Multi-zone autofocus system for a still camera

Details Multi-zone autofocus system for a still camera Multi-zone autofocus system for a still camera

1999-10-01

2001-08-14

Adams, Russell (Department: 2851)

Photography

With exposure objective focusing means, focusing aid, or...

Plural focusing or rangefinding areas

C396S103000, C396S106000

Reexamination Certificate

active

06275658

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the field of autofocus systems for still cameras and more specifically to a low cost system utilizing a limited zone autoranging device to establish an object focus distance setting in an expanded number of focus zones.
BACKGROUND OF THE INVENTION
It is common in more expensive still cameras to employ an autofocus system which utilizes an autoranging system to determine the distance of an object in a scene to be captured and to actuate lens focusing apparatus to move the lens to an exact focus position that corresponds to the determined distance. In less expensive cameras, the autofocus apparatus is adapted to move the lens to one of a limited number of focus positions that corresponds to selected distance zones away from the camera. For example, a two zone focus camera employs an autofocus apparatus coupled with a two zone autoranging device that will set the taking lens focus position at either a “far” or “near” position depending on whether the ranging device finds the principal object in the scene to be beyond or closer than a predefined intermediate distance, typically 6 feet, that separates the two zones. By setting the focus at a suitable distance point within the zone indicated by the ranging device, appropriate shutter aperture and speed settings then establish an adequate depth-of-field to assure acceptable focus throughout most of the zone involved.
While two zone cameras are commonly accepted, there are occasions when it is desirable to distinguish between a “near” distance zone typically used for group shots and a closer distance zone, such as 2-3 feet, typically used for closeup shots of individuals. In this case, the camera conventionally employs a three zone autofocus apparatus coupled with a three zone autoranging device, the latter outputting a “far”, “near” or “closeup” indication to the autofocus apparatus to set the appropriate taking lens focus position. The use of a three zone autoranging device requires a more expensive integrated circuit and light source to implement as compared to a two zone device. Consequently, there is a need in low cost cameras for a less costly arrangement and, more specifically, to employ a two zone autoranging device in a manner that enables setting a three zone autofocus apparatus to an appropriate distance setting that includes a “closeup” setting as well as “far” and “near”.
SUMMARY OF THE INVENTION
In accordance with the invention, therefore, there is provided a multi-zone autofocus system for a still camera that comprises a distance threshold setting circuit sequentially changeable to set first and second threshold values corresponding to a first distance from the camera and to a second, closer, distance from the camera; a two zone autoranging circuit connected to said threshold setting circuit and operable to locate an object in one of two distance zones separated by a distance determined by a value of said threshold setting circuit; and autofocus apparatus responsive to said autoranging circuit for setting a camera focus to one of at least two distance zones determined by said autoranging circuit. The system further includes a camera controller programmed to activate said autoranging circuit to perform a first autoranging operation with said distance threshold setting circuit set to said first threshold value to determine if said object is located in a zone nearer or farther than said first distance amount and, if farther, to activate said autofocus apparatus to set camera focus for a first distance zone farther than said first distance and, if nearer, to activate said autoranging circuit to perform a second autoranging operation with said distance threshold setting circuit set to said second threshold value to determine if said object is located in a zone nearer or farther than said second distance and, if farther, to activate said autofocus apparatus to set camera focus for a second distance zone between said first and second distances and, if nearer, to set said autofocus apparatus for a third distance zone closer than said second distance.
In a preferred form of the invention, the threshold setting circuit comprises first and second resistors and a switch, such as a switching transistor, connected in circuit with the second transistor. The first resistor establishes the threshold for the first autoranging operation and, when required depending on the outcome of the first autoranging operation, the controller sets the switch to couple the second resistor in parallel with the first resistor thereby setting the second threshold for the second autoranging operation to distinguish between near and closeup zones.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.


REFERENCES:
patent: 3375460 (1968-03-01), Miller
patent: 4238153 (1980-12-01), Imura
patent: 4300824 (1981-11-01), Tokuda et al.
patent: 4518253 (1985-05-01), Takahashi
patent: 4615599 (1986-10-01), Kataoka et al.
patent: 5138358 (1992-08-01), Aoyama et al.
patent: 61203429A (1996-09-01), None

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