JPH0644098B2 - Zoom lens with movable light splitting member - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a movable light splitting member, and a light splitting member for guiding a part of a photographing light beam to an observation system is sometimes used to change the magnification of the photographing system. In addition, the present invention relates to a zoom lens having a movable light splitting member of a TTL system in which the size of the entire observation system is reduced by moving on the optical axis of the photographing system.

(Prior Art) Conventionally, in a photographing system of a camera having a relatively small effective screen such as an 8 mm cine camera and a video camera, a light splitting member for guiding a part of a photographing light beam to an observation system is provided in a part of the photographing system. It is arranged.

For example, as a photographing system, a first lens group for focusing, which is fixed during zooming, a second lens group for zooming, a third lens group for correcting an image plane variation due to zooming, and an incident light flux in order from the object side as an imaging system. In many cases, a zoom lens consisting of five lens groups, a fourth lens group for making the afocal and a fixed fifth lens group, guides an aperture stop for limiting the light flux and a part of the photographing light flux to the observation system. Light splitting members for shining light are respectively arranged between the fourth lens group and the fifth lens group.

With such a zoom lens with a relatively effective screen,
Even when the aperture stop was fixed during zooming, the light splitting member and the observation system arranged near the aperture stop could be made relatively small.

On the other hand, in a TTL type photographic system having a large effective screen for 35 mm, in a photographic system having a standard angle of view, the size of the photographic system is reduced by changing the aperture diaphragm with zooming.

For example, Japanese Patent Application Laid-Open No. 57-20713 proposes a system in which an aperture stop is moved during zooming. However, in the zoom lenses proposed by these, the light splitting member is fixed and the aperture stop and the light splitting member move away from each other as the magnification changes. For this reason, for example, in order to guide a light beam having a predetermined angle of view to the observation system by using a light splitting member having a semi-transmissive mirror, the thickness of the light splitting member must be increased, and the aperture diameter of the observation system must be increased. There was a tendency for the entire zoom to become larger, which had to be increased.

(Object of the Invention) The present invention aims at downsizing of a light splitting member and an observation system in a zoom lens in which a light splitting member for guiding a part of a photographing light beam to the observation system is arranged in a part of the photographing system. It is an object of the present invention to provide a zoom lens having a movable light splitting member for downsizing the entire zoom lens.

(Main features for achieving the object of the present invention) A light splitting member for guiding a part of the photographing light flux to the observation system is arranged in a part of the photographing system, and the light splitting member is used when the magnification of the photographing system is changed. That is, it was moved parallel to the optical axis of the shooting system.

Another feature of the present invention is that the light splitting member is moved so that the imaging position of the observation image with respect to the observation system becomes constant.

A further feature of the present invention is that the light splitting member is moved integrally with the aperture stop in the photographing system or independently in the same direction.

The other features of the present invention will be described in detail in the description of each embodiment.

(Embodiment) FIGS. 1 and 2 are schematic views of an optical system according to an embodiment of the present invention.

In FIG. 1, reference numerals 1 and 2 denote first and second lens groups, respectively, as a variable power unit which moves with zooming. Second lens group 2
Has an aperture stop 3. 4 is a light splitting member having a semi-transmissive mirror 4a for guiding a part of the photographing light beam to the observation system, 5 is a third lens group fixed during zooming, 6 and 7 are reflecting mirrors, and 8 is a pentaprism. , 9 are eyepieces. In the present embodiment, a part of the photographing light flux that has passed through the variable power portion is split into an observation system by the semi-transmissive mirror 4a of the light splitting member 4, and is reflected by the reflecting mirror 6 substantially parallel to the photographing system. An observation image is formed on the image plane 10. Then, the observed image is observed after passing through the reflecting mirror 7, the pentaprism 8 and the eyepiece lens 9. In the present embodiment, the second lens group 2, the light splitting member 4, and the reflecting mirror 6 are integrally moved together with the first lens group 1 as indicated by the arrow in the figure during zooming. As a result, the image forming position of the observation image is always maintained on the first image plane 10 during zooming. Further, at the time of zooming, the aperture stop 3 and the light splitting member 4 are arranged close to the lens group closest to the image plane among the moving lens groups, and when zooming, the aperture stop 3 and the light splitting member 4 are moved integrally. 4 is prevented from increasing, and the diameter of the light beam incident on the observation system is prevented from increasing, thereby reducing the size of the observation system.

When the light splitting member 4 is arranged behind the variable power portion as in the present embodiment, the variable power system is configured by a converging system, which does not require an image forming system in the middle and simplifies the observation system. Is preferable. Further, the structure of this embodiment is suitable for the case where the photographing system and the camera are integrally formed, and it is not necessary to position the shutter immediately before the photosensitive surface, and it can be arranged immediately after the light splitting member. The aperture diameter of the camera can be made relatively small, and as a result, the lateral width of the camera can be substantially determined by the cartridge of the photosensitive material and the effective screen size, and the miniaturization of the entire camera can be easily achieved.

FIG. 2 is a schematic diagram of an optical system of an embodiment in which the light splitting member is arranged in the variable power portion. In the figure, 21,2
2, 23, and 24 are first, second, third, and fourth lens groups that move during zooming, 25 is a light splitting member, 26 is a reflecting mirror, and 27 is a Porro prism, which forms an image on the first image plane 29. The observation image thus obtained is observed by the eyepiece lens 28 as an erect image. Reference numeral 30 is an aperture stop. In this embodiment, the aperture stop 30, the third lens group 23, the light splitting member 25, and the reflecting mirror 26 are moved integrally in the direction of the arrow during zooming. Since the fourth lens group 24 that moves during zooming is arranged behind the light splitting member 25, the lens group 2 that moves to the reflection side of the light splitting member 25 during zooming is correspondingly arranged.
By providing 4 ', the image forming position of the observation image during zooming is always located on the first image plane 29.

By providing the light splitting member 25 together with the aperture stop 30 in the same lens group in the variable power portion, the effective diameter of the subsequent lens group can be reduced, and further increase of the effective system of the observation system can be prevented and the entire zoom lens can be prevented. We are aiming for miniaturization.

In this embodiment, since a lens group that moves during zooming is provided behind the light splitting member 25, the entire imaging system in front of the light splitting member 25 may be a divergent system or an afocal system.

In the first and second embodiments, the aperture stop and the light splitting member may be independently moved in the same direction during zooming, or they may be arranged in different lens groups. The purpose can be achieved. Further, in the present embodiment, the aerial image of the first image point may be observed, or the reticle may be arranged on the first image plane to observe the image on the reticle.
When observing an aerial image, it is preferable to dispose a condenser lens in the vicinity of the first image surface 10 because the light beam can be effectively used.

Next, FIG. 3 shows a cross-sectional view of a numerical example based on the example of FIG. 1 and an optical system of its photographing system.

In the numerical example, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are the i-th lens in order from the object side, respectively. It is the refractive index and the Abbe number of the glass.

The shape of the aspherical surface is x-axis in the optical axis direction and y in the direction perpendicular to the optical axis.
The axis is the positive direction of the light, the intersection of the lens surface vertex and the x-axis is the origin, R is the paraxial radius of curvature, H is the height from the optical axis, and A, B, C, D and E are non- Spherical coefficient, where x is the difference in the x-axis direction from the lens surface when the spherical surface that contributes to the determination of the focal length is extended, then x It is expressed by

In FIG. 3, I is the first lens group having negative refracting power, II is the second lens group having positive refracting power, III is the third lens group having negative refracting power, 31 is an aperture stop, and 32 is light splitting. Reference numeral 33 is a member, 33 is a shutter, 34 is a prism having a reflecting surface, 35 is a transparent focusing plate with Fresnel, 36 is a triangular prism having a convex surface, 37 is a triangular prism, and 38 is an eyepiece lens. The triangular prisms 36 and 37 form a Porro prism. The zooming is performed by moving the first and second lens groups I and II. Since the third lens group III is close to the photosensitive surface, the outer diameter of the lens may be cut according to the size of the photosensitive surface having the aperture, whereby the entire lens system can be downsized.

In the present embodiment, the observation system is also magnified at the same time due to the magnification change, and the observation image is set near the focusing screen 35 and remains unchanged.
Good observation is possible without any change in the diopter of the observation image.

In this embodiment, the aerial image may be observed without providing the focusing screen 35. At this time, it is preferable to dispose a condenser lens near the first image point because the light beam can be effectively used. In the present embodiment, the aperture stop 31 and the light splitting member 32 are brought close to each other, and are moved integrally during zooming to prevent an increase in the diameter of the light beam incident on the observation system and to reduce the size of the observation system. Further, since the parallel light beam and the oblique light beam intersect at the aperture stop 31, both light beams can pass through the light splitting member 32 within substantially the same effective diameter, so that the thickness of the light splitting member 32 is made thin and the necessary minimum. be able to.

In the present embodiment, the shutter 33 may be moved during zooming, or may be fixed if the size of the aperture has a margin. Further, the shutter 33 may be arranged behind the third lens group III. Further, in this embodiment, if a light emitting element or a light receiving element for automatic focus detection is arranged in a part of the observation system, for example, near the focusing screen 35, highly accurate automatic focus detection becomes possible.
Further, an automatic focus detection device may be arranged instead of the observation system. Further, by disposing the photometric element in the vicinity of the focusing screen 35 or at the same position as the optical axis of the observation system by using a semi-transmissive mirror, good evaluation photometry becomes possible.

According to the present invention, the light splitting member and the observation system are downsized by moving the light splitting member during zooming,
It is possible to achieve a compact zoom lens that can obtain a good observation image.

[Brief description of drawings]

FIGS. 1 and 2 are schematic views of an optical system according to an embodiment of the present invention, FIG. 3 is a lens sectional view of a numerical embodiment based on FIG. 1, and FIGS. FIG. 6 is a diagram of various types of aberration at wide-angle end, middle, and telephoto end zoom positions in a numerical example based on FIG. 1. In the figure, 3,30,31 are aperture stops, 4,25,3
Reference numeral 2 is a light splitting member, 10 and 29 are first image planes, 35 is a focusing screen, ΔM is a meridional image plane, and ΔS is a sagittal image plane.

Claims (4)

[Claims] 1. A light splitting member for guiding a part of a shooting light flux to an observation system is arranged in a part of the shooting system, and the light splitting member is used as an optical axis of the shooting system when the magnification of the shooting system is changed. A zoom lens having a movable light splitting member, characterized in that it is moved in parallel with. 2. The movable light splitting member according to claim 1, wherein the light splitting member is moved so that an image formation position of an observation image with respect to the observation system becomes a constant position. The zoom lens that I had. 3. The observation system has a reflecting member for reflecting a part of the photographing light beam split by the light splitting member in a direction substantially parallel to the optical axis of the photographing system, and the reflecting member is used for zooming. The movable light splitting member according to claim 2, wherein the member is moved integrally with the light splitting member, and the image formation position of the observation image is set on the observation side of the reflecting member. Zoom lens with. 4. The movable light splitting device according to claim 1, wherein the image pickup system has an aperture stop that moves integrally with the light splitting member or independently in the same direction. A zoom lens with a member.