

According to the first embodiment, the distance between the strobe and the subject, the distance between the strobe and the reflective object, and the reflectance of the reflective object are determined using the PSD, so that indirect irradiation can be achieved with a simple configuration. In addition to determining the appropriate aperture value according to the actual optical path length from the strobe to the subject,
If the aperture value is outside the controllable aperture range, exposure control failure can be prevented by issuing a warning or prohibiting the photographing operation.

Next, a second embodiment will be explained. In the first embodiment, assuming that the distance between the strobe 10 and the reflective object 14 and the distance between the subject 12 and the reflective object 14 are both Lb, the strobe 10 and the virtual subject 12a are calculated from equation (2) or equation (2a). The distance (actual optical path length) Lc was calculated, but the strobe 10
In some cases, the object 12 and the object 12 are not equidistant from the reflecting object 14, and the second embodiment is an example for such a case.

First, as shown in Fig. 5, a strobe 1o and a reflective object 1 are
4 is the distance L between the subject 12 and the reflective object 14.
A case where it is shorter than d/2 will be explained.

In this case, the distance i between the strobe 10 and the virtual subject 12a
! fILc can be obtained as follows.

L c −L f /cosγ...
(17)Lf−Laxcosδ−(18)7
=jan-1((2L b + La X5lnδ
)/Lf+ (19) Here, δ is the photographing angle of the camera with respect to the horizontal direction, and if the reflecting object is a ceiling, it can be detected by detecting the angle of the camera with respect to the direction of gravity.

Substituting equations (18) and (19) into equation (17), Lc
can be expressed by the known La, Lb, and δ as follows.

L c −L a X cos δ÷ co
s[tan' f(2L b + L
a X sin δ )/(LaX cos δ
)11 - (20) (20) formula, (1) formula, (
From equation 4), the appropriate aperture value can be determined as follows.

F No −G N n /L c= v'T':
x G N O÷(L a X aos δ)X c
os[jan ” f(2L b + L a X s
in δ)/(LaXcosδ)+1 −(21)(
If δ-0 is used in equation 21), equation (5) is obtained.

Similarly, in the case of Lb>Ld/2 as shown in Fig. 6,
Lc can be determined as follows.

L c −L a X cos δ÷cos
[tan' ((2L b -L a X si
nδ)/(LaXcos δ)) co-(
22) From equations (22), (1), and (4), the optimal aperture value is determined as follows.

F No -G N n / L c-
5x G N o + (L a x cos δ
)X'cos[tan' ((2L b -L
a X sin δ)/(LaX cos δ)+1
-(23) If δ−〇 is used in equation (23), equation (6) is obtained.

Equation (23) differs from Equation (2) only in the sign of the term related to δ, and the rest is the same. Therefore, in the case of Figure 5, δ
is positive and δ is negative in the case of Fig. 6, the appropriate aperture value FN
o can be expressed by the same equation (21).

Therefore, the second embodiment is realized by adding a sensor for detecting the angle of the camera with respect to the direction of gravity to the configuration shown in FIG. 4, and changing the calculation formula of the aperture value calculation circuit 46 to formula (21). can.

In this way, according to the second embodiment, even if the strobe 10 and the subject 12 are not equidistant from the reflective object 14,
Accurate exposure control is possible.

Note that this invention is not limited to the embodiments described above, and can be modified in various ways. For example, the distance measuring element and reflectance measuring element are not limited to PSD. Exposure control is not limited to using an aperture, but may also be performed using a strobe light emission time. Also, it is not necessary to issue both a warning and a prohibition on photography.
Only one of them may be used, and the types of warnings are not limited to those described above.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a simple (14-component) exposure control device that can always properly control exposure during indirect illumination photography using a bounce strobe, regardless of the reflectance of the subject. can.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of indirect strobe irradiation, Figure 2 is the distance,
FIG. 3 is a diagram showing the principle of determining the distance 71ξ; FIG. 4 is a block diagram showing the configuration of the first embodiment of the present invention; Fifth
6 are conceptual diagrams of indirect irradiation in the second embodiment. 10... Strobe, 12... Subject, 12a...
Virtual subject, 14... reflective object. Applicant's agent Patent attorney Atsushi Tsuboi Figure 2h---10---M

Claims (1)

[Claims] An exposure control device that determines the exposure when illuminating the object after reflecting light from a strobe on the object, comprising: means for measuring a distance between the strobe and the object; and a means for measuring the distance between the strobe and the object. means for measuring the reflectance of the object; and determining an appropriate exposure value according to the distance to the subject, the distance to the object, and the reflectance of the object, and the appropriate exposure value is outside the controllable exposure range of the camera. In this case, an exposure control device equipped with a means to issue a warning or prohibit photography.