Autofocus Micro-Adjustment via Contrast-Defocus Function
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Solution Overview
Problem
Conventional image pickup apparatuses, especially single-lens reflex cameras, suffer from significant autofocus errors due to manufacturing defects and user-dependent calibration inaccuracies, leading to focus errors larger than permissible values.
Innovation Solution
An image pickup apparatus with a control system that calculates defocus amounts using phase difference focus detection and contrast evaluation values, determining an adjusting value based on an extreme value of a function indicating the relationship between defocus and contrast values at multiple lens positions, enabling precise micro-adjustment of autofocus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional AF function is used, then basic focusing is achieved, but focus error exceeds permissible value due to manufacturing errors
Solution Approach 1:
The system captures multiple images at different lens positions, calculates contrast evaluation values for each, and uses this feedback information to determine the optimal lens position. This closed-loop feedback mechanism compensates for manufacturing errors in both the camera body and lens by automatically adjusting based on actual image quality measurement.
Solution Approach 2:
The patent replaces manual user adjustment of focus with an automated computational system that uses contrast evaluation algorithms. The micro adjusting unit automatically calculates and applies the optimal lens position based on contrast measurements, substituting mechanical manual adjustment with computational optimization.
2Ease of operation
If user manually selects reference defocus amount, then calibration is performed, but selection accuracy scatters and user burden increases
Solution Approach 1:
The system performs calibration automatically without requiring user intervention for selecting reference defocus amounts. The micro adjusting unit autonomously captures multiple images, calculates contrast evaluation values, determines the optimal lens position, and applies the correcting value. This self-service mechanism eliminates user burden and ensures consistent, scatter-free calibration results.
Solution Approach 2:
The patent introduces a contrast evaluation calculation unit as an intermediary between the lens positioning system and the final focus adjustment. This intermediary objectively measures image quality through contrast evaluation, replacing subjective user judgment with a quantifiable metric that eliminates scattering in selection accuracy.
3Manufacturing precision
If multiple images are captured for calibration, then defocus correction is possible, but lens driving amount scatters and calibration becomes unstable
Solution Approach 1:
The system changes the evaluation parameter from subjective user selection to objective contrast evaluation values. By capturing multiple images at different lens positions and calculating contrast metrics for each, the system identifies the optimal position through quantitative comparison. This parameter change stabilizes calibration by using a consistent, objective metric rather than variable user judgment.
Solution Approach 2:
The patent performs preliminary capture of multiple images at different lens positions before determining the final optimal position. This preliminary action of capturing a series of images with varying lens driving amounts allows the system to pre-establish the contrast-evaluation-versus-position relationship, from which the optimal position is subsequently derived through calculation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides highly accurate autofocus adjustments by automating the process, reducing user burden and eliminating errors associated with manual calibration and lens manufacturing defects, ensuring focus accuracy within permissible limits.
Implementation Method 1
a first calculating unit configured to calculate a defocus amount by a focus detection of a phase difference method
Implementation Method 2
a second calculating unit configured to calculate a contrast evaluation value of an image
Data Source
AI summary
A control apparatus includes a first calculating unit configured to calculate a defocus amount by a focus detection of a phase difference method, a second calculating unit configured to calculate a contrast evaluation value of an image, a third calculating unit configured to calculate a function indicating a relationship between the defocus amount and the contrast evaluation value calculated at each of a plurality of lens positions, and a fourth calculating unit configured to calculate an adjusting value of the defocus amount based on an extreme value of a function.