Focus detecting device

• US 4,384,770 A
• Filed: 06/29/1981
• Issued: 05/24/1983
• Est. Priority Date: 05/17/1978
• Status: Expired due to Term

• Current Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Nakamura, Kazuo, Ogawa, Ryota, Ohishi, Michiro, Tokutomi, Seijiro, Tachihara, Satoru, Jyojiki, Masao
• Primary Examiner(s): Gonzales, John
• Application Number:
  US06/278,030
• Time in Patent Office: 694 Days
• Field of Search: 354/25, 350/171, 350/296
• US Class Current: 396/111
• CPC Class Codes: G02B 7/34 using different areas in a pupil plane

Abstract

A focus detecting device having two concave mirrors for reforming the image of an object which is formed between a lens and the focal plane of lens, and for dividing said image two same secondary images. Two light receiving element arrays are provided in the image forming planes of the secondary images. A signal processing circuit subjects the outputs of the light receiving element arrays to produce a signal indicating whether or not the lens is focussed on the object. By means of the two concave mirrors adapted to form said secondary images, the two secondary images are shifted in the opposite directions on the light receiving element arrays at the time of defocussing so that the difference between the outputs of the two light receiving element arrays is not zero. At the time of proper focus the two secondary images are located at equivalent positions on said light receiving element arrays so that the difference between the outputs of the two light receiving element arrays is zero. A signal processing circuit produces a signal indicating the establishment of the proper focus.

Claims

1. A focus detecting device for a single lens reflex camera having a movable mirror comprising:

a pair of concave mirrors formed as divided components from a unitary concave mirror surface, said concave mirrors reforming a primary image of an object which is formed between a lens and the focal plane of said lens;

deflection means on said mirror for directing said primary image onto said concave mirrors;

said concave mirrors dividing the primary image into two secondary images;

a pair of light receiving element arrays provided in the image forming planes of said secondary images and receiving said secondary images from said concave mirrors;

means to shield said light receiving element arrays from the focal plane of said lens, signal processing circuit means for subjecting the outputs of said light receiving element arrays to comparison and producing an output signal indicating whether or not said lens is focussed on said object, said signal processing circuit means comprising differential circuit means responsive to the outputs of a corresponding pair of elements in said pair of light receiving element arrays, absolute value circuit means for converting the output of said differential circuit means into an absolute value signal, transducer means to convert the extension of said lens into an electrical signal and detector means receiving said electrical signal and said absolute value signal and producing said output signal, wherein said two secondary images are shifted in the opposite direction on said light receiving element arrays if the image is defocussed so that the difference between the outputs of said two light receiving element arrays is not zero, and when the image is focussed said two secondary images are located at equivalent positions on said light receiving element arrays so that the difference between the outputs of said two light receiving element arrays is zero, and display means receiving the output signal from said signal processing circuit means for indicating the state of focus.

2. A focus detecting device of claim 1 wherein said concave mirrors are ellipsoidal mirrors.

3. A focus detecting device of claim 1 wherein said concave mirrors are spherical mirrors.

4. The device of claim 1 wherein said detector means produces said output signal as a function of minimum absolute value with respect to lens extension.

5. The device of claim 1 wherein said light receiving arrays respectively comprise a series of N light sensitive elements.

6. The device of claim 5 wherein said differential circuit means comprises a series of N differential circuits said absolute value circuit means comprises N absolute value detectors coupled respectively to said differential circuit and further comprising an addition circuit for adding the outputs of said absolute value detectors and supplying said absolute value signal to said detector means.

7. The device of claim 5 wherein said light sensitive elements are silicon photo-diodes.

8. The device of claim 5 wherein said light sensitive elements are chemical semiconductors.

9. The device of claim 5 wherein said light sensitive elements are charge coupled devices.

10. The device of claim 5 wherein said light sensitive elements are self-scanning type image sensors.

11. The device of claims 1, 2, or 3 wherein said lens comprises of photography lens on a camera.

12. The device of claim 11 further comprising a mirror means receiving the primary image and deflecting said image to said concave mirrors which allows viewing of said image in a view finder of said camera.

13. The device of claim 12 further comprising an aperture positioned between said mirror means and said concave mirrors.