JPH03236051A - Real image type erecting finder device and erecting prism - Google Patents

Abstract

PURPOSE:To sufficiently correct the curvature of field and to shorten the overall length of the finder by providing a positive power on the exit face of a 1st prism and the incident surface of a 2nd prism of a porro prism. CONSTITUTION:The 1st prism P 1 of the real image type erecting finder device for which the divided porro prism PP is used is formed with the incident surface 11, a 11th reflecting surface 12 and the exit surface 13. The 2nd prism P 2 is formed with the incident surface 21, the 21st reflecting surface 22 and 22nd reflecting surface 23 which are perpendicular to each other, the 23rd reflecting surface 24, and the exit surface 25. Both of the exit surface 13 of the prism P 1 and the incident surface 21 of the prism P 2 are constituted of spherical faces or aspherical faces having the positive power. Magnification can be in creased by parting the prisms P 1 and P 2 and shifting the imaging plane of the image by an objective optical system toward the incident surface side of the prism P 2.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a real image finder device, and more particularly to a real image erect finder using a split Porro prism.

"Prior art and its problems" In a real image type erect finder using a Porro prism, in order to increase the magnification, the prism is divided into two prisms, and the imaging plane of the objective lens is placed between the two divided prisms. is known to form. According to this, it is possible to use an eyepiece with a short focal length for observing the image on the image forming plane, and therefore it is possible to increase the magnification.

However, this finder device has a problem in that it becomes difficult to correct field curvature. In other words, the field flattener that corrects field curvature is most effective when placed near the imaging plane, but if the imaging plane is between the first prism and the second prism, then the field flattener Cannot be placed near a surface.

To solve this problem, a real image finder device using a split Porro prism has already been proposed, in which the entrance surface of the first prism has an optical function as a field flattener (Utility Model Application No. 63-226616). issue). However, this finder device still has the problem that it is difficult to further increase the magnification and shorten the overall length (length in the front-rear direction) of the finder.

According to the inventor's analysis, the causes are as follows.

That is, in the above-mentioned Japanese Utility Model Application No. 63-226616, both the exit surface of the first prism and the entrance surface of the second prism are flat. For this reason, both prisms cannot be separated. When separated, the second prism must be made larger in order to allow all the diffused emitted light from the first prism to enter.This causes the focal length of the eyepiece to become longer and the magnification to be sufficiently high (which is not possible). Moreover, since the optical path cannot be made in the lateral direction, it is also disadvantageous in shortening the length of the finder in the front-rear direction.

``Object of the Invention'' The object of the present invention is to obtain a real-image erecting finder that can increase magnification, sufficiently correct field curvature, and shorten the overall length of the finder. .

"Summary of the Invention" The present invention is based on the analysis of the problems of the above-mentioned Utility Model Application Publication No. 63-226616, by first giving positive power to the exit surface of the first prism to make it function as a capacitor. , it is possible to separate the first prism and the second prism. When both prisms are separated, the optical path length is increased (extended) in the lateral direction, and the overall length (length in the front-rear direction) of the finder can be shortened. Also, the imaging plane is
By moving the lens closer to the entrance surface of the prism, the focal length of the objective lens can be relatively increased and the focal length of the eyepiece lens can be shortened, thereby further increasing the magnification. Furthermore, providing positive power to the exit surface of the first prism has the same effect as arranging a field flattener near the imaging surface, and therefore can correct field curvature more effectively. can.

Next, the present invention provides positive power to the exit surface of the first prism by giving positive power to the entrance surface of the second prism so that it functions as a capacitor, and the imaging In addition to providing the surface on the entrance surface side of the second prism, it is possible to separate the first and second prisms without increasing the size of the second prism. Thereby, the second prism can be made smaller, the focal length of the eyepiece can be shortened, and the magnification can be increased.

Therefore, the finder device of the present invention is a finder device that observes an image formed by an objective optical system as an erect real image through a Porro prism divided into a first prism and a second prism and an eyepiece optical system, wherein the first prism The second prism has an entrance surface, an eleventh reflective surface, and an exit surface, and the second prism has an entrance surface, twenty-first and twenty-second reflective surfaces that are perpendicular to each other, and a twenty-third
In a real image type erect finder device that is provided with a reflective surface and an exit surface and forms an image by an objective optical system between the exit surface of the first prism and the entrance surface of the second prism, the exit surface of the first prism is The second prism is characterized in that it is composed of a spherical or aspherical surface that has power, and the entrance surface of the second prism is composed of a spherical or aspherical surface that has positive power.

In order to further increase the magnification, it is preferable to separate the first and second prisms so that their exit surfaces and entrance surfaces are separated, and position the imaging surface closer to the entrance surface of the second prism.

"Embodiments of the Invention" The present invention will be described below with reference to illustrated embodiments. 1 and 2 show an embodiment of the present invention. This finder device is
From the object side, it includes a second lens L1 with negative power, a second lens L2 with positive power, a Porro prism PP divided into a first prism P1 and a second prism P2, and an eyepiece L3.

The first prism P1 includes an entrance surface 11, an eleventh reflection surface 12, and an exit surface 13. The second prism P2 includes an incident surface 21, a 21st reflective surface 22 and a 22nd reflective surface that are perpendicular to each other.
It includes a reflective surface 23, a 23rd reflective surface, and an output surface 25. A field frame glass L4 serving as an imaging surface is located between the first prism P1 and the second prism P2, closer to the entrance surface 21 of the second prism P2.

In the present invention, the exit surface 13 of the first prism Pi and the second prism
The first feature is that both the entrance surfaces 21 of the prism P2 are constructed from spherical or aspherical surfaces having positive power. By giving positive power to the exit surface 13 and the entrance surface 21, it is possible to arrange the first prism P1 and the second prism P2 apart, and the first prism Pi and the second prism A second feature is that a field frame glass L4 is disposed between the prisms P2 close to the entrance surface 21 side.

The effects of the above two features are as follows. First, when the exit surface 13 and the entrance surface 21 are flat as in the conventional case, the light rays exit from the exit surface 13 (to diffuse, when the second prism P2 is separated from the first prism P1, the second prism P2 is separated from the first prism P1). This light beam cannot be taken in unless P2 is increased.For this reason, the first prism P1 and the second prism P2 cannot be installed substantially apart from each other.On the other hand,
When positive power is applied to the exit surface 13, it acts as a capacitor (therefore, the first prism P1 and the second prism P2
Even when separated, the light beam exiting from the exit surface 13 can be taken into the entrance surface 21.

And by applying positive power to the entrance surface 21,
The second prism P2 can be made smaller. Therefore, the first prism P1 and the second prism P2 can be separated. Separating the first prism P1 and the second prism P2 means extending the optical path length of the finder in the horizontal direction, so if the same optical path length is required, In addition, if positive power is applied to the 8-emitting surface 13 of the first prism PL, the same effect as arranging a field flattener near the field frame glass L4 will be obtained. Curvature can be corrected more effectively.

Next, the first prism P1 and the second prism separated in this way are
When the field frame glass L4 is placed closer to the second prism P2 side of the prism P2, the focal length of the eyepiece system becomes shorter and the focal length of the objective lens system becomes longer. This can be easily understood from the fact that the image formed on the field frame glass L4 by the objective lens system of the first lens Ll to the first prism P1 is observed by the eyepiece system of the second prism P2 and the eyepiece L3. Ru. Therefore, the magnification defined by the ratio of the focal lengths of the objective lens system and the eyepiece system can be increased. Furthermore, by applying positive power to the entrance surface 21, the second prism P2 itself can be made smaller.
It is effective to shorten the focal length of the eyepiece system.
Therefore, the magnification can be increased.

Furthermore, in the illustrated embodiment, the entrance surface 11 of the first prism P1
is composed of a spherical or aspherical surface with negative power,
The first prism P1 as a whole is a meniscus lens. Therefore, the meniscus lens can be placed at an abrasive position relative to the objective optical system composed of the first and second lenses L1 and L2, and the curvature of field can be reduced without causing spherical aberration, comatic aberration, etc. This has the advantage that it is possible to correct.

Further, in the illustrated embodiment, the exit surface 25 of the second prism P2 is configured as a flat surface, but it can also be made horizontally from a suitable spherical or aspherical surface to reduce the burden on the eyepiece L3 and make it smaller. It is possible to correct aberrations of the eyepiece L3.

"Effects of the Invention" As described above, the present invention provides a real-image erecting finder device using a split Porro prism, in which both the exit surface of the first prism and the entrance surface of the second prism are spherical or Since it is constructed from an aspherical surface, the curvature of field can be sufficiently corrected, and the length of the finder in the front-rear direction can be shortened. Furthermore, the magnification can be increased by separating the first and second prisms so that the image formation surface of the objective optical system is closer to the entrance surface of the second prism.

FIG. 1 is a perspective view and a plan view showing an example of an inder device.

Ll...second lens, L2...second lens, L3...
・Eyepiece, L4...Viewing frame glass (imaging surface), P
I...first prism, P2...second prism, PP
...Porro prism, 11...Incidence surface, 12...Eleventh reflection surface, 13...Emission surface, 21...Incidence surface, 2
2... 21st reflective surface, 23... 22nd reflective surface, 24
. . . 23rd reflection surface, 25 . . . output surface.

Claims (3)

[Claims] (1) A finder device for observing an image produced by an objective optical system as an erect real image through a Porro prism divided into a first prism and a second prism and an eyepiece optical system, wherein the first prism has an entrance surface , an eleventh reflecting surface and an exit surface, and the second prism includes an entrance surface, twenty-first and second reflecting surfaces that are perpendicular to each other, a twenty-third reflecting surface and an exit surface, and the exit surface of the first prism and the second prism. In a real image type erect finder device in which an objective optical system forms an image between the entrance surfaces of prisms, the exit surface of the first prism is composed of a spherical or aspherical surface having positive power, and the entrance surface of the second prism is A real-image type erect finder device characterized in that the image is constructed from a spherical or aspherical surface having positive power. (2) In claim 1, the first prism and the second prism are separated so that their exit surfaces and entrance surfaces are separated, and the second prism is
A real image type erect finder device characterized in that the image forming surface is positioned closer to the entrance surface side of the prism. (3) A first comprising an entrance surface, an eleventh reflection surface, and an exit surface.
a prism; a plane of incidence, a 21st and a 2nd plane at right angles to each other;
In an erecting prism consisting of a second prism having a second reflecting surface, a second reflecting surface and an exit surface, the exit surface of the first prism is composed of a spherical or aspherical surface having positive power, and the exit surface of the first prism is composed of a spherical or aspherical surface having positive power, An erecting prism characterized by having an entrance surface made of a spherical or aspherical surface with positive power.