JPH05241225A - Finder optical system having photometry means - Google Patents

Abstract

PURPOSE:To obtain a finder optical system having the finder of a high visual field magnification and a high visual field ratio, and a photometry means excellent in F-number proportionality and suitable for actual diaphragm photometry by properly setting each element of a focusing plate, a reflecting surface, etc., comprising the finder optical system and the arrangement of the photometry means. CONSTITUTION:A subject formed on a focusing screen 3 with a luminous flux finished pass a photographic lens 1, is reformed on a secondary image forming surface by a secondary image forming lens 6, and the photometry means metering the luminous flux diverged at a prescribed angle, against the optical axis of the photographic lens 1, out of the luminous fluxes from the focusing screen 3, is provided on a part of a finder system for observing the subject on the secondary image forming surface by an eyepiece 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system having photometric means, and in particular, it utilizes a secondary image forming method suitable for a so-called electronic camera of TTL optical type using an image pickup device such as an image pickup tube or CCD. The present invention relates to a finder optical system having photometric means.

[0002]

2. Description of the Related Art Conventionally, a single lens reflex camera using a penta roof prism for a 35 mm film has been greatly developed as an optimum one for system development.

However, an electronic camera using an image pickup device such as a CCD requires a lot of space for arranging an electric processing circuit in the rear part of the image pickup device, and the distance from the image plane of the photographing lens to the rearmost end of the camera is long. Is coming.

For this reason, the pupil position of the finder optical system must be extended rearward on the camera side, and a conventional viewfinder using a penta roof prism can provide a high visual field ratio and a high visual field magnification. Becomes difficult.

Under these conditions, a secondary image-forming finder is effective, and it is excellent in that it has a field of view magnification of about 0.8 times and a field of view of 90% or more even though it is small as in Japanese Patent Laid-Open No. 1-231013. A viewfinder for an electronic camera having excellent optical performance has been proposed.

FIG. 3 is a schematic view of a conventional secondary image-forming finder in which photometric means is incorporated. In the figure, 1 is a taking lens, 2 is a movable mirror, 33 is a focusing plate (focusing screen), 34 is a condenser lens, and 35 is a condenser lens.
Is a half mirror, 36 is an erector lens (secondary imaging lens), 37 is an eyepiece lens, 38 is a photometric lens, 39 is a photometric sensor, 10 is an optical low-pass filter, and 11 is an image sensor.

In the figure, a subject image is formed on the focusing plate 33 by the light flux from the taking lens 1. Then, the subject image formed on the focusing plate 33 is observed through the condenser lens 34 and the secondary image forming lens 36 on the secondary image forming surface by the eyepiece lens 37.

On the other hand, of the light flux from the subject image on the focusing plate 33, the light flux straightly traveling through the half mirror 35 is condensed by the photometric lens 38 and received by the photometric sensor 39.
In this way, conventionally, the photometric means (38, 38) in which the brightness of the subject image on the focusing plate 33 is arranged on the extension of the finder optical axis
In 39), the light was received and measured.

For this reason, it is possible to obtain a finder optical system having a feature that the photometric error due to the assembly precision of the photometric means and the variation of the exit pupil of the interchangeable lens is extremely small.

[0010]

However, in the structure in which the photometric means is arranged on the extension of the optical axis of the finder, the F-number (aperture angle) on the incident side of the photometric means and the aperture angle of the minimum F-number of the taking lens are set. There is a problem that the actual aperture metering cannot be performed unless and are not substantially equal.
Next, the reason will be described with reference to FIG.

FIGS. 4A and 4B are enlarged explanatory views of a part of the optical path of the finder optical system shown in FIG. 3, showing when the taking lens 1 has a large F number and when it has a small F number. There is.

As shown in the figure, when the photometric means (38, 39) is provided on the extension of the optical axis passing through the focusing plate 33, the focusing plate 33 is generally used as compared with the diffused light from the focusing plate 33. Since the light that is transmitted without being diffused (hereinafter referred to as the 0th-order light) is significantly stronger, the light amount detected by the photometric means is mainly 0.
Depends on the next light.

When the aperture of the taking lens is gradually opened (FIG. 4A), the amount of light reaching the image pickup surface 11 increases in proportion to the F number of the taking lens 1. The 0th order light that enters the photometric means is the taking lens 1
When the F-number of is smaller (brighter) than the F-number of the photometric lens 38, it no longer increases. (Fig. 4
(B)) Therefore, there is no correspondence between the change in the aperture of the taking lens 1 (change in the light amount on the image pickup surface) and the change in the light amount detected by the photometry means, and accurate actual aperture photometry cannot be performed.

Further, in order to use a photometric lens having an incident side F number close to the minimum F number of the photographing lens 1, it is practically F /
Approximately 2.8 is necessary, but especially when a large image sensor is used to obtain high resolution, the size of the focusing plate becomes large, and photometry for reducing the image on the focusing plate to the light receiving sensor. Since the magnification of the optical system also becomes large, the F number on the exit side becomes very small.

For example, when a 2 mm × 3 mm light receiving element (light receiving sensor) is used in an electronic camera having a 4/3 inch image pickup element, the light is emitted in order to set the incident side F number of the photometric optical system to F / 2.8. The side F number is about F / 0.5, and such a photometric optical system is very difficult to design.

The present invention has a finder with a high visual field magnification and a high visual field ratio by properly setting each element such as the focus plate, the reflecting surface, and the arrangement of the photometric means constituting the finder optical system, and An object of the present invention is to provide a finder optical system having photometric means suitable for actual aperture photometry with good number proportionality.

[0017]

In a finder optical system having a photometric means of the present invention, a subject image formed on a focusing screen by a light beam passing through a photographing lens is formed on a secondary image forming surface by a secondary image forming lens. Of the light flux from the focusing screen, a light flux that diffuses at a predetermined angle with respect to the optical axis of the photographing lens on a part of the finder system for re-imaging and observing the subject image on the secondary imaging surface with an eyepiece lens. It is characterized in that it is provided with a photometric means for photometry.

In particular, in the present invention, when the predetermined angle is θ, the condition 1 <1/2 sin θ <2.8 (1) is satisfied, and the predetermined angle is obtained by narrowing the diaphragm of the taking lens. The angle at which the light intensity changes substantially in proportion to the aperture diameter of the time stop, the light flux that has passed through the focusing screen is made incident on the secondary imaging lens through a reflecting surface, and the photometric means causes the secondary It is characterized in that it is incident on the imaging lens.

[0019]

Embodiment 1 FIG. 1 is a first embodiment in which a finder optical system having photometric means of the present invention is applied to an electronic still camera.
It is a principal part schematic diagram showing.

In the figure, 1 is a taking lens, 2 is a movable mirror which is retracted out of the taking optical path at the time of taking an image, 3 is a focusing plate (focusing screen) as a primary image forming surface, and an object image is formed by the taking lens 1. ing.

The matte surface of the focusing plate 3 in the present embodiment is of a type in which good diffusivity is emphasized rather than brightness so as to improve the proportionality to the F number of diffused light measured.

Reference numeral 4 is a condenser lens, and 5 is a fixed mirror, which is a total reflection surface mirror. Reference numeral 6 denotes an erector lens (secondary imaging lens), which forms a subject image on the focusing plate 3 on the secondary imaging surface 7a. Reference numeral 7 denotes an eyepiece lens for observing a subject image on the secondary image forming surface 7a.

Reference numeral 89 denotes a photometric means, which is arranged above the erector lens 6 and receives the light flux emitted from the focusing plate 3 in a predetermined direction to measure the brightness of the subject image on the focusing plate 3. .. The photometric unit 89 has a photometric lens 8 and a photometric sensor 9. Reference numeral 10 is an optical low-pass filter, and 11 is an image sensor such as a CCD.

In the present embodiment, the subject image formed on the focusing plate 3 by the taking lens 1 is re-imaged on the secondary image forming surface 7a by the erector lens 6 via the condenser lens 4 and the fixed mirror 5. .. Then, the subject image on the secondary image forming surface 7a is observed by the eyepiece lens 7.

The photometric means 89 arranged outside the finder optical path above the erector lens 6 receives the diffused light from the focusing plate 3 in a predetermined direction through the fixed mirror 5 to perform photometry. At this time, each element is set so that the central axis of the light measured by the photometric means 89 (the optical axis of the photometric lens 8) is at a predetermined angle, for example, about 19 degrees with respect to the finder optical axis passing through the focusing plate. There is.

Further, the photometric lens 8 is designed so that the F number on the incident side is F / 8. With these configurations, even if the aperture of the taking lens 1 is opened and the F number is small (bright) to F / 1.8, the 0th-order light from the focusing plate 3 hardly enters the photometric means 89, and By measuring only diffused light having good number proportionality, a photometric means suitable for actual aperture photometry is obtained.

Generally, when so-called Yabunirami photometry is performed, the F-number proportionality of the photometric output tends to deteriorate, but the main reason for this is that when the F-number of the luminous flux coming from the taking lens changes, it exits the focusing plate and enters the photometric optical system. There is a change in the ratio of the 0th-order light and the diffused light that enter.

According to the present invention, the misshapen angle θ within a predetermined range
The F number proportionality is improved by mainly measuring diffused light.

It is preferable that the yam angle θ satisfies the range of the conditional expression (1). If θ becomes larger than the range of the conditional expression (1), the amount of light incident on the photometric lens 8 becomes small, and the photometric accuracy deteriorates.
If θ becomes smaller than the range of the expression (1), 0th-order light from the focusing plate enters the photometric lens 8 when the F number of the taking lens is small, which is not good.

In addition to this, this embodiment has an advantage that the fixed mirror 5 for bending the finder light beam is not a half mirror, as compared with the finder optical system of FIG. 3, so that a bright finder can be obtained.

FIG. 2 is a schematic view of a main part showing a second embodiment when the finder optical system having the photometric means of the present invention is applied to an electronic camera. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, the photometric means 89 is arranged below the erector lens 6 as compared with the first embodiment of FIG. 1, and the fixed mirror 5 among the light flux from the focusing plate 3 is used by the erector lens 6
They are different in that they are bent downward and receive a reflected light beam, and other configurations are substantially the same.

As described above, there is an advantage that the camera height can be kept small by effectively utilizing the space below the erector lens 6.

[0034]

According to the present invention, as described above, by appropriately setting the respective elements such as the photometric means, the focus plate, and the reflecting surface which constitute the finder optical system, a finder having a high visual field magnification and a high visual field rate can be provided. However, it is possible to achieve a finder optical system having photometric means suitable for actual aperture photometry with good F-number proportionality.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an optical system according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of an optical system according to a second embodiment of the present invention.

FIG. 3 is a schematic view of a main part of a conventional finder optical system.

FIG. 4 is an explanatory diagram showing changes in the optical path when the aperture of the taking lens is changed.

[Explanation of symbols]

 1 Photographic Lens 2 Movable Mirror 3 Focus Plate (Focusing Screen) 4 Condenser Lens 5 Fixed Mirror 6 Elector Lens 7 Eyepiece 8 Photometric Lens 9 Photometric Sensor 89 Photometric Means 10 Optical Low Pass Filter 11 Image Sensor

Claims (4)

[Claims] 1. An object image formed on a focusing screen by a light flux passing through a taking lens is re-imaged on a secondary image forming surface by a secondary image forming lens, and the object image on the secondary image forming surface is formed. Among the light flux from the focusing screen, a photometric means for photometrically measuring a light flux diffused at a predetermined angle with respect to the optical axis of the photographing lens is provided in a part of the finder system observed by the eyepiece lens. Finder optical system that has. 2. A finder optical system having photometric means according to claim 1, wherein the condition 1 <1/2 sin θ <2.8 is satisfied, where θ is the predetermined angle. 3. The finder having photometric means according to claim 1, wherein the predetermined angle is an angle at which the light intensity changes substantially in proportion to the aperture diameter of the aperture when the aperture of the taking lens is closed. Optical system. 4. The light flux that has passed through the focusing screen is incident on the secondary imaging lens via a reflecting surface, and the photometric means measures the light that does not enter the secondary imaging lens. A finder optical system having the photometric means according to claim 1.