Focus Control Device Dynamic Detection Interval Adjustment
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Solution Overview
Problem
In autofocus control using the contrast mode, the irregular change in contrast for each detection interval due to focus sensitivity and other factors complicates the accurate detection of the in-focus position, especially when the detection interval is large, leading to difficulties in interpolation calculations and achieving a desirable in-focus state.
Innovation Solution
A focus control device that calculates the number of in-detection-range focal depths based on the detection range and determines the detection interval using these focal depths, ensuring a constant amount of contrast change for each interval, thereby improving the accuracy of in-focus position detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the detection interval is increased, then the time necessary to detect the entire detection range decreases, but the accuracy in detection of the position at which the contrast becomes the maximum becomes low
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the detection interval based on the current focus lens position and calculated focal depth. When the focus lens is at a position with large focal depth, a larger detection interval is used to reduce detection time. When the focus lens is at a position with small focal depth, a smaller detection interval is used to improve detection accuracy. This dynamic parameter adjustment resolves the contradiction between detection speed and accuracy.
2Measurement precision
If the detection interval is decreased, then the accuracy in detection of the position at which the contrast becomes the maximum becomes high, but the time necessary to detect the entire detection range increases
Solution Approach 1:
The patent implements parameter changes by setting the detection interval according to the calculated focal depth at each detection position. The detection interval is not fixed but varies based on the optical characteristics at different positions. This allows the system to achieve high accuracy where needed (small focal depth) while maintaining fast detection where possible (large focal depth).
3Device complexity
If the amount of shift of the focus lens corresponding to the detection interval is set to be constant, then the detection process is simplified, but the amount of change in the contrast of the image for each detection interval is irregularly changed by the effects of focus sensitivity, making it difficult to perform interpolation calculation at high accuracy
Solution Approach 1:
The patent resolves this contradiction by changing the detection interval parameter based on the calculated focal depth. By adjusting the detection interval to correspond to the actual optical characteristics at each position, the system ensures that the contrast change amount remains relatively consistent across detection intervals. This enables accurate interpolation calculation while maintaining manageable process complexity.
Data Source
AI summary
A focus control device includes: an in-detection-range focal depth number calculation section that calculates the number of in-detection-range focal depths as the number of focal depths, which are divided as division units and each of which depends on a position of a focus lens, in accordance with a detection range in which the focus lens is shifted in order to detect the contrast of a captured image signal; a detection interval determination section that determines the number of in-detection-interval focal depths, which represents the number of focal depths as the division units, as a detection interval in the detection range, in accordance with the calculated number of in-detection-range focal depths; and a focus lens shift instruction section that instructs a lens section to perform a focus search which shifts the focus lens by specifying the detection range and the number of in-detection-interval focal depths determined as the detection interval.