Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-06-08
2002-02-12
Font, Frank G. (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C256S013000, C396S121000, C396S114000, C396S104000
Reexamination Certificate
active
06346694
ABSTRACT:
This application is based on Application No. HEI 10-160278 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focus detecting device for use in cameras and the like, and specifically relates to a focus detecting device capable of large amount of defocus.
2. Description of the Related Art
The phase difference detecting method is representative of conventional focus detecting methods used in cameras and the like. The phase difference detecting method is the method typically used in modern single-lens reflex cameras. The phase difference detecting method determines the focus state via the relative divergence of a secondary image formed by a separator lens comprising a pair of relay lenses arranged behind a film equivalent plane.
FIG. 11
is a perspective view of a conventional autofocus module using the phase difference detecting method. In the drawing, reference number
51
refers to a filter for cutting the infrared component. Reference number
52
refers to a condenser lens. Reference number
53
refers to a mirror. Reference number
54
refers to a an aperture mask. Reference number
55
refers to a separator lens. Reference number
56
refers to a charge-coupled device (CCD) sensor.
As shown in the drawing, the filter
51
cuts the infrared component of the photographic light
50
passing through a taking lens (not shown in the drawing) and forming an image in the vicinity of the film equivalent plane. Furthermore, the light is divided into a pair of luminous fluxes in the on-axis and extra-axis focus areas of the optical axis X by the condenser lens
52
and the aperture mask
54
between which the mirror
53
is interposed. The luminous flux again forms an object image in two areas (standard area and reference area) on the CCD sensor
56
provided in correspondence to a pair of lenses via the separator lens
55
.
The re-formed object image has a narrow image interval in the front focus state and a wide image interval in the rear focus state compared to the in-focus state. The focus position is detected by detecting the image interval of the object image on the CCD sensor
56
.
However, the focus detecting range in the phase difference detecting method is generally approximately ±10 mm. When the focus detection range is wider than approximately ±10 mm, the distance is increased from the so-called film equivalent plane to the surface of the CCD sensor
56
, thus increasing the size of the device. Furthermore, the depth of focus must be ensured to have a focal point at which the secondary image on the surface of the CCD sensor
56
corresponds to a broad focus detecting range. For this reason, a F-number value of the separator lens
55
comprising a relay lens system must be used to produce darkening, thus making use difficult in the low luminance range.
The taking lens which is a weak point of the focus detecting device using the phase difference detecting method is the macro lens. Since this lens has a high photographic magnification of near objects, large movement of focusing (amount of defocus), and an excessively large focus range on a single view of the focus detecting device, the taking lens must be driven to a position at which focus detection is possible. Under low contrast conditions, for example, a slow lens drive control is executed to drive the lens to a position at which focus detection can be achieved (hereinafter referred to as “low contrast scan”).
In this instance, since the focus direction is unclear, the operation may move the lens to the end in the direction opposite the focus direction and returning the lens in the focus direction. Since the macro lens has a large amount of extension, time is required to drive the lens, thereby producing a large time loss to attain focus. These disadvantages are similarly present in telephoto lenses. This tendency is particularly pronounced when a telephoto macro lens is used, thus adversely affecting the autofocus operation characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a focus detecting device capable of detecting the focus direction and correspondingly capable even in the case of a large defocus which cannot be detected by a conventional focus detection device. These objects are attained by the present invention comprising an optical system which forms an image of a photographic subject, a first sensor pair having a first image sensor and a second image sensor which receives light flux from said subject through said optical system, a second sensor pair having a third image sensor and a forth image sensor which receives light flux from said subject through said optical system, a first focus detector which detects a focus condition of said optical system based on outputs of said first sensor pair, a second focus detector which detects a focus condition of said optical system based on outputs of said second sensor pair, and a third focus detector which detects a focus condition of said optical system based on outputs of said first image sensor and said third image sensor.
One image sensor among the first sensor pair and one image sensor among the second sensor pair are arranged at symmetrical positions relative to the optical axis.
A focus correcting lens is inserted directly anterior to one image sensor among the first sensor pair and one image sensor among the second sensor pair, respectively.
This construction provides a focus detecting device capable of detecting the focus direction and correspondingly capable even in the case of a large defocus which cannot be detected by a conventional focus detection device.
REFERENCES:
patent: 5003336 (1991-03-01), Karasaki et al.
patent: 5530513 (1996-06-01), Ohsawa
patent: 5539493 (1996-07-01), Kusaka
patent: 5870635 (1999-02-01), Shindo et al.
Hamada Masataka
Kimba Akio
Ueda Hiroshi
Burns Doane , Swecker, Mathis LLP
Font Frank G.
Minolta Co. , Ltd.
Smith Zandra
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