JPH0210335A - Finder optical system with photometry means - Google Patents

Abstract

PURPOSE:To secure a light measurement area with the same rate with a photographic field and to obtain excellent light measurement information by providing a means which divides luminous flux passed through an objective system into two pieces of luminous flux and guides one piece of luminous flux to a light measurement part in the light measurement system. CONSTITUTION:The luminous flux from a subject forms a finder image on an image formation plane 4 through the objective system 1a which is varied in power associatively with the focal length of an image pickup lens system. Then the luminous flux is divided into the pieces of luminous flux for finder image observation and light measurement by an optical dividing means 10 which is arranged at 45 deg. to the finder optical axis in a secondary image forming lens system 2a. The divided piece of luminous flux for finder image observation is image-formed again on an image formation plate 7 through the secondary image forming lens system 2a and observed through an ocular 8. Then the luminous flux for light measurement is deflected to the light measurement part 3a, image-formed on a light measuring element 12 through a condenser lens for light measurement, and processed to obtain a light measured value. Thus, the light measurement area with the same rate with the photographic field is secured and the excellent light measurement information is obtained.

Description

Detailed Description of the Invention (Field of Application on A8x) The present invention relates to a finder optical system having a photometric means,
In particular, by using the variable magnification means provided in a part of the objective lens of the external finder optical system, which is linked to the change in the angle of view of the photographing lens with variable magnification function, the photometry area can be arbitrarily changed to perform photometry. The present invention relates to a finder optical system having a photometric means that enables exposure control of viscosity.

(Conventional Technique 4I) Recently, so-called electronic still cameras have been widely used as consumer video information equipment. This electronic camera uses an electrical element such as a solid-state image sensor as a photoreceptor.

The dynamic range of solid-state image sensors is generally narrow (the latitude width of Am is extremely narrow when compared with cameras using conventional silver halide photoreceptors).

For this reason, in electronic cameras using solid-state Ti image elements, exposure control must be performed accurately, and the electrical system or mechanism inside the camera tends to become complicated.

Generally, closed-loop control based on photometric information is considered optimal for electronic still cameras due to reasons such as shutter time lag.

On the other hand, in recent years, in order to expand the photographic area, even non-TTL type cameras are equipped with photographic lenses having variable magnification functions. In a camera using this photographic lens, it is necessary to obtain accurate photometric information, and it has become necessary, for example, to change the photometric range in conjunction with changes in the Il image field.

For example, in a conventional outer al side light means, if the optimum photometry range is set at the middle value of the focal length range of the photographing lens, on the short focal length side the ratio of the photometry area to the photographing field becomes small, so-called. Spot photometry is used, and conversely, since the ratio of the photometry area increases on the long focal length side, so-called average photometry is used. As described above, in the past, it was difficult to obtain an appropriate photometric range because the ratio of the photometric area to the photographic field changed as the focal length of the photographic lens changed.

Conventionally, as a means to solve the above problem, (a) tM
The angle of view of the photometric lens that makes up the photometric optical system is mechanically changed in conjunction with the change in the focal length of the shadow lens.

(b) The photometric element itself is divided into multiple parts and used in conjunction with changes in the focal length of the photographic lens.

The answer is known.

Specific means for the above (a) include a method of providing a magnification changer in the photometric lens system itself, a method of displacing the relative position of the photometric lens system and the photometric element, and a method of installing a sub-diaphragm in front of the side light element. There are ways to put it in and take it out.

However, in all of these methods, the interior of the camera becomes mechanically complex, making it very difficult to miniaturize the camera.

The means (b) above is a means conventionally used to switch the photometric sensitivity distribution according to the brightness pattern of the subject. However, a means for electrically detecting the focal length of the photographic lens is required, which complicates the entire apparatus, and there are also problems in that stepless and continuous changes cannot be made.

(Problems to be Solved by the Invention) The present invention provides a variable magnification means in the objective lens system that constitutes the finder optical system, and guides a part of the light flux that has passed through the objective lens system to the photometry section by the light guide means. A finder optical system that has a photometering means with a simple configuration that allows for high-precision exposure control over the entire magnification range by always obtaining the same proportion of the photometry area for the shooting field of the photographic lens. The purpose is to provide.

(Means for solving the problem) Il! the finder real image formed by a dedicated objective lens system with the eyepiece lens! The objective lens system has a variable magnification means, the light beam passing through the objective lens system is divided into at least two light beams by a light splitting means, and one of the divided light beams is divided into two light beams. The light was guided to a photometry section via a light guide means and used as a light beam for photometry.

(Embodiment) FIG. 1 is a schematic diagram of an optical system of an embodiment in which the present invention is applied to a secondary imaging type finder optical system.

In the figure, reference numeral 1 denotes a secondary imaging type finder optical system, which is provided separately from a photographic lens system having a variable magnification system (not shown). An objective lens system la has a variable magnification means and is composed of two lenses, a negative lens 2 and a positive lens 3. Moreover, the two lenses 2 and 3 constituting the objective lens system 1a change their relative positions i! according to changes in the focal length of a photographing lens system (not shown). The observation field is changed with respect to the shooting field by 1S and displacement.

Reference numeral 4 denotes a primary imaging plane, on which a finder image is formed by the objective lens system 1a. A secondary imaging lens system 2a is composed of two secondary lenses 5 and 6. 7
is the secondary imaging plane, and the first imaging plane by the secondary imaging lens system 2a is
The finder image on the next imaging plane is re-imaged. 8 is the contact lens, 9 is the viewfinder image @H, t
.

is a light splitting means and has a semi-transparent part, and is arranged between two secondary lenses 5.6 of the secondary imaging lens system 2a on the finder optical axis at an angle of 45 degrees with respect to the finder optical axis. has been done. The light beam passing through the objective lens la is divided into a light beam for viewfinder image observation and a light beam for photometry.

Reference numeral 11 denotes a light guiding means, which is composed of a condensing lens. 3a
1 is a photometry section, which is a device composed of a photometry element 12.Next, the imaging state of the finder image of the finder optical system having the photometry means in this embodiment and the photometry method will be explained.

The light flux from the subject is formed into a first image by an objective lens system 1a whose magnification is changed in conjunction with changes in the focal length of a photographic lens system (not shown), and then a finder image is formed on the first image. After the light flux from the secondary imaging surface 4 enters the secondary lens 5, it is
The light beam is divided into a light beam for viewfinder image observation and a light beam for photometry by a light splitting means 10 arranged at an angle of 5 degrees.

Finder image Ill divided by light splitting means IO
The light beam for detection is re-imaged on the secondary imaging surface 7 by the secondary imaging lens system 2a. The finder image formed on the 0'S secondary imaging plane at this time is observed through the eyepiece lens 8.

On the other hand, the light beam for photometry is deflected to the photometry section 3a above the camera, is focused on the photometry element lz via the photometry condensing lens 11, and is processed by an arithmetic operation ytl (not shown) to obtain the photometry f.
I got 1.

In this embodiment, the angular field photometered by the photometer 3a corresponds to the photographing field 1, since the light beam passing through the objective lens is used to control the variable magnification system linked to the photographing lens. This ensures that the ratio of the photometric area to one field of photography is always constant.

In addition, since the objective lens system 1a that makes up the finder optical system also serves as a photometric lens system, no additional parts are required and the number of apertures laid out on the front of the camera is the same as that of conventional cameras. It takes up less space than the previous model, making it more space efficient.

1. In this embodiment, the light splitting means 10 is disposed within the secondary imaging lens system 2a, but the objective lens system 1 having a variable magnification means is
It may be located anywhere as long as it is behind a.

In addition, a desired photometric sensitivity distribution can be easily obtained by the area and reflectance distribution of the semi-transmissive part of the light splitting means 10, and the semi-transparent part can be observed by the observer through the eyepiece 8, and the photometric range can be determined. You can also check it on the finder.

FIG. 2 is a perspective view of another embodiment in which the present invention is applied to a primary imaging type finder optical system using a Porro prism.

In the figure, 21a is an objective lens system having a variable magnification means, and is composed of two lenses 21 and 22. 23
is a Porro prism for an erect image, and the Porro prism 23
A semi-transmissive portion is provided on the first reflecting surface 26 of the prism to divide the light beam incident on the prism into a light beam for viewfinder image observation and a light beam for photometry.

Reference numeral 27 denotes a light guiding prism, which is fixed to the first reflecting surface 26 of the Porro prism 23. 28 is a condensing lens for photometry,
Reference numeral 29a denotes a photometric section, which is composed of a photometric element 29.

24 is an access lens, and 25 is an observation pupil for observing a finder image.

In this embodiment, the luminous flux from the subject changes i! due to changes in the focal length of the photographic lens system having a magnification variable means (not shown). 11! F
After passing through the objective lens system 21a, which is displaced by jI, the light enters the Porro prism 23.

The light beam is divided into a light beam for observing the finder image and a light beam for photometry by a light splitting p-stage consisting of a semi-transparent section provided on the first reflecting surface 26 of the Porro prism 23. The divided light flux for viewfinder image observation is reflected within the Porro prism and then passes through the eyepiece lens 24 to the observation pupil 25.
The light is guided through the lens, and the viewfinder image is observed using this light.

On the other hand, the light beam for photometry passes through a light guiding prism 27 fixed to the t51 reflecting surface 26 of the Porro prism 23, and is focused on the surface of the photometric element 29 by a light guiding means 28 consisting of a condensing lens. At this time, the output signal from the photometry section 29a is calculated by a calculation device to perform photometry.

In this embodiment, similarly to the embodiment shown in FIG. Highly accurate photometry is possible by keeping the ratio of the photometry area constant for each shooting field.

(Effects of the Invention) According to the present invention, the objective lens system constituting the finder optical system is provided with a variable magnification means, and the light beam passing through the objective lens system is divided into two light beams by the light splitting means, and one of the light beams is divided into two light beams. A light guiding means for guiding light to the photometric section is provided in the photometric system.

As a result, regardless of changes in the focal length of the photographing lens, that is, regardless of magnification changes, it is possible to always secure a photometry area of the same proportion to the photographic angle field.1 For example, good photometry can be achieved even in cameras using solid-state image sensors with strict exposure accuracy. It is possible to achieve a finder optical system having a photometric means with a simple configuration that allows information to be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an optical system of an embodiment in which the present invention is applied to a secondary imaging type finder optical system, and Fig. 2 is a schematic diagram of an optical system in which the present invention is applied to a primary imaging type finder optical system using a Porro prism. FIG. 7 is a perspective view of another embodiment when applied to an optical system. In the figure, la and 21a are objective lens systems, 2,321.22
is a lens, 4 is a primary imaging surface, 5 and 6 are secondary lenses, 7
is a secondary imaging plane, 8.24 is an eyepiece, 9 and 25 are observation pupils, 10 is a light splitting means, 23 is a Porro prism, 27 is a light guiding prism, and 11.28 is a condensing lens for photometry. ,1
2. 29 is a photometric element, and 3a and 29a are photometric sections. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] A finder optical system that uses an eyepiece to observe a real finder image formed by a dedicated objective lens system,
The objective lens system has a variable magnification means, the light beam that has passed through the objective lens system is divided into at least two light beams by a light splitting means, and one of the divided light beams is sent to a photometry section via a light guiding means. What is claimed is: 1. A finder optical system having a photometric means, characterized in that the light is guided to a light beam and used as a light beam for photometry.