Auto-focus system and auto-focus method thereof

Details Auto-focus system and auto-focus method thereof Auto-focus system and auto-focus method thereof

2008-12-30

2010-12-07

Laballe, Clayton E (Department: 2862)

Photography

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

Having auxiliary illumination

C396S157000

Reexamination Certificate

active

07848629

ABSTRACT:
An exemplary auto-focus method includes the following steps. An ambient brightness is measured before a pre-flash. Then, a pre-flash ambient brightness is also measured during the pre-flash is fired. A main flash ratio is subsequently calculated using the ambient brightness, the pre-flash ambient brightness, and a preset desired brightness. Next, an object distance is indexed using the calculated main flash ratio and a table. The table includes a collection of main flash ratios and a collection of object distances, where each flash ratio is associated with a corresponding object distance. Then an image distance corresponding to the indexed object distance is calculated using the imaging formula. The calculated image distance is converted into a number of focus steps of a focus lens. Finally, the focus lens is moved with a corresponding number of focus steps.

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