Zoom Lens Control Apparatus for Autofocus Stability
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Solution Overview
Problem
Existing zoom lens control systems experience increased focus fluctuations and control deviations during zoom tracking, particularly when the focus lens is driven by autofocus (AF) during continuous zooming, leading to potential capture of out-of-focus images.
Innovation Solution
A control apparatus that acquires information on the position of the magnification varying lens and the object distance, calculates a target position for the focus lens using control information, and controls the driving of the focus lens to reduce focus fluctuations and control deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the focus lens is driven by AF during zoom tracking, then autofocus accuracy is improved, but control deviation increases due to sudden acceleration or deceleration
Solution Approach 1:
The control apparatus calculates a predicted focus lens position based on current zoom position and zoom speed before AF driving occurs. This predicted position serves as a reference to pre-adjust the zoom speed command, preventing sudden acceleration or deceleration when AF starts. By performing this prediction and pre-adjustment in advance, the system maintains control stability while allowing AF to achieve accurate focus.
Solution Approach 2:
The control apparatus continuously monitors the actual focus lens position and compares it with the predicted position. Based on this feedback, the system dynamically adjusts the zoom speed command to minimize deviation between actual and predicted positions. This closed-loop feedback mechanism ensures that AF operations do not cause excessive control deviation, maintaining both autofocus accuracy and control stability.
2Stability of the object's composition
If zoom tracking is performed during continuous zooming, then focus fluctuations are reduced, but reverse drive occurs when AF drive direction opposes zoom tracking direction
Solution Approach 1:
The control apparatus dynamically determines the zoom speed command based on the relationship between AF drive direction and zoom tracking direction. When directions oppose, the system adjusts zoom speed to prevent reverse drive; when directions align, normal zoom tracking proceeds. This dynamic adaptation maintains focus stability while managing control complexity through conditional logic rather than fixed control rules.
Solution Approach 2:
The predicted focus lens position acts as an intermediary between zoom tracking control and AF control. By comparing the actual position with this predicted intermediate value, the system can detect potential reverse drive conditions and adjust zoom speed accordingly. This intermediary mechanism resolves the conflict between maintaining focus stability during zoom tracking and preventing reverse drive when AF operates in opposite direction.
3Speed
If the focus lens accelerates or decelerates suddenly when AF starts during zoom tracking, then autofocus response speed is improved, but control delay increases
Solution Approach 1:
The control apparatus performs preliminary calculation of the predicted focus lens position based on current zoom parameters before AF driving begins. This prediction allows the system to pre-adjust the zoom speed command, so when AF starts, the focus lens is already positioned to minimize travel distance. This preliminary positioning maintains fast AF response while reducing control delay by avoiding sudden large movements.
Solution Approach 2:
The control apparatus changes the zoom speed parameter dynamically based on AF operation status. When AF is detected, the system modifies the zoom speed command to accommodate AF driving, preventing excessive acceleration or deceleration. This parameter adjustment maintains reasonable AF response speed while reducing control delay by smoothing the transition between zoom tracking and AF modes.
Data Source
AI summary
A control apparatus for reducing focus fluctuation of a zoom lens including a focus lens and a magnification varying lens includes a processor configured to acquire, at a first time, information on a position of the magnification varying lens for a second time after the first time and information on an object distance for the second time, acquire a first target position according to the position of the magnification varying lens at the second time and the object distance at the second time, using control information on the position of a magnification varying lens and a position of the focus lens according to the object distance, and control driving of the focus lens using control information and the first target position.