JPS6042900B2 - Photometric device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photometric device, and particularly to a photometric device that can obtain a desired photometric distribution.

2. Description of the Related Art Apparatuses that perform photometry by condensing light from a photometric object such as an object or information onto a photometric element using a condensing optical system such as a lens are already known.

In such devices, due to vignetting and the COS' law, the photometric weight at the periphery of the photometric field tends to be significantly lower than that at the center, that is, there is a tendency for center-weighted photometry.

This photometric device is not preferred when photometry is desired in which the photometric weight at the periphery of the photometric field is not significantly lower than that at the center. In particular, in photometering devices for cine cameras that photograph continuous scenes, center-weighted photometry is not preferred, and average photometry is desired, since panning operations involve sudden changes in the exposure of the screen. Therefore, in a photometric device that uses a condensing optical system,
L', -1-|[■ It is desirable to change the old 6 to -■1Hh cloth [IX-Yo small photometric distribution.

The present invention has been made in consideration of this point.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a photometric device using a condensing optical system with a modified photometric distribution. and,
This objective is achieved by forming the photometric distribution changing means as a part of the condensing optical system. That is, the present invention is characterized in that the photometric distribution changing means is not simply provided within the apparatus, but is formed as a part of the condensing optical system.

Due to this feature, it not only changes the photometric distribution but also has effects such as ease of manufacturing. Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an optical arrangement diagram of a cine camera having a conventional photometric device, in which numeral 1 denotes an objective lens which forms an object image on a film 3. As shown in FIG. Reference numeral 1' denotes a beam splitter disposed in the objective lens 1, which splits light in the direction of a finder optical system (not shown).

2) is a light splitter for photometric light beam splitting arranged between the objective lens 1 and the film 3; This light splitter 2 has a half mirror tilted with respect to the optical axis between parallel plane plates.
The light reflected by this half mirror is totally reflected by the incident surface of the light splitter and exits from the incident surface. 4
is a lens.

The objective lens 1 and this lens 4 constitute a condensing optical system for the photometric element 5. The photometric element 5 is arranged near the exit pupil position of the condensing optical system. Further, the lens 4 may be a concave mirror depending on the arrangement position of the photometric element 5, etc. FIG. 2 shows a portion of the photometric element 5 in FIG. 1.

As can be seen from this figure, the beam width of the off-axis light 10 is narrower than that of the on-axis light 11 due to the relative radial eclipse. Furthermore, CO
The peripheral illuminance decreases due to reasons such as a decrease in illuminance due to the S4 rule, a loss in the amount of light at the saw section when the lens 4 is a Fresnel lens, or a portion of off-axis light not entering the photometric element. For this reason, a photometric device using a conventional condensing optical system has a center-weighted photometric distribution. For this reason,
The photometric device of the present invention has a means for changing the photometric distribution in the condensing optical system, particularly in the lens disposed between the objective lens 1 and the photometric element 5. The distribution has changed. FIG. 3 shows a lens 13 applied to the photometric device of the present invention.

This lens 13 is placed in place of lens 4 in FIG. A diffusing surface 6 is formed on the optical axis of this lens as a means for changing the photometric distribution. This diffusion surface is formed by a matte surface such as ground glass, a diffraction grating surface, etc.
However, it is desirable that at least this portion has a diffusion characteristic in which the light incident on this portion is diffused more than on the photometric element surface.
With this configuration, a certain portion of the light passing through the center of the lens 13 is diffused and does not enter the photometric element 5, so that the photometric distribution changes ζ. Therefore, average photometry can be performed by appropriately setting the degree of diffusion, the size of the diffusion surface, etc. FIG. 5B shows the photometric distribution obtained by the lens 13 of FIG.

It will be appreciated that the photometric weights are averaged over different parts of the screen as compared to the center-weighted photometric distribution obtained with the apparatus of FIG. 1 shown in FIG. 5A. FIG. 4 shows a lens 15 used in a second embodiment of the invention.

This lens 15 is formed with means for changing the normal light focusing action of the light focusing optical system as a means for changing the photometric distribution, such as a surface with a different curvature, a notch in the lens, a light shielding plate, etc. In the embodiment shown in FIG. 4, a Fresnel-free surface 8 is formed. Further, this Fresnel non-forming surface 8 is formed at a position that does not direct light from the upper part of the field, that is, the sky, toward the photometric element 5. That is, since the Fresnel non-forming surface 8 is a transparent surface, by arranging the photometric element 5 away from the passing position of the transparent light beam, much of the light in this portion is not photometered. Therefore, the photometric distribution is changed. The reason why photometry is not performed in the sky is to obtain appropriate exposure without being affected by light from the bright sky. Of course, the same effect can be obtained by placing a light shielding plate on the 8 portions of the Fresnel forming surface. Although it is possible to change the photometric distribution using this Fresnel-free surface 8, in this embodiment, in order to further obtain a desired photometric distribution, a diffusing surface 6 is provided at the center as shown in FIG. It is being As a result, the photometric weight of the empty area is low, and a photometric distribution of average photometry is obtained in other areas. This photometric distribution is shown in FIG. 5C. Note that 16 in FIG. 4 is a lens holder. Furthermore, in both the embodiments shown in FIGS. 3 and 4, it is preferable for the Fresnel surface 7 to be placed on the light splitter 2 side in view of the diffusion effect.

[Brief explanation of drawings]

1 and 2 are optical layout diagrams of a cine camera to which a conventional photometric device using a condensing optical system is applied, and FIG. 3 shows a condensing optical system applied to the first embodiment of the photometric device of the present invention. FIG. 4 is a diagram showing a condensing optical system applied to the second embodiment,
FIG. 5 is a diagram showing the photometric distribution. In the figure, 1 and 4 are condensing optical systems, 2 is a light splitter, 3 is a film, 5 is a photometric element, 6 is a diffusing surface, 7 is a Fresnel surface, 8 is a Fresnel-free surface, 10 is off-axis light, 11 is on-axis light, 13
, 15 are Fresnel lenses.

Claims (1)

[Claims] 1. In a photometry device that performs photometry by condensing light from a photometric object onto a photometric element using a condensing optical system, a diffusion device that diffuses a luminous flux near the optical axis of the condensing optical system in a part of the condensing optical system. 1. A photometric device characterized in that an optical member having a means is arranged to change the photometric distribution of a photometric object.