JPH04119336A - Photometric device of camera - Google Patents

Abstract

PURPOSE:To eliminate the inconvenience that a user makes photographing without noticing that an exact metered value is not obtd. by discriminating the subject light having a strong deviation of polarizing components and making alarm and correction of the metered value at need. CONSTITUTION:The output of a 1st photometric means 11 which makes photometry by using the light reflected from a dielectric half mirror 3 and the output of a 2nd photometric means 13 which makes photometry by using the light transmitted through the dielectric half mirror 3 are compared 14 and the polarization state of the subject light is decided. The light is judged to be the subject light having the strong deviation of the polarizing components when the difference between the two outputs is large. The alarm or the correction of the metered value is then executed at need. Such inconvenience that the user makes photographing without noticing that the exact metered value is not obtd. is eliminated in this way.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a dielectric half mirror that separates a light beam transmitted through a photographing lens into a light beam to a finder and a light beam for photometry.
The present invention relates to a photometric device for a camera equipped with a camera.

[Prior Art] Conventionally, this type of photometric device has been disclosed, for example, in Japanese Patent Application Laid-Open No. 63-708.
As disclosed in Publication No. 35, subject light that has passed through a photographic lens, etc. is directed to a finder (in most cases, a first photometer is arranged) using a half mirror made of a dielectric multilayer film. A photometry device for a single-lens reflex camera that separates a light beam into a light beam and a light beam for a second photometer is known.

[Problems to be Solved by the Invention] However, in a photometric device configured in this way, the half mirror configured with a dielectric multilayer film has a P-polarized light component vibrating within the plane of incidence and a plane perpendicular to the plane of incidence. Generally, the reflectance (or transmittance) is different from that of the oscillating S-polarized light component.

Therefore, in the case of subject light with a strong polarization component, such as reflected light from water surfaces or glass, the intensity ratio of reflected light and transmitted light changes, and accurate photometric values cannot be obtained with either the first or second photometric means. I can't get it.

Moreover, there is a problem in that there is no means to warn of such a situation and no means to correct the photometric value.

The present invention has been made in view of such conventional problems, and is capable of determining the above-mentioned situations and issuing warnings and warnings as necessary.
It is an object of the present invention to provide a photometric device for a camera that makes it possible to correct photometric values.

[Means for Solving the Problems] In order to solve these problems, the camera photometry device according to the present invention separates the subject light transmitted through the photographing lens into a light beam for viewfinder photometry and a light beam for body photometry. In a camera equipped with a dielectric half mirror, a first photometry means for measuring the light flux for viewfinder photometry, a second photometry means for measuring the light flux for body photometry, and an output of the first photometry means. and a comparison calculation means for comparing the output of the second photometry means and the output of the second photometry means to determine the polarization state of the subject light.

Further, in the photometering device of another camera according to the present invention, when the ratio between the output of the first photometer and the output of the second photometer deviates from a predetermined ratio, a warning means is activated or a comparison is made. A correction means is provided for correcting the photometric value calculated by the calculation means.

Further, in another camera photometry device according to the present invention, in the photometry device described above, the second photometry means also serves as focus detection means.

[Function] In the present invention, as described above, the output of the first photometric means that measures light using the reflected light of the dielectric half mirror, and the second photometric means that measures light using the transmitted light of the dielectric half mirror. The polarization state of the subject light is determined.

If the difference between the two outputs is large, it is determined that the subject light has a strong bias in polarization components, and by issuing a warning or correcting the photometric value as necessary, it is possible to detect the problem even though the accurate photometric value is not obtained as described above. This eliminates the inconvenience of having to take a picture without using it.

[Embodiment] FIG. 1 is a longitudinal cross-sectional view of a single-lens reflex camera showing the configuration of an embodiment of a photometric device for a camera according to the present invention. Note that the embodiment is not limited to this example.

As shown in FIG. 1, the single-lens reflex camera according to the present invention includes a quick return mirror 3 whose part or entire surface is a dielectric multilayer half mirror, which is disposed between a photographing lens 1 and a shutter 2. Most of the subject light transmitted through the photographing lens 1 is reflected by the quick return mirror 3, and is reflected by the focusing screen 4. The light is observed as a finder image through the pentaprism 5 and the eyepiece 6, and is distributed to the first photometry means 11 through the first condenser lens 10.

On the other hand, a part of the subject light that has passed through the photographic lens 1 passes through the quick return mirror 3, is reflected by the sub-mirror 7, passes through the second condensing lens 12 disposed at the bottom of the camera body, and is sent to the second photometer 13. guided by.

Photometric output of first photometric means 11 and second photometric means 1
The photometric output of No. 3 is input to the comparison calculation means 14.

FIG. 2(a) shows the photometry area of the first photometry means in the screen area on the screen 4. FIG. The first photometry means is a divided photometry means that measures light for each area A to F as shown in FIG. ~ Output SIF.

Similarly, FIG. 2(b) shows the photometry area of the second photometry means in the screen area. The second photometric means is
As shown in FIG. 2(b), it is a spot photometer that measures the central spot area G, and outputs a photometric value S2 proportional to the image plane illuminance of the screen area G.

The first and second photometric means each have a quick return output ratio between the photometric values SIA to SIF (hereinafter referred to as Sl unless otherwise specified) and the photometric value S2 on a uniform brightness plane with no polarization component bias. Average reflectance Ra of mirror 3
(e.g. 0°7) and average transmittance (e.g. Tag, 3)
The gain is adjusted so that the output ratio is the same (for example, 7:3).

Normally, with a photometer that uses a light beam transmitted through a quick return mirror, it is difficult to arrange a photometer that measures the entire screen due to restrictions on the size of the submirror.

Region A in FIG. 2(a) and region G in FIG. 2(b) are approximately the same region.

FIG. 3 schematically shows an example of the reflectance and transmittance of a dielectric multilayer film half mirror.

In the case of a dielectric multilayer half mirror, the loss of light amount due to absorption can be ignored, so the average transmittance is Ta003. For the average reflectance Ra=0.7, the transmittance 'rp of the P-polarized light component vibrating within the plane of incidence is 0.45, and the reflectance Rp is 0.55. The transmittance Ts of the S-polarized light component vibrating in a plane perpendicular to the plane of incidence is 0.
．． 15. The reflectance Rs is 0.85.

To explain this in conjunction with the embodiment shown in FIG. 1, when the component of the object light that has passed through the photographic lens 1 that oscillates within the plane of paper is the V component, the ■ component is the component that vibrates within the plane of incidence with respect to the quick return mirror 3. This corresponds to the oscillating P-polarized light component.

Similarly, when the component of the subject light transmitted through the photographic lens 1 that vibrates in a plane perpendicular to the plane of the drawing is the H component, the H component corresponds to the S polarization component of the quick return mirror 3.

Usually, as shown in area A in FIG. 2(a) and area G in FIG. If both second photometering means measure light in substantially the same area, they will output substantially the same photometric value in the normal case where there is no bias in the polarization component, and will output an accurate value as the photometric value of the subject light.

However, if the reflected light from the water surface or the reflected light from a show window is the subject light under backlit conditions, the polarization components are largely biased, and the intensity ratio between the reflected light and the transmitted light from the quick return mirror 3 changes.

To explain specifically, the V component in this subject light is called V
If the A and H components are HA, then according to the example of the dielectric multilayer film half mirror described above, the V component Vl and the H component H in the reflected light of the quick return mirror 3 guided to the first photometric means.
1 is as follows.

V1=0.55XVA H1=0.85X
Similarly to HA, the V component V2. in the light transmitted through the quick return mirror 3 guided to the second photometric means. The H component H2 is as follows.

V2=0.45XVA H2=O, 15XHA The intensities of the above reflected light and transmitted light are (V1+81)/2, respectively.
(It can be expressed as V2+H2>/2.

If this subject light has no polarization component bias and the ■ component and H component are the same (HA=VA), the reflected light from the quick return mirror 3 guided to the first photometric means and the reflected light guided to the second photometric means. The intensity ratio between the transmitted light and the transmitted light of the quick return mirror 3 is as follows.

(0,55+0.85)/2: (0,45+0.15
)/22.33:1 ・ ・ ・ (1) Here, if there is a bias in the polarization component of the subject light and the H component is four times as strong as the V component (HA' = 4XVA"), this reflection The intensity ratio between the light and the transmitted light is as follows.

(0,55+0.85 x 4)/2: (0,45+
0.15 x 4)/23.76:1 ・ ・ ・ (2) When there is a bias in the polarization component of the subject light, as in the latter case above, each photometry means not only outputs different photometry values; As described above, since the intensity ratio between the reflected light and the transmitted light of the tight return mirror 3 changes, each photometric value output alone is not accurate as a photometric value of the subject light.

Therefore, the comparison calculation means 14 compares the photometric output SIA of the area A of the first photometric means and the photometric output S2 of the second photometric means based on the above.

The algorithm of the comparison calculation means 14 is shown in FIG. 4 below.

First, the photometric output s1 is input from Stella 7jlO (hereinafter abbreviated as jlO) at jll as a star.

Next, the photometric output S2 is inputted at j12.

Next, in j13, the ratio between the photometric output SIA and the photometric output S2 is determined.

C1<1(S2/5IA)X (Ra/Ta)l<C2
0<C1<1, 1<C2: Constant Ra: Average reflectance of the quick return mirror Ta: Average transmission of the quick return mirror When the ratio of the two outputs exceeds a predetermined level and the above formula is not satisfied, As explained above, it is assumed that the polarization component of the subject light is biased, and the process proceeds to j14, where a warning means (not shown) warns the photographer that Sl or S2 is inaccurate.

If the above formula is satisfied, proceed directly to j15,
A normal photometric calculation is performed from the obtained photometric output, and the operation ends at j16.

As an application example of the above algorithm, when the difference in re-output exceeds a predetermined level and the above formula is not satisfied, it is possible to treat the situation as photographing under backlight conditions and activate a countermeasure.

As a countermeasure, for example, a predetermined backlight correction coefficient (for example, a coefficient that quadruples the exposure amount) can be added to the photometric value calculated from Sl or S2 to correct overexposure.

Alternatively, it is also possible to assume that the photograph is taken under backlight conditions and emit light from a built-in strobe or an external strobe (not shown) to illuminate the main subject, thereby preventing the main subject from being immersed in darkness.

Alternatively, if the photographer intentionally wishes to shoot under conditions where the polarized light components are biased, or if he or she is wearing a linear polarizing filter, the photographer may operate the camera or attach a prescribed linear polarizing filter. This activates countermeasure prohibition means (not shown), and prohibits the above-mentioned warning means and countermeasures, such as adding a backlight correction coefficient and flashing a strobe.

Alternatively, the comparison calculation means 14 determines the brightness condition indicating backlight photography, and if some areas of the subject on the screen have extremely high brightness (for example, 10,000 Cd/m2 or more), or the light metering between each area of the screen is determined. The output ratio is large (e.g. 6
If the backlight brightness conditions such as (2 times or more) are not met, the above warning means and countermeasures are prohibited from operating.

Note that the brightness conditions that prohibit the operation of the above countermeasures are not uniform, but vary depending on the photographer's settings and the lens.

May be changed depending on accessory attachment conditions An example of the above application is shown in FIG.

First, the operation of the comparison calculation means 14 is started at j20,
Input the photometric output Sl at j21, and input the photometric output S2 at j22.
Enter.

Next, in j23, the ratio of the photometric output SIA and the photometric output S2 is set to the fourth value.
Judgment is made as shown in the example in the figure.

If the re-output ratio is within a predetermined level, the process proceeds to j28.

If the re-output ratio exceeds a predetermined level, the process proceeds to j24, where it is determined whether the countermeasure inhibiting means has issued a signal to inhibit operation.

If an operation prohibition signal is detected at j24, j? Proceed to step 8.

If the operation prohibition signal is not detected in j24, the process proceeds to j25 to determine the brightness condition, and if the backlight brightness condition is not satisfied, the process similarly proceeds to j28.

If the backlight brightness condition is satisfied at j25, proceed to j26,
The warning means is activated in the same manner as in the example shown in FIG.

Next, the process proceeds to j27, where countermeasures such as adding a backlight correction coefficient and flashing a strobe are activated, and the process proceeds to j28.

j28 performs normal photometric calculations from the photometric output that would not be obtained when the countermeasure means is not operating, and when the countermeasure means is operating, performs photometric calculations taking into account the backlight correction coefficient added from the countermeasure means. , the operation ends at j29.

FIG. 6 is a longitudinal sectional view of a single-lens reflex camera showing another embodiment of the present invention, and the same parts as in the above-mentioned figures are given the same reference numerals. In the figure, a switch 15 is provided on the outside of the camera body as a countermeasure inhibiting means for outputting an operation inhibiting signal to the comparison calculation means 14 mentioned above.

In addition, the photometric output S1 and the photometric output S2 as described above
When the gain is adjusted, the photometric output SIA of area A of the first photometric means and the photometric output S2 of the second photometric means are
If the photometric calculation is performed by always adding the two photometric values, the total output of both photometric values will be constant regardless of the polarization condition of the subject light, so that accurate photometric calculation can always be performed.

To explain the above photometric calculation, under the subject light conditions shown in equation (1) above, the intensity ratio (2,33:l) of the reflected light and transmitted light of the quick return mirror 3, the photometric output SIA, and the photometric output S2. From the output ratio condition (7:3), the photometric output SI
When the convenient gain constant (constant including both optical and electrical) for obtaining A is GIA, and the gain constant for obtaining photometric output S2 is 02, the following equation is obtained.

(2,33/3.33)XGIA=SIA (]/
3.33)xc2=52(2,33/3.33)xc
lA=7 (1/3.33) x G2=3
CIA 210 G2=10... (
3) Also, the following formula is obtained.

SIA+32=10 On the other hand, CIA obtained by equation (3) under the conditions of equation (2),
When SIA' and 32' are calculated using G2, the following formula is obtained.

(3,76/4.76)XGIA=S]A'(3,76
/4.76)X 10=SIA'SIA'=7.9 (1/4.76)X G2=S2" (]/4.76)X 10=32'82'=2.1 5) Therefore, the following formula is obtained.

SIA'+32'=10 ・ ・ -(6> Although the ratio of polarized light components is different, the amount of subject light is the same under the above two conditions, so from equations (4) and (6), both photometry It can be seen that the total output of the values is constant regardless of the polarization condition of the subject light.

FIG. 7 shows the above example. After starting the operation of the comparison calculation means 14 at j30 and executing the series of algorithms shown in FIG. 4, at j34 the photometry mode is set by the photometry mode setting means (not shown). Determine whether spot metering is set.

If it is determined in j34 that the spot photometry mode is not set, the process proceeds to j35, executes a series of algorithms shown in FIG. 4, and then ends in j37.

If it is determined in j34 that the spot photometry mode is set, the process proceeds to j38, where the value of the photometry output SIA and the value of the photometry output S2 are added.

Next, at j39, a photometric calculation is performed based on the total output, and the process proceeds to j37 to end the operation.

Furthermore, the second photometric means described above can be replaced with a known focus detection means.

The photometric output S2 of the second photometric means can be calculated from the output of the focus detection means, which has the advantage of avoiding an increase in cost due to duplication of photometric means. In that case, Fig. 8(a),
As shown in (b), it is preferable to match the shape of the photometry area A of the first photometry means to the shape of the area G of the focus detection means, which is the second photometry means. In addition, the area A shown in FIGS. 8(a) and (b)
, G may use a line-shaped CCD.

[Effects of the Invention] As explained above, in the present invention, it is possible to determine that the subject light has a strong polarization component, and issue a warning and correct the photometric value as necessary, so that accurate photometric values can be obtained. Extremely excellent effects can be obtained, such as eliminating the inconvenience of unknowingly taking a picture without being able to obtain it.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a single-lens reflex camera according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) are the photometric area of the first photometric means and the second photometric area of the photographic screen, respectively. FIG. 3 is a diagram showing the transmittance and reflectance of the dielectric multilayer film half mirror. FIG. 4 is a diagram showing an example of the operation of the comparison calculation means. FIG. 5 is a diagram showing another example of the comparison calculation means. 6 is a longitudinal sectional view of a single-lens reflex camera according to another embodiment of the present invention, FIG. 7 is a diagram showing an example of the operation of the comparison calculation means during spot photometry operation, and FIG. 8 ( a) and (b) are the photometry area of the first photometry means and the second photometry area on the photographic screen, respectively.
FIG. 4 is a diagram showing another example of the photometric area of the photometric means of FIG. 1... Imaging lens, 3... Quick return mirror, 4... Focusing screen, 7...
- Sub-mirror, 11... First photometry means, 13...
・-Second photometric means, 14... Comparison calculation means, 15
····switch. Figure (α) (b) No.? Figure ○yo DJ 20 11 ■ J2 0-guchi J22 1J28 Figure 5 Figure 6 Figure C ■ F 0 ``Flo J3 0 Go ■ J32 Not (α U Figure 8

Claims (3)

[Claims] (1) In a camera equipped with a dielectric half mirror that separates the subject light transmitted through the photographic lens into a light flux for finder photometry and a light flux for body photometry, a first photometry means for measuring the light flux for finder photometry. and a second photometric means for metering the light flux for body photometry; and a comparison for determining the polarization state of the subject light by comparing the output of the first photometric means and the output of the second photometric means. A photometric device for a camera, comprising: a calculation means; (2) In claim 1, when the ratio between the output of the first photometric means and the output of the second photometric means deviates from a predetermined ratio, the photometric value calculated by the warning means or the comparison calculation means is A photometry device for a camera, characterized in that it is provided with a correction means for applying correction. (3) The photometry device for a camera according to claim 1, wherein the second photometry means also serves as focus detection means.