JPH0795182B2 - Photometric optical system of single-lens reflex camera - Google Patents

Description

The present invention relates to a photometric optical system for a single-lens reflex camera,
In particular, when a light beam from the field is guided onto the surface of the light receiving means for photometry, the condenser lens and the light receiving means are efficiently arranged behind the exit surface of, for example, a pentaprism for changing the optical path. The present invention relates to a photometric optical system of a single-lens reflex camera for photometry.

(Prior Art) Conventionally, in the photometric optical system of a single-lens reflex camera, various photometric optical systems have been proposed in which a condenser lens and a light receiving unit are arranged behind the exit surface of a pentaprism to perform photometry.

In such a photometric optical system, the condenser lens and the light receiving means are arranged behind the exit surface of the pentaprism, so that the light flux from the finder image formed on the focusing screen can be relatively easily guided to the light receiving means. Can be metered.

Therefore, it has many advantages that the photometric sensitivity distribution can be easily controlled, that almost the entire field of view to be photographed can be easily photometered, and that it is not bothersome to see from the viewfinder. There is.

In addition to these photometric optical systems, various photometric optical systems have been proposed in which a light receiving means is arranged on a portion other than the exit surface of the pentaprism to perform photometry.

For example, FIGS. 4 to 7 are each a schematic view of an optical system of a photometric optical system for performing photometry by arranging light receiving means on a portion other than the exit surface of a conventional pentaprism.

In FIGS. 4 to 7, 1 is an imaging lens, 2 is a quick return mirror (hereinafter referred to as “QR mirror”), 3 is a focusing plate, 4 is a penta prism, 5 is an eyepiece lens, and 7 is a light receiving means. , 8 is a film surface, 9 is an optical axis of a photographing lens, 10 is an optical axis of a finder, 11 is an optical axis of a photometric system, 14 and 16 are reflection members, and 13, 15 and 17 are condenser lenses.

FIG. 4 is a schematic diagram showing an example of a photometric optical system that receives and reflects the reflected light from the film surface 8 or the shutter curtain surface in the field light. Since the photometric optical system in the figure performs photometry when the QR mirror 2 is raised, there is an advantage that there is no shift in the photometric value due to the time difference between photometry and shooting. However, since the reflection on the film surface 8 or the shutter curtain surface is used, there is a drawback that the photometric value changes to a difference in reflectance between the film surface 8 and the shutter curtain surface.

Further, in the photometric optical system in the figure, since the position where the light receiving means 7 is arranged is the bottom or side of the camera or the back surface of the QR mirror 2, the film surface corresponding to the field area to be photometered in any case. 8 or the shutter curtain surface cannot be directly faced, and the light receiving means 7 can be arranged only at a position where the film surface 8 or the shutter curtain surface can be seen at a considerable angle, and thus a desired photometric sensitivity distribution can be obtained. It has the drawback that it is difficult to perform.

FIG. 5 is a schematic diagram showing an example of a photometric optical system in which a reflecting member 14 is fixedly provided behind the QR mirror 2 and a light beam from a photographing lens is guided to the light receiving means 7 to perform photometry. In the photometric optical system in the figure, the light receiving means 7 can be positioned not in a position where the film surface is obliquely seen in the photometric optical system shown in FIG. With respect to the central portion, there is an advantage that a desired sensitivity portion can be obtained.

However, there is a drawback in that it is not possible to make the reflection member 14 sufficiently large due to a problem in the space where the reflection member 14 is arranged, and therefore it is not possible to perform photometry over almost the entire field of view.

FIG. 6 is a schematic view showing an example of a photometric optical system in which the reflecting member 16 and the light receiving means 7 are arranged in the vicinity of the focusing screen 3 and the luminous flux from the photographing lens is guided to the light receiving means 7. The photometric optical system in the figure has an advantage that a desired photometric sensitivity distribution can be easily obtained depending on the size of the reflecting member 16.

However, there is a drawback that the finder image becomes dark because the amount of light to the finder system becomes small, and it is difficult to arbitrarily change the photometric sensitivity distribution.

FIG. 7 is a schematic diagram showing an example of a photometric optical system for measuring the field light by disposing the condenser lens 17 and the light receiving means 7 on a part other than the exit surface of the pentaprism 4. In the photometric optical system shown in the figure, since the light beam is emitted from the area of the pentaprism 4 where the light ray is not normally emitted, there is a disadvantage that these portions are visible from the finder and it is troublesome.

Further, since the focusing lens 3 and the light receiving means 7 are arranged on the exit surface of the pentaprism 4 so that the focusing screen 3 can be seen more obliquely as compared with the photometric optical system for measuring the field light, it is desirable. It has a drawback that it is difficult to obtain a photometric sensitivity distribution.

On the other hand, FIG. 3 is a schematic view of a photometric optical system for performing photometry by arranging the condenser lens 12 and the light receiving means 7 behind the exit surface of the above-mentioned conventional pentaprism. In the figure, the same elements as those shown in FIG. 4 are designated by the same reference numerals.

In the figure, an ordinary circular condenser lens 12 is arranged behind the pentaprism 4 and a light receiving means 7 is arranged further behind the condenser lens 12 so that a subject image formed on the focusing screen 3 is condensed by the condenser lens 12. The light is guided to the light receiving means 7 for photometry.

At this time, the condenser lens 12 is arranged above the eyepiece lens 5 so that the light beam emitted from the ineffective light beam portion above the light beam for observing the finder image on the exit surface of the pentaprism 4 is guided to the light receiving means 7. It is configured to measure light.

A condenser lens behind the exit surface of the pentaprism 4 shown in FIG.
The photometric optical system for arranging 12 and the light receiving means 7 for photometry can relatively easily photometer almost the entire screen as compared with the photometric optical system shown in FIGS. 4 to 7. In addition, since it can be arranged at a position not far from the finder optical axis 10 and the focusing screen 3 which is the focal plane can be seen from a position close to the front, a desired sensitivity distribution can be easily obtained. There was an advantage.

However, on the other hand, since the light is measured using the condenser lens 12 having a small effective portion at a position away from the focusing screen 3,
There is a drawback that the amount of light guided to the light receiving means 7 is insufficient, and photometry of a low-luminance subject tends to be difficult.

Further, in the photometric optical system shown in the figure, since the lens having the normal circular effective diameter is used as the imaging lens 7, the area of the non-effective portion of the finder light flux on the exit surface of the pentaprism 4 is fully utilized. However, the amount of light guided to the light receiving means 7 tends to be insufficient, and it is difficult to perform photometry on a low-luminance subject.

Further, when such a condenser lens 12 is used, the optical axis 11 of the photometric system of the condenser lens has to be arranged at a position relatively distant from the position of the finder optical axis 10, so that the axis of the condenser lens 12 There is also a drawback that the condensing state of the light beam on the surface of the light receiving means is deteriorated due to the influence of external aberration, and it becomes difficult to obtain a desired photometric sensitivity distribution.

(Problems to be Solved by the Invention) According to the present invention, when a condenser lens and a light receiving unit are arranged behind the exit surface of a pentaprism and the field light is measured, the finder light flux on the exit surface of the pentaprism is ineffective. It is an object of the present invention to provide a photometric optical system of a single-lens reflex camera that can effectively use a light flux from a lens section and can obtain an arbitrary photometric sensitivity distribution with a compact configuration as a whole.

(Means for Solving the Problems) Other than the effective light flux for finder image observation that has passed through the prism, using a condenser lens and a light receiving means arranged behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera that receives the light flux of the object to measure the field, at least a part of the condensing lens on the finder optical axis side is notched, and the notch part of the condensing lens is a finder image. This means that the observation light beam is placed close to the optical axis of the finder.

(Embodiment) FIG. 1 is a schematic view of a photometric optical system of a single-lens reflex camera showing an embodiment of the present invention. In the figure, 1 is a taking lens, 2 is a QR mirror, 3 is a focusing plate, 4 is a pentaprism, 5 is an eyepiece lens, and 6 is a condenser lens which is a feature of the present invention and a part of the viewfinder optical axis 10 side is cut away. There is. 7
Is a light receiving means, 8 is a film surface, 9 is an optical axis of a photographing lens,
11 is the optical axis of the photometric optical system.

In this embodiment, the light flux from the object field that has passed through the taking lens 1 is reflected by the QR mirror 2 to form an image on the focusing screen 3. Then, the field light from the focusing screen 3 is guided onto the light receiving means 7 by the condenser lens 6 arranged above the eyepiece lens 5 behind the exit surface of the pentaprism 4 to measure the field light. Is going.

The features of the present invention will be described below in comparison with the photometric optical system of the conventional example shown in FIG. 3, which is similar to the embodiment of the present invention.

FIG. 2 shows a condenser lens 6 used in the photometric optical system according to the present invention.
It is explanatory drawing which shows and the light-receiving means 7. The condenser lens 6 of this embodiment has a part of the viewfinder optical axis 10 side cut away.

In this embodiment, as shown in the figure, the lower part of the condenser lens 6, that is, the finder optical axis 10 side is abraded by a plane perpendicular to the plane including the photometric system optical axis 11 and the finder optical axis 10.

FIG. 8 is an explanatory view of the photometric optical system according to the embodiment of the present invention shown in FIG. 1 when viewed from the rear of the exit surface of the pentaprism.

FIG. 9 is an explanatory view of the conventional photometric optical system shown in FIG. 3 as viewed from the rear of the exit surface of the pentaprism.

In FIGS. 8 and 9, the broken line 18 indicates the finder effective portion, and the condenser lenses 6 and 12 are both arranged above the finder effective portion so as not to interfere with the finder effective portion. d1 and d2 are the distances from the finder optical axis 10 to the photometric system optical axis 11 on the exit surface of the pentaprism.

In FIGS. 8 and 9, the eyepiece 5 and the light receiving means 7 are omitted for simplicity.

In this embodiment, as shown in FIG. 8, the diameter of the condenser lens 6 is increased, and the lower portion of the condenser lens 6 is scraped off, so that the penta prism as compared with the conventional example shown in FIG. The area above the finder effective portion 18 of the exit surface is used more effectively.

That is, in FIG. 8, the amount of light guided to the light receiving means 7 can be obviously increased as compared with FIG. 9, and as a result, it is possible to improve the photometric accuracy of a low-luminance subject.

Further, the distance d1 between the finder optical axis 10 and the photometric system optical axis 11 on the exit surface of the pentaprism in FIG. 8 and the finder optical axis 10 and the photometric system optical axis 11 on the exit surface of the pentaprism in FIG.
Since the distance d2 is clearly d1 <d2, the present invention shown in FIG. 8 makes it possible to arrange the light receiving means 7 below the conventional structure shown in FIG. A compact configuration can be achieved.

Further, since the light receiving means 7 can be more directly faced to the focusing screen 3, that is, the object scene, the photometric sensitivity distribution can be controlled more easily.

By the way, as described above, the condenser lens 6 in FIG. 8 has a larger diameter than the condenser lens 12 in FIG. Therefore, in order to increase the amount of light guided to the light receiving means 7 and to make the photometric system compact, the imaging magnification of the photometric optical system shown in FIG. 8 is made substantially equal to the imaging magnification shown in FIG. Since the focal length of the condenser lens 6 in FIG. 8 must be made substantially equal to the focal length of the condenser lens 12 in FIG. 9, the condenser lens 6 in FIG.
It becomes necessary to further improve the optical performance of.

FIG. 10, FIG. 11 and FIG. 12 are optical path diagrams when the condenser lens 6 is composed of a biconvex lens having two spherical surfaces.

FIG. 10 shows the points at the upper part of the image capturing screen of the condenser lens, FIG. 11 shows the points at the center of the image capturing screen of the condenser lens, and FIG. 12 shows the image formation state of the points at the lower part of the image capturing screen of the condenser lens. There is.

When the condensing lens 6 is composed of one biconvex lens whose both lens surfaces are spherical, various aberrations occur as shown in FIGS. 10 to 12, and the image forming state is not always good.
In particular, in FIG. 12, the image forming state is considerably deteriorated by the light rays that have passed through the lower portion of the image forming lens 6. Further, assuming that the blur amount as shown in FIG. 10 can be tolerated, sufficient performance can be obtained by removing light rays passing through the lower region of the condenser lens 6 in FIGS. 11 and 12. become.

FIGS. 13, 14, and 15 are optical path diagrams when the lower portions of the condenser lenses shown in FIGS. 10, 11, and 12 are peeled off as in this embodiment.

In FIGS. 13, 14, and 15, a shaded portion 30 is a portion obtained by removing the lower portion of the condenser lens 6 according to the present invention, and a broken line 31 is a condenser lens 6.
2 shows a light beam that is removed when the shaded portion 30 in the lower part of FIG.

By removing the lower part of the condenser lens 6 as shown in FIGS. 13, 14, and 15, it is possible to remove the light beam 31 passing through the lower region of the condenser lens 6, thereby forming an image. Can be improved and the optical performance can be further improved.

FIGS. 16, 17 and 18 are optical path diagrams when the surface of the condenser lens 6 on the exit side of the penta prism is an aspherical surface and the other surface is a spherical surface in the present invention.

In FIGS. 16, 17, and 18, the same elements as those shown in FIG. 13 are designated by the same reference numerals.

FIG. 16 shows a point on the upper part of the photographing screen of the condenser lens, FIG. 17 shows a point on the central part of the photographing screen of the condenser lens, and FIG. 18 shows an image forming state of a point on the lower part of the photographing screen.

Generally, if the screen of the condenser lens 6 is a spherical surface, the thirteenth and first
4, As shown in Fig.15, some aberration remains. Therefore, even though it can be used for an average photometry system that averages the field, it is possible to use a partial photometry system that measures a part of the field or the field. It has been difficult to use in a photometric system of a spectrophotometric system which divides light into a plurality of regions and performs photometry.

Therefore, various proposals have heretofore been made to satisfactorily remove aberrations by using an aspherical surface on one lens surface of the condenser lens.

Each of FIGS. 16, 17, and 18 is an example in which the lens surface of the condenser lens 6 on the pentaprism exit surface side is an aspherical surface in order to eliminate the above-mentioned aberrations. Even if an aspherical surface is used for one lens surface of the condenser lens 6 as shown by the dotted line in Fig. 18, if the effective diameter is sufficiently larger than the focal length, the off-axis aberration in the region shown by the broken line 31 in Fig. 18 It becomes difficult to make a good correction of.

Therefore, even if one lens surface of the condenser lens is an aspherical surface, it is not possible to remove the lower region of the condenser lens 6 shown by the dotted lines in FIGS. 16, 17, and 18 as in the present invention. It is very effective in improving

If aspherical surfaces are used for both lens surfaces of the condenser lens 6, off-axis aberrations can be corrected even better.

FIG. 19 and FIG. 20 are schematic views of main parts when seen from the rear of the exit surface of the pentagonal prism of another embodiment of the present invention.
In FIGS. 19 and 20, the same elements as those shown in FIG. 8 are designated by the same reference numerals.

In FIG. 19, 11 and 11 'are optical axes of the photometric system, and 19 and 19' are condenser lenses according to the present invention, and the viewfinder optical axis side is removed.

In this embodiment, two condenser lenses 19 and 19 'with the finder optical axis side removed are arranged at positions on the rear side of the exit surface of the pentaprism 4 that do not interfere with the left and right finder light beams, and the field light is measured. ing.

In FIG. 20, reference numerals 20 and 20 'are condenser lenses according to the present invention, and in this embodiment, the finder optical axis side and other side surfaces are removed.

Also in this embodiment, as in the case of FIG. 19, two condensing lenses are arranged so that the left and right finder luminous fluxes behind the exit surface of the pentaprism 4 are removed so as not to interfere with the finder optical axis. 20 and 20 'are arranged to measure the field light.

In particular, in the present embodiment, the ineffective areas of the finder light flux on the left and right of the exit surface of the pentaprism 4 are used more effectively,
Considering the shape of the ineffective area of the finder light flux, not only the finder optical axis side of the condenser lenses 20 and 20 'but also the lower side thereof is removed as shown in FIG.

In each of the configurations of FIG. 19 and FIG. 20, the left side and the right side of the photographic screen are measured separately, and if the entire screen is measured, the photometric sensitivity distribution caused by not facing the reticle The imbalance can be dealt well.

The present invention can also perform photometry by combining the arrangement of the condenser lens shown in FIG. 19 or 20 with the arrangement of the condenser lens shown in FIG.

FIG. 21 is a schematic view of a photometric optical system of a single-lens reflex camera showing another embodiment of the present invention. First in the figure
The same elements as those shown in the figure are denoted by the same reference numerals. 21,2
Reference numeral 2 denotes a convex lens in which a part of the optical axis side of the finder has been removed. In this embodiment, these two convex lenses 21 and 22 form a condenser lens.

In the present embodiment, as shown in the same figure, the condenser lens is composed of two convex lenses 21 and 22 whose lower part is scraped off to correct aberrations satisfactorily.

FIG. 22 is a point at the upper part of the photographing screen of the condenser lens of the embodiment shown in FIG. 21, FIG. 23 is a point at the center of the photographing screen of the condenser lens of the present embodiment, and FIG. 24 is a collection of this embodiment. The respective imaging states of the points at the bottom of the photographing screen of the optical lens are shown.

22, 23, 24 in FIG. 21, 21 and 22 are convex lenses respectively constituting a condenser lens, the shaded portion 40 is a portion to be scraped off,
A broken line 41 is a light beam removed when the lower parts of the convex lenses 21 and 22 are scraped off.

When the two lenses are abraded as in the present embodiment, the lens surfaces to be abraded do not necessarily have to be the same plane, and may be planes with steps.

Further, even when only one lens is used as a condensing lens, the abrading surface of the lens does not necessarily have to be a flat surface, and a shape considering the arrangement of other parts, for example, a stepped shape or a curved shape. Is also good.

(Effects of the Invention) As described above, according to the present invention, when the field of view is measured using a light flux other than the finder effective light flux that passes through the exit surface of the pentaprism, at least the finder optical axis is located behind the exit surface of the pentaprism. By providing a condensing lens and a light-receiving means with part of the side removed, and disposing the condensing lens close to the viewfinder optical axis, a good image formation state can be achieved over almost the entire area of the shooting screen, and a sufficient amount of light is easy. In addition, it is possible to achieve a photometric optical system of a single-lens reflex camera which is easy to be made compact and which can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical system of a single-lens reflex camera showing an embodiment of the present invention, and FIG. 2 is an enlarged view of a main part when the condenser lens according to the present invention shown in FIG. Figure 3 ~
FIG. 7 is a schematic view of a conventional photometric optical system, and FIG.
FIG. 9 is an explanatory view of the photometric optical system of one embodiment of the present invention shown in the figure when viewed from the rear of the pentaprism, and FIG. 9 is an explanatory diagram of the conventional photometric optical system viewed from the rear of the pentaprism.
FIG. 0, FIG. 13, and FIG. 16 are optical path diagrams showing the image formation state of a point on the upper part of the photographing screen of the condenser lens in one embodiment of the present invention, and FIG.
4, FIG. 17 is an optical path diagram showing an image forming state of a point in the central portion of the photographing screen of the condenser lens in one embodiment of the present invention, respectively, 12, 15, 15
FIG. 18 is an optical path diagram showing an image forming state of a point under a photographing screen of a condenser lens in one embodiment of the present invention, and FIGS. 19 and 20 are photometric optical systems in other embodiments of the present invention. FIG. 21 is an explanatory view when seen from the rear of the pentaprism, and FIG. 21 is a schematic view of an optical system of a single-lens reflex camera showing another embodiment of the present invention.
FIG. 22 is an optical path diagram showing an image forming state of a point on an upper portion of a photographing screen of a condenser lens according to another embodiment of the present invention, and FIG. 23 is a photographing screen of a condenser lens according to another embodiment of the present invention. FIG. 24 is an optical path diagram showing the image forming state of the central portion, and FIG. 24 is an optical path diagram showing the image forming state of the lower part of the photographing screen of the condenser lens in another embodiment of the present invention. In the figure, 1 is a photographing lens, 2 is a QR mirror, 3 is a focusing screen, and 4
Is a penta prism, 5 is an eyepiece lens, 6,19,19 ', 20,2
0'is a condenser lens according to the present invention, 12, 13, 15, 17 are conventional condenser lenses, 7 is a light receiving means, 8 is a film surface, 9 is an optical axis of a photographing lens, 10 is an optical axis of a finder, 11 Is the optical axis of the photometric system,
Reference numeral 18 is an effective portion of the finder, reference numerals 30 and 40 are portions obtained by removing a part of the condenser lens, and reference numerals 31 and 41 are light rays removed when the condenser lens is removed.

Claims (1)

[Claims] 1. A light beam other than an effective light beam for observing a finder image, which has passed through the prism, is received by using a condenser lens and a light receiving means arranged behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera that measures the object field by cutting out at least a part of the finder optical axis side of the condenser lens, the cutout portion of the condenser lens provides a light beam for finder image observation. The photometric optical system of a single-lens reflex camera, which is placed close to the optical axis of the viewfinder without obstructing it.