JPS5983133A - Focusing display device of single lens reflex camera - Google Patents

Abstract

PURPOSE:To enable the titled device to display a focusing signal within the visual field of a finder without adding newly an optical system to a camera by utilizing a half-mirror for splitting a luminous flux for detecting focusing from a luminous flux for imaging. CONSTITUTION:A part of a luminous flux for imaging past a photographic objective lens 1 is split by a half-mirror 3 and is projected as a luminous flux for detecting focusing on a focusing detecting element 4. The detection signal is fed to a light emitting element 10 for a focusing signal and the luminous flux of the focusing signal is reflected successively by the mirror 3 and a quick return mirror 5 while it is condensed by an imaging optical system 11, until it is imaged on a finder screen 7. The optical system for displaying the focusing signal is so disposed that the luminous flux for detecting focusing is imaged at the part of the screen 7 except the focusing detection part 7a thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a focus display device for a single-lens reflex camera that displays information within the field of view.

In conventional focus display devices of this kind, the optical system for guiding the focus signal beam emitted from the light emitting element onto the finder screen was completely separate from other optical systems, resulting in a complex configuration and high cost. There was a problem with becoming.

In view of the above problems, the present invention provides a light splitting prism equipped with a no-f mirror for splitting a light beam for focus detection from a light beam for imaging, and a light splitting prism that emits light when in focus to display a focus signal. and an imaging optical system that reflects the focus signal light beam from the focus signal light emitting element on the nof mirror and forms an image on the finder screen. In particular, it is an object of the present invention to provide a focus display device that can display a focus signal within the viewfinder field of view without adding a new optical system for guiding the focus signal light beam onto the finder screen. This will be explained based on one embodiment shown below. 1 is a photographic objective lens, 2 is a light splitting prism equipped with a nof mirror 3 for splitting a light beam for focus detection from a light beam for imaging. , 4 is a focus detection element which is disposed at the same distance as the finder screen to be described later regarding the no-f mirror 3 and onto which a focus detection light beam is projected; 5 is a flip-up mirror; 6
7 is a film that is placed at the same distance as the finder screen, which will be described later, regarding the flip-up mirror 5, and onto which a beam of light for imaging is projected when the flip-up mirror 5 is flipped up. When the position (lowered position) is lowered, the viewfinder lens 8 projects the light beam reflected by the flip-up mirror 5 for image formation, 8 is a pentaprism, 9 is an eyepiece lens, and 10 is a focus detection element 4. A focus signal light emitting element 11 emits light in response to a detection signal to display a focus signal when focus is detected, and reference numeral 11 directs the focus signal light beam from the focus signal light emitting element 1o to a half mirror 3 and a flip-up mirror 5. This is an imaging optical system that sequentially reflects the light and forms an image on the finder screen 7.

Since the focus display device according to the present invention is constructed as described above, a part of the light beam for imaging passing through the photographic objective lens 1 is divided by the half mirror 3 and becomes a light beam for focus detection as shown in FIG. The image is projected onto the focus detection element 4 as shown in (a). In this case, the portion A where the light beam for focus detection is in focus (the portion projected onto the light receiving surface of the focus detection element 4)
- Portion B that is transmitted through half mirror 3 corresponding to A' -
``B'' is projected onto the focus detection section 7a on the finder screen 7 as shown in FIG. 2(b).

When focus is detected, a detection signal is sent from the focus detection element 4 to the focus signal light emitting element 10, so that the light emitting element emits light to display the focus signal. The focusing signal light beam is condensed by the imaging optical system 11 and sequentially reflected by the half mirror 3 and flip-up mirror 5, and is then imaged onto the finder screen 7. At this time, as shown in FIG. 3, a part of the focus signal light beam passes through the half mirror 3 and proceeds in the direction of the focus detection element 4, and is focused on the finder screen as the focus signal light beam a. When an image is formed on the detection unit 7a, a part of it passes through the half mirror 3 and then enters the focus detection element 4, so stable focus detection cannot be performed. When the image is formed on a portion other than the upper focus detection section 7a, the portion transmitted through the half mirror 3 does not enter the focus detection element 4, so that stable focus detection can be performed. Therefore, it is desirable to arrange the focus signal display optical system so that the focus detection light beam forms an image on a portion of the finder screen 7 other than the focus detection section 7a. After a while, the focus signal is displayed within the field of view of the finder, but the present focus display device does not need to add a new optical system for guiding the focus signal beam onto the finder screen 7, so the configuration is simple. is simple and manufacturing costs are low.

As described above, the focus display device according to the present invention has the important practical advantage of being simple in structure and low in manufacturing cost.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system of an embodiment of a focus display device according to the present invention, and FIG. 2 is a diagram showing a projection state of a focus detection portion of a focus detection light beam and a corresponding transparent portion in the above embodiment. 3 are diagrams showing the imaging state of the focusing signal light beam in the above embodiment. 2...Light splitting prism, 3...Half mirror 14.
-Focus detection element, 5... flip-up mirror, 7... finder screen, 10... focus signal light emitting element, 11
...Imaging optical system. Agent Yasushi Shinohara a) b) Figure 3

Claims (1)

[Claims] A light splitting prism equipped with a half mirror for splitting a light beam for focus detection from a total light beam for imaging, a focus signal light emitting element capable of emitting light and displaying a focus signal when in focus, and A focus display device for a single-lens reflex camera comprising an imaging optical system that reflects all of the focused signal light flux from a signal light emitting element on the above-mentioned half mirror and then forms an image on a finder screen.