Focus Lens Speed Control for Stable Autofocus
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Solution Overview
Problem
Existing autofocus systems struggle to maintain focus stability when subject distances change significantly, leading to variations in focus lens position and degraded image quality.
Innovation Solution
A focus control device that adjusts the movement speed of the focus lens based on the difference between the current position and the estimated focusing position, using phase-difference detection pixels to determine when to increase or decrease speed, and stop movement when the difference falls within certain threshold values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the focus lens moves at a constant high speed during autofocus, then the focusing response is fast, but the focus lens position varies excessively when subject distance changes significantly
Solution Approach 1:
The patent applies dynamics by making the focus lens moving speed variable rather than constant. The control unit dynamically adjusts the moving speed based on the absolute value of the difference between current position and estimated focusing position. When the difference is large, higher speed is used for fast response; when the difference becomes small, speed is reduced to prevent overshooting and maintain stability. This dynamic speed adjustment resolves the contradiction between fast focusing response and focus position stability.
2Loss of time
If the focus lens moves quickly to reach the estimated focusing position, then the autofocus time is reduced, but the phase-difference detection accuracy decreases when the subject distance changes greatly
Solution Approach 1:
The patent implements feedback control by continuously monitoring the absolute value of the difference between the current focus lens position and the estimated focusing position. The control unit uses this feedback information to dynamically adjust the moving speed. When the difference exceeds a threshold (indicating large subject distance change and reduced detection accuracy), the system allows faster movement. When the difference is within the threshold (indicating accurate detection), the system reduces speed for precision. This feedback mechanism balances autofocus speed with phase-difference detection accuracy.
Data Source
AI summary
A focus adjustment unit acquires a current position of a focus lens on an optical axis by deriving the current position based on a drive amount. A focus derivation unit acquires an estimated focusing position. A speed setting unit sets a moving speed to a first speed in a case in which an absolute value of a difference between the current position and the estimated focusing position is less than a threshold value. A focus lens drive controller moves the focus lens at the first speed. The speed setting unit sets the moving speed to a second speed lower than the first speed in a case in which the absolute value of the difference between the current position and the estimated focusing position is equal to or greater than the threshold value. The focus lens drive controller moves the focus lens at the second speed.