Imaging Device Autofocus Breathing Compensation via F-Number Limiting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In imaging devices with lenses that exhibit 'breathing' (change in image magnification with focus lens position), autofocus accuracy decreases when the image magnification change is not considered during autofocus evaluation.
Innovation Solution
An imaging device that acquires reference values for image magnification changes with focus lens position, derives corresponding changes in the autofocus area, determines a limit F-number based on a threshold value, and adjusts the F-number for exposure to prevent subject misalignment within the autofocus area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If autofocus is executed using evaluation value in autofocus area without considering image magnification change, then autofocus operation is simple, but focusing accuracy decreases
Solution Approach 1:
The system pre-acquires reference values for image magnification changes at different focus lens positions before executing autofocus. This preliminary data collection enables the subsequent autofocus process to compensate for breathing effects without adding operational complexity, thereby maintaining ease of operation while improving focusing accuracy.
Solution Approach 2:
The patent introduces an intermediary parameter (image magnification change amount) that mediates between the focus lens position and the autofocus evaluation. By deriving this intermediate value and using it to correct the autofocus area or evaluation values, the system resolves the contradiction between simple operation and accurate focusing.
2Measurement precision
If limit F-number is determined based on image magnification change, then focusing accuracy is maintained, but device complexity increases
Solution Approach 1:
The system changes the F-number parameter dynamically based on the derived image magnification change amount. By establishing a relationship between magnification change and acceptable F-number limits, the system maintains focusing accuracy through parameter adjustment without requiring complex hardware modifications, thus managing device complexity effectively.
3Measurement precision
If F-number is adjusted to maintain focus accuracy, then focusing precision is improved, but exposure control complexity increases
Solution Approach 1:
The patent merges the autofocus control and exposure control functions by integrating the image magnification change consideration into a unified F-number determination process. The setting unit simultaneously manages both focusing and exposure parameters based on the derived magnification change, reducing overall system complexity despite the increased precision requirements.
Data Source
AI summary
An imaging device derives a change amount of image magnification corresponding to each of a plurality of F-numbers in an autofocus area on the basis of a reference value of the change amount of the image magnification in accordance with a change in position of a focus lens for each of the plurality of F-numbers, in a case where autofocus is executed; determines, as a limit F-number, an F-number corresponding to any change amount equal to or less than a threshold value of the allowed change amount of the image magnification among the derived change amounts; and sets an F-number as the limit F-number in a case where the F-number obtained from a subject luminance in a case where autofocus is executed exceeds the determined limit F-number.