JPH0216532A - Optical system for photography and observation - Google Patents

Abstract

PURPOSE:To eliminate parallax unlike a conventional compact camera, to eliminate the need for expensive components such as a pentagonal prism, and to make a camera compact by allowing a photography system and a finder system to share a negative front group lens. CONSTITUTION:The front group lens 1 with negative refracting power that the photography system and observation system share is provided and a movable mirror 3 or prism is arranged in front of the lens 1. The mirror 3 or prism is put off the optical axis of the front group except during photography and a subject is observed through the virtual image finder consisting of the front group 1 and an observation system rear group lens with positive refracting power which shares the optical axis with the front group 1. When a photograph is taken, the mirror 3 or prism is moved onto the optical axis of the front group 1, light from a subject which is passed through the front group 1 is reflected, and its image is formed through a photography system rear group lens 4 and photographed. The photography and observation optical system is constituted as mentioned above to eliminate the parallax and the low-cost, compact photography and observation optical system of a new type which is not found before is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical system for a photographic camera having a non-balarax optical system for photographing and observing, and particularly to an optical system having a simple configuration.
Concerning optic system.

(Prior Art) In a camera that has a finder optical system separate from a photographic optical system, when a subject becomes close, the range observed through the finder differs from the range captured in the photograph. This phenomenon is known as balarax. This occurs because the optical axis of the photographing system and the optical axis of the finder system are different, as shown in FIG. 3, and cannot be avoided as long as there is a distance between the optical axes. For this reason, in so-called compact cameras, in addition to the normal field of view frame, there is a field of view frame especially for short-distance use, but this has the drawback that it becomes complicated due to the large number of frames, and the focus is on the shooting center and the viewfinder system. The misalignment still exists, making it difficult to use.

In addition, - eye reflex cameras use a quick return mirror to guide the image from the photographing lens to the viewfinder (TTL viewfinder), so the above variation does not occur, but in order to obtain an erect image, It is necessary to use parts such as a pentaprism, which increases the cost.

(Problems to be Solved by the Present Invention) An object of the present invention is to obtain a new type of photographing/observation optical system that is free from variation, low in cost, and compact, and which has never been seen before.

(Means for Solving the Problem) In order to achieve the above object, the present invention provides a front group lens with a negative refractive power that is shared by the photographing system and the observation system, and a movable mirror or prism is arranged behind it. At other times, the mirror or prism is avoided from the optical axis of the front group, and a virtual image finder consisting of the front group and an observation system rear group lens with a positive refractive power that shares the optical axis with the front group is used. Observe the subject, and when photographing, move the mirror or prism onto the optical axis of the front group, reflect the light from the subject that has passed through the front group, and then form an image with the rear group lens of the photographing system and take the photograph. Configure the photographing/observation optical system as described above.

(Example) Examples of the optical system of the present invention will be shown below.

FIG. 1 is a cross-sectional view of one embodiment of the optical system of the present invention when observed. A photographer can observe a subject using an inverted Galilean finder made up of a negative lens 1 and a positive lens 2 that share the same optical axis.

FIG. 2 is a cross-sectional view of the same optical system when photographing. The light beam that enters the negative lens 1, which is common to the finder system, is reflected by the mirror 3, passes through the rear group lens 4 of the photographing system, is reflected again by the fixed mirror 6, and heads toward the film surface 7. The mirror 3 is a quick return mirror, and returns to the light state shown in FIG. 1 as soon as photography is completed. In the example, the optical axis is bent at right angles by a mirror, but the optical axis before reflection and 2
As long as the optical axes after the second reflection are parallel, they do not necessarily have to be at right angles. Note that 5 is an aperture.

In this shooting system, focusing is performed after the shooting lens system.
It is best to do this in 4. With a photographic lens system, the angle of view becomes slightly smaller during focusing, but because the apparent field of view of a finder system does not change, the field of view of the finder changes and becomes larger. , field of view is usually 80-90%
It is set so that there is a margin, and even if there is a slight change,
No problems arise.

Further, in the present invention, it is also possible to display a lighting type display on the finder system. FIG. 4 shows a cross-sectional view of the optical system when a daylight display system is adopted, and the viewing frame on the daylight window 8 is as follows:
It is superimposed on the subject image by the half mirror 11 via the fixed mirror 9 and the target lens 10, but the half mirror 11 for daylighting is placed at the same position as the quick return mirror during shooting to avoid hitting the quick return mirror 3. ! 3
It is placed behind ``.

Furthermore, in the optical system of the present invention, the rear group of the finder system may constitute an Albada system to display the field of view.

FIG. 5 shows a sectional view of an embodiment employing the Albada system.

A lens 12 in the rear group of the finder system has a half mirror surface 13, and a frame 14 is deposited on the positive eyepiece lens 2. The photographing lens system used is the same as in the first embodiment.

Furthermore, in the present invention, it is desirable that 0.5<-f, /f<3 be satisfied, where f is the focal length of the photographing system, and f is the focal length of the negative front group shared with the finder. . If the upper limit of this condition is exceeded, the effective system of the front group becomes large, making it difficult to arrange a quick return mirror. On the other hand, if it becomes smaller than the lower limit, the photographing system will have an extremely inverted telephoto lens arrangement, and the overall length will become too long.

A prism may be used instead of the quick return mirror, and the prism may be inserted and removed on the finder optical axis.
When a prism is used instead of a mirror, the prism is oriented perpendicular to the plane of the paper, or in the embodiments shown in FIGS. Move it above to insert/remove.

As for the position of the shutter, either an aperture-cum-shutter may be placed at the aperture 5 position in the drawing (lens shutter type), or a focal brain shutter may be placed just in front of the film surface 7.

Further, it is preferable that the mirror (prism) that guides the light to the photographing system be a total reflection mirror, since the color balance will be disrupted if it is a half mirror.

Below, numerical data of the optical system of the present invention will be shown.

Note that each symbol in Table 2 indicates that R is the radius of curvature of each refractive surface, D is the distance between the refractive surfaces, N is the refractive index of the lens material, and νd is the Abbe number.

Example 1 Photography system Focal length 50. OF number 4.5 Half angle of view 23.4°50.4g4 25.182 17.250 -23.732 -29.531 17.079 102.71 -20.047 f = -100 Finder system 50.484 D Na 2.0 1.51633 64.130.0 3.0 1.6968Q 55.53.0 2.0 1.60342 3g, 02.0 3.0 1.51633 64.1-f1/f=
2 N-v d 2.0 1.51633 64.12
25.182 35.03 155.0
0 3.0 1.492 55.04
-150.00 Finder magnification 0.73 Paraxial diopter -〇, 98 Dayopter example 2 (Photographing system is the same as example 1) Finder system RD Nd 1 50.484 2.0 1.5
1633 64,12 25°182 2
9.03 -150.00 2.0
1.492 55.04 2g, 0
00 10.05 oo
2.0 1.492 55.06
-24.000 Finder magnification 0.57 Finder system paraxial diopter - 1,04 day optic - Albada system paraxial diopter - 1,06 day optic - 4th side is a half mirror - 15th side is a frame vapor deposition surface.

(Effects of the Invention) As described above, in the present invention, since the negative front group lens is shared by the photographing system and the finder system, there is no variation unlike in conventional compact cameras, and moreover, the pentaprism etc. There is no need to use expensive parts. Furthermore, since the negative front group lens is common, the number of lenses is also reduced.

Furthermore, since there is no finder window on the front of the camera, this negative lens can have a fairly large diameter, so the finder magnification can be increased and the performance as a finder can be improved.

Furthermore, the optical axis of the photographic optical system is bent by a mirror, which is advantageous in making the camera compact.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the optical system of the present invention when observed;
Figure 2 is a cross-sectional view of the same optical system when photographing, Figure 3 is an explanatory diagram of Balarax, Figure 4 is a cross-sectional view of the optical system of an example in which a daylight display system is used as the finder system, and Figure 5 shows a cross-sectional view of an embodiment employing the Albada system. 1: Negative lens 2: Eyepiece positive lens 3; Mirror 4: Rear group lens of photographing system 5: Aperture
6.9: Fixed mirror 7: Film surface 8:
daylight window

Claims (1)

[Claims] A movable mirror or prism is arranged behind a front group lens with negative refractive power that is shared by the photographing system and the observation system, and the mirror or prism is avoided from the optical axis of the front group except when photographing, and the front group lens is The object is observed by a virtual image finder composed of a rear observation group having a positive refractive power that shares the optical axis with the front group, and when photographing, the mirror or prism is moved onto the optical axis of the front group, A photography/observation optical system characterized by reflecting light from a subject that has passed through a front group, and then forming an image with a rear photography group to take a picture.