Automatic focusing apparatus having a variable focusing speed an

Details Automatic focusing apparatus having a variable focusing speed an Automatic focusing apparatus having a variable focusing speed an

1988-06-24

1990-05-01

Groody, James J.

Facsimile and static presentation processing

Facsimile

Recording apparatus

358228, H04N 5232

Patent

active

049223461

ABSTRACT:
In an automatic focusing apparatus of a video camera, a first focus evaluating value which steeply changes and a second focus evaluating value which gently changes relative to the position of a lens, are detected in response to a video signal obtained in an image sensing circuit (4). A switching circuit (19) alternately selects the first and second focus evaluating values every one field to apply the same to in-focus state detecting circuits (20, 21), respectively. The in-focus state detecting circuits (20, 21), together with a focusing motor control circuit (10), perform an automatic focusing operation by hill-climbing control. In addition, a calculating circuit (22) calculates the relative ratio of the first focus evaluating value to the second focus evaluating value. The focusing motor control circuit (10) sets the rotational speed of a focusing motor (3) to a normal speed when the calculated relative ratio is smaller than a predetermined value while setting the rotational speed of the focusing motor (3) to a low speed when it is larger than the predetermined value. Therefore, a lens (1) is moved at low speed when the focusing lens is in the vicinity of the in-focus position while being moved at high speed when it is in the defocused state.

REFERENCES:
patent: 4531158 (1985-07-01), Murakami et al.
patent: 4614975 (1986-09-01), Kaite
patent: 4638364 (1987-01-01), Hiramatu

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