JPS60263101A - Finder optical system - Google Patents

Abstract

PURPOSE:To obtain the finder optical system with a high visual field rate and high visual field magnification which suits to an electronic camera, etc., with a relatively small photographic image plane by using two prisms in a specific shape in combination as a substitute for the conventional pentagonal roof prism. CONSTITUTION:The (x) axis is set on the incidence surface S1 of the 1st prism 10 in the optical-axis direction of a photographic lens 1, the (y) axis is set at right angles to the (x) axis, and the (z) axis is set at right angles to the incidence surface S1. A light beam E on the optical axis of a finder is incident on the incidence surface S1 of the 1st prism 10 nearly at right angles and reflected by the 1st reflecting surface S2 on which a reflecting film is vapor-deposited, reflected totally by the 2nd reflecting surface S1' almost in the same plane with the incidence surface S1, and then projected from the projection surface S3 of the 1st prism 10. Then, the light beam E is incident on the incidence surface S4 of the 2nd prism 11 and reflected by the roof surface S55' consisting of two reflecting surfaces S5 and S5' where a reflecting film is vapor-deposited, further reflected by the 4th reflecting surface S4' nearly on the same plane with the incidence surface S4, and then projected from a projection surface S6 nearly at right angles. Then, the light beam E projected from the projection surface S6 is incident on an ocular lens 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder optical system, and relates to a preferred finder optical system for a TTL optical type electronic camera using a solid-state image sensor tube such as a single-lens reflex camera, an image pickup tube, or a CCD in the q#. Meru0 Since then, single-lens reflex cameras using a penta roof prism for 35111jI film have developed greatly as the best option for system development! Ta.

FIG. 1 shows a schematic diagram of the configuration of a finder optical system of a typical single-lens reflex camera. In the figure, 101 is a rotatable total reflection mirror, 102 is a shutter unit, and 103
is the film surface, 104 is the 7 orcasing screen, 1
05 is a penta roof prism, 106 is an eyepiece, 10
7 is a pupil for observation. The finder optical system shown in Fig. 1 has a ratio of the image taken on the film surface to the object observed by the finder optical system, that is, a field of view of 90% or more.
It has excellent optical performance, with a field magnification r of 0.8 times or more when viewed north when a standard lens is attached.

This finder optical system has the characteristic that the entire device can be constructed relatively small.

However, recently, when the pentagonal roof prism is used in the finder optical system of an electronic camera using an 11w CCD image pickup body, it is difficult to achieve a field of view ratio and field magnification comparable to that of a conventional single-lens reflex camera. Furthermore, it becomes difficult to downsize the entire device. This is due to the following reasons.

(b) The effective screen of an image pickup body of % inches in diagonal length ratio is about 35% smaller than that of film, so if a conventional penta roof prism was used, the optical path length would be too long, resulting in a high field of view and a high It becomes difficult to obtain visual field magnification.

(b) A large amount of space is required to arrange the electric processing circuit at the rear of the image pickup body, and the distance from the image plane of the photographing lens to the rearmost end of the camera becomes long. For this reason, the pupil position of the finder optical system must be extended to the rear on the camera side, and as a result, it becomes difficult to obtain a high field of view and a high field of view magnification.

(c) Photographic lens Since a telecentric configuration is used for color separation of the gold image pickup body, the effective light beam from the photographic lens is spread out at the part where the finder optical path is divided, and the reflecting mirror becomes large.

2) Since a large amount of space is required to place optical components such as a low-pass filter, infrared cut filter, and protective glass in front of the image pickup body, the distance between the dividing point of the finder optical path and the image pickup surface must be large. The entire device becomes larger.

Next, for reference, FIG. 2 shows a schematic diagram of one row of the finder optical system in the case where it is intended to achieve a field of view of 90 degrees or more using a conventional Ben-Dach prism in an electronic camera. In the figure, 200 is a photographing lens, 201 is a dividing unit for dividing the optical path from the photographing optical path to the finder optical system, 202 is a low-pass filter, 203 is a shutter unit), 204 is the imaging surface of the imaging body, and 205 is an infrared cut 206 is a finder optical system unit including an erecting image system; 207 is a focusing screen; 2
08 is an electric processing circuit unit for imaging signals, and 209 is an observation pupil.

Generally, the larger the field magnification r is, the easier it is to observe the finder image. Field of view magnification r is the standard focal length of the photographic lens 1
-/, , focal length of the eyepiece lens t-f, is expressed as r-fa/f.

In order to increase the field magnification r, the focal length f of the standard lens is
, is approximately constant, it is necessary to reduce the focal length f of the eyepiece.

The eyepiece is arranged so that its front focal point is located near the viewfinder focusing surface of the finder optical system, so in order to increase the field magnification r, and to obtain an erect image from the haphazard screen to the eyepiece l. It is necessary to make the optical path length of the optical system as short as possible.

Now, suppose that the focal length f is set to Kf, -12,5-, which corresponds to the standard lens for a % index camera, and the field of view magnification r is set to 7-0.6, then the focal length f is f, -20,
It will be 8m.

In addition, to obtain a high field of view, K requires a focusing screen with the same size as the effective photographing screen and an erect image system large enough to establish an optical path that allows sufficient observation of the focusing screen. . Therefore, in Fig. 2, the optical path length from the 1st K focusing screen to the front principal point of the eyepiece is approximately equal to the focal length fi of the eyepiece. It is necessary to configure the lens so that the light from the focus/gear screen is 20.85 m 1 CL and enough Δ is incident on the eyepiece lens. Although a pentada prism that satisfies such requirements exists, as shown in the figure, the pentada roof prism 210 is used in the finder unit 206.
The eyepiece lens 211 must be placed adjacent to the exit surface of the pentadano prism 210. On the other hand, the observation pupil 209 has an eyepiece lens 211
, it is necessary to set it so that it is located far behind the rear end of the camera. However, since the position of the pupil is approximately the focal length from the rear principal point of the eyepiece, as shown in FIG. I'll have to take it seriously. This is very difficult. As described above, if a penta roof prism is used in a finder optical system of an electronic camera or the like with a relatively small effective screen, it becomes very difficult to achieve a high field of view and a high field of view magnification in terms of optical performance.

One object of the present invention is to provide a finder optical system having a high field of view and a high field of view magnification, which is suitable for electronic cameras having a relatively small photographic screen.

A further object of the present invention is to have a visual field ratio of 90% or more and a visual field magnification of 0.
The objective is to provide a finder optical system that is as small as 6.

The main feature of the finder optical system for achieving the object of the present invention is that the light from the object that has passed through the photographing system is reflected by a reflecting mirror and imaged on the finder imaging surface. In a finder optical system in which the upper finder image is observed with an eyepiece after passing through first and second prisms, the first prism i has an entrance surface S1 through which the light from the reflecting mirror enters, and the entrance surface S □The second reflecting surface 8 on approximately the same plane as the incident surface S
The second prism has a first reflecting surface S2 for reflecting in the 1' direction, an exit surface S3 for emitting the light reflected in the order of the first reflecting surface S2 and the second reflecting surface 81'. is an entrance surface S4 for making the light emitted from the exit surface S3 of the first prism enter, and a second prism for reflecting the light in the direction of a fourth reflecting surface 84' which is substantially on the same plane as the entrance surface 84.
one reflective surface s5. 8. It has an exit surface S6 for emitting light reflected in the order of the roof surface, the roof surface, and the fourth reflecting surface 84', and the shape of the eleventh second prism is arranged on the optical axis of the photographing system. The light from the exit surface S6
The light is emitted from a position substantially parallel to the optical axis of the photographing system and closer to the optical axis of the photographing system than the viewfinder imaging plane.

As described above, in the present invention, the object of the present invention is successfully achieved by combining two prisms having a predetermined shape instead of the conventional pentagonal roof prism.

Next, one embodiment of the finder optical system of the present invention will be described with reference to each drawing.

FIG. 3 is a schematic diagram of an embodiment in which the finder optical system of the present invention is applied to an electronic camera. In the same figure, 1
2 is a photographing lens, 2 is a movable mirror that retreats to the position indicated by the dotted line during photography, 3 is a low-pass filter, 4 is a shutter unit, 5 is a protective glass for the photographing object, 6 is the photographing surface, and 7 is a package for the photographing object. . Photographing lens 1t-passing and movable @
The light beam from the object reflected by I2 passes through an optical path correction plate 8 to make the aberration equal to the spherical aberration of the photographing system, and reaches the photographing surface 6.
The image is formed on the finder imaging surface 9 on the focusing screen, which is optically located at approximately the same position as . This object image becomes an erect image through the first series 10 and the second prism IIK having a .

The feature of the present invention is that in the configuration shown in FIG.
1 Preferably, the ray E is photographed so that the ray E travels on the optical axis and is reflected by the movable mirror 2 and travels on the finder optical axis so that when it exits from the second prism 11, it is approximately parallel to the optical axis of the photographing lens l. The angle is within ±10 degrees with respect to the optical axis of the lens 10.

This allows the viewfinder image to be observed in the same direction as the photographing lens l, making it easier to photograph moving objects in particular. Further, the shapes of the first and second prisms are specified so that the exit point of the light ray E from the second prism 11 is located closer to the optical axis of the photographic lens 1 than the finder image plane 9.

and 9, from the finder image forming surface 9 to the eyepiece 12t
By keeping the optical path length appropriate, high field of view and high field of view magnification can be easily achieved. Furthermore, the length of the light ray E from the point of incidence on the first prism 10 to the exit surface S6 of the second prism 11 is shortened to reduce the size of the finder optical system. Furthermore, a portion of the second prism 11 is located in a relatively large space near the imaging plane, thereby reducing the size of the entire camera.

Next, a perspective view of the first and second prisms 10.degree. 11 shown in FIG. 3 is shown in FIG. As shown in the figure, the first prism 10
has a triangular prism shape, and the second prism 11 has an edge I! D, it has a roof surface 855' consisting of reflective surfaces S5 and 85'.

The shapes of the first and second prisms 10 and 11 and the first and second prisms
FIG. 5 shows an optical path diagram of light incident on the prisms 10 and 11K. In the same figure, in order to explain the optical path, the coordinate system is defined as the incident surface S of the first prism 10, the optical axis direction fx axis of the photographing lens l on the field surface, the ty axis in the direction orthogonal to the X axis, and the incident surface 81 surface. The two axes are directions perpendicular to

In FIG. 5, a light ray E on the finder optical axis is incident approximately perpendicularly to the incident surface 81 of the first prism 100, is coated with a reflective film, is reflected by the first reflective surface S2, and is substantially on the same plane as the incident surface S1. After being totally reflected by the second reflecting surface S', the light is emitted from the first prism 10 through the exit surface S3. The half-rear ray E enters the second prism 1 through the incident surface S4 and passes through the second prism 1, which is composed of two reflective surfaces S and 85' on which a reflective film is deposited. ', and further reflected at a fourth reflecting surface 84' which is substantially on the same plane as the incident surface S4, and then exits substantially perpendicularly from the exit surface S6. The light ray E exiting from the exit surface S6 enters the eyepiece 12.

In this embodiment, the upper and lower images are reversed by the reflecting mirror 2 shown in FIG. 11
Invert the left, right, top, and bottom images on Goo plane S55', and then
The upper and lower images are reversed by reflection (3) 84' to obtain an erect normal image as a whole.

In this embodiment, the incident surface S1 and the second reflecting surface S1'
It is preferable to configure the incident surface S4 and the fourth reflective surface 84' on the same plane because it is easy to configure, but it is also possible to configure them with steps to change the optical path length and the exit position.

The first prism and the second prism may each be constructed by bonding two or more prism tubes together.

Note that the first prism 10 and the second prism 11 may be attached together or may be configured with a slight gap between them.

Next, the angles that determine the shapes of the first and second prisms 10 and 11 will be explained. As shown in FIG. 5, if the angle formed by the incident surface S1 of the first prism 10 and the first reflective surface S2 is determined by the angle cl formed by the ridge 1fiD of the roof surface of the A1 second prism 11 and the incident surface S1, the incident surface S and exit surface S3
The angle B formed by is determined from the formula B-45°-A+C. If the angle of incidence between the finder optical axis and each surface of the prism is as shown in the figure, tJ is the angle between the incident light and the outgoing light at the final reflection at the incident surface S4, e -A, f −2A, g −2A −
B, h-2A-CS j-2(A-C).

Next, numerical examples for specifying the shapes of the first and second prisms 10 and 11 according to the present invention are shown in Tables 1 to 3 based on the coordinates shown in FIG.

The direction of the normal line of each surface of the 11th-second prism io, nη is determined by the angle A in FIG. Determined. Therefore, these angles and arbitrary coordinates on each plane are listed in the table.

All of these numerical implementation columns 1 to 3 have a field of view ratio for an electronic camera with a 5-inch photographing surface.

An exit point P6' of the light IwE from the second prism 11 is a point P on the finder image plane 9. It is set in the minus direction on the wing axis, thereby shortening the finder optical path length and increasing the X-coordinate housing of the exit point P6', thereby achieving a high field of view ratio and high field of view magnification.

Table 1 Number matrix of the main points of the first and second prisms Table 2
Table 2 Numerical Example of the Principal Points of the First and Second Prisms 3 Numerical Example of the Principal Points of the First and Second Prisms Numerical examples are shown in Table 4.

As shown in FIG. 6, if the lens is constructed with four elements in three groups of positive, positive, positive, and negative refractive powers from the viewfinder side, an eyepiece lens with better aberration correction than K can be achieved.

Implementing this numerical value [In QIC, it is sufficient to set the radius of curvature R5 of the lens surface, the lens thickness or air gap, t ± 10%, the refractive index N of the lens glass, and the refractive index nν, t within ± 10% each. It is possible to achieve an eyepiece lens with the following aberration correction.

This numerical value implementation row 1 to 3 is set to the rear I of the exit surface of the second prism 11.
Place it at the M position and set the first diopter so that the diopter is 0 diopter.
, a numerical example when the numerical example in Table 4 is multiplied by the ratio of the optical path length of the second prism, and the visual field magnification r''ti5.

p4 Numerical Examples of Eyepieces/-1 Comparison with IK It is possible to construct a nine-sized finder optical system with high field of view and high field of view magnification. According to the present invention, an electronic camera with a relatively small effective screen has a high field of view and a high field of view magnification, and moreover, the space behind the camera can be used efficiently and the overall size of the camera can be easily miniaturized. .

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a part of the optical system of a conventional single-lens reflex camera, Fig. 2 is a schematic diagram of a part of the optical system when a penta roof prism is used in an electronic camera, and Fig. 3 is a schematic diagram of a part of the optical system of an electronic camera. 4 and 5 are explanatory diagrams of a part of FIG. 3, respectively, and FIG. 6 is a cross-sectional view of the eyepiece lens of the finder optical system according to the present invention. In the figure, 1 is a photographing lens, 2 is a movable mirror, 3 is a low-pass filter, 4 is a shutter unit, 5 is a protective glass, 6 is an imaging surface, 7 is a package for the photographing object, 8 is an optical path correction plate, 9
10 is a first prism, 11 is a second prism, 12 is an eyepiece lens, and 13 is a pupil position. Patent applicant Canon Co., Ltd. 6 Tomi 1 Z zu Ying 5 Den G zu 1 Meat 04051) 6

Claims (1)

[Claims] After the light from the object that has passed through the +11 photographing system is reflected by a reflecting mirror and focused on the finder surface, the finder surface on the 7-inner surface is 'M t , In the finder optical system in which the light passes through the K2 prism and is then observed with the eyepiece, the first prism enters the light from the reflecting mirror through the incident surface S and the incident surface S□, and directs the traveling light into the incident surface. The reflected light is emitted in the order of the first reflecting surface S2 for reflecting in the direction of the second reflecting surface 31/ which is substantially the same as the surface S1, the first reflecting surface S2, and the second reflecting surface S□'. The second prism has an exit surface 53t for the exit surface S3 of the first prism, and the second prism is substantially on the same plane as the entrance surface S4 and the entrance surface S4 for incident the light 1 emitted from the exit surface S3 of the first prism. A roof surface consisting of two reflective surfaces s and s5' for reflecting in the direction of the fourth reflective surface 84', and an exit surface S6 for emitting the light reflected in the order of the roof surface and the fourth reflective surface S7. The shape of the eleventh second prism is approximately parallel to the optical axis of the photographing system when light on the optical axis of the photographing system exits from the exit surface S6, and ν more than the viewfinder imaging plane. The finder optical system is unique in that it is configured to emit light from a position close to the optical axis of the photographing system.