Camera Focus Adjusting System with Limited Search Range
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Solution Overview
Problem
Conventional digital cameras with contrast-detection type focus adjusting systems often require excessive time for AF search operations, especially when refocusing after an initial in-focus state is achieved, as they move the focusing lens group across the entire range even if the main object remains unchanged.
Innovation Solution
The camera employs a focus adjusting system that narrows the controllable searching range to a limited area around the current focusing lens group position after an in-focus state is achieved, using image comparison and stepwise movement to quickly determine if the object is still in focus, thereby reducing unnecessary search operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the AF search operation moves the focusing lens group from one extremity to the other of the entire range, then the in-focus position can be reliably detected, but the time required for the AF search operation increases significantly
Solution Approach 1:
The patent divides the entire focusing range into multiple sub-ranges and performs AF search operations sequentially in each sub-range rather than sweeping across the entire range. This segmentation allows the system to maintain reliable in-focus detection while significantly reducing the time required by stopping the search once the in-focus position is found within each sub-range.
Solution Approach 2:
The patent performs preliminary actions by capturing images at multiple focal positions within each sub-range before determining the in-focus position. This preliminary image capture and comparison allows the system to quickly identify when the in-focus state is achieved without needing to sweep through the entire focusing range, thereby reducing overall AF search time while maintaining detection reliability.
2Reliability
If the AF search operation is performed again after an in-focus state is achieved, then the focusing accuracy is maintained, but the time required for refocusing increases when the main object remains unchanged
Solution Approach 1:
The patent performs preliminary actions by capturing an image at the in-focus position before the refocusing operation and storing it in memory. When refocusing is needed, the system compares the newly captured image with the stored preliminary image to determine if the main object remains unchanged. This preliminary image capture enables quick refocusing by avoiding unnecessary full-range AF search operations when the object remains the same.
Solution Approach 2:
The patent implements feedback by comparing the newly captured image with the stored preliminary image and using this comparison result to determine whether to perform a full-range AF search or a limited-range search. This feedback mechanism allows the system to maintain focusing accuracy while reducing refocusing time by adapting the search range based on whether the main object has changed.
3Speed
If the focusing lens group is moved stepwise within a limited searching range, then the refocusing speed is improved, but the measurement precision of the in-focus position may be reduced
Solution Approach 1:
The patent segments the focusing range into multiple sub-ranges and performs stepwise movement within each sub-range. This segmentation allows the system to maintain measurement precision within each localized sub-range while achieving faster refocusing speeds overall, as the system doesn't need to sweep through the entire range when refocusing after an in-focus state is achieved.
Solution Approach 2:
The patent applies partial action by performing AF search operations only within the necessary limited searching range rather than the full range. This partial action is sufficient to maintain measurement precision for the current focusing condition while significantly improving refocusing speed by avoiding unnecessary movements outside the relevant range.
Data Source
AI summary
A camera with a photographing optical system, including a focus adjusting system which captures images at different focal positions via an image pickup device while moving a focusing lens group within a controllable searching range, and moves the focusing lens group to the in-focus position; a memory which stores a first image captured when an in-focus state is achieved; and a comparing device which compares the first image stored in the memory with a second image captured via the image pickup device before commencement of movement of the focusing lens group. The focus adjusting system operates within a limited searching range including a current position of the focusing lens group when predetermined conditions are satisfied, including a condition upon which it is determined that the first image and the second image match each other completely or by a predetermined degree.