Focus Detection Pixels Correcting Two-Image Interval for Asymmetrical Pupils
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Solution Overview
Problem
Focus detection devices using the pupil-division phase difference method face errors in calculating defocus amounts due to asymmetrical images formed by asymmetrical pupils, leading to inaccuracies in correlation calculations, especially with significant defocus amounts.
Innovation Solution
A focus detection apparatus and method that includes focus detection pixels receiving light fluxes from a photographing optical system, a memory for storing correction values based on light flux width, and a controller to calculate the width of the light flux and correct the two-image interval value to accurately determine the defocus amount, reducing errors by using correction coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If correlation calculation is carried out using asymmetrical images formed by pupil-division, then focus detection can be performed, but error in obtaining two-image interval becomes large
Solution Approach 1:
The patent applies parameter changes by switching between a first AF sensitivity (with conversion coefficient) for in-focus positions and a second AF sensitivity for significant defocus states. This dynamic parameter adjustment compensates for the asymmetry-induced errors in two-image interval measurement, thereby maintaining defocus amount calculation reliability across different focus states while preserving measurement precision.
Solution Approach 2:
The patent implements dynamics by dynamically selecting different AF sensitivity parameters based on the detected focus state. The system transitions from using a first AF sensitivity near the in-focus position to a second AF sensitivity in significant defocus states, enabling adaptive compensation for asymmetrical image effects and ensuring reliable defocus amount calculation throughout the focusing range.
2Measurement precision
If switching between first and second AF sensitivity is implemented, then error is reduced, but device complexity increases
Solution Approach 1:
The patent manages algorithm complexity through parameter changes by switching between two pre-defined AF sensitivity sets (first and second AF sensitivities) rather than implementing complex real-time calculations. This approach reduces measurement precision errors while keeping the algorithm relatively simple, as the switching logic is based on predetermined thresholds and lookup tables.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing multiple AF sensitivity parameters (first and second AF sensitivities) for different focus states. This preparation work is done in advance, allowing the system to simply switch between pre-computed values during operation rather than performing complex real-time calculations, thereby reducing both measurement errors and runtime computational complexity.
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
The solution effectively reduces calculation errors in defocus amounts by correcting the two-image interval value, ensuring high precision in focus adjustment even with asymmetrical pupil shapes, and maintaining continuity in defocus amount calculations across different threshold values.
Implementation Method 1
a focus detection section that detects a two-image interval value in a pupil-division direction, based on output of the focus detection pixels
Implementation Method 2
focus adjustment for the photographing optical system using a pupil-division phase difference method
Data Source
AI summary
A focus detection apparatus, comprising, focus detection pixels that receive a pair of light fluxes resulting from pupil division of light flux, a memory that stores correction values in accordance with width of the imaging light flux in the pupil-division direction relating to a two-image interval value, and a controller having a focus detection section, a light flux width calculation section, and a defocus amount calculation section, wherein the light flux width calculation section calculates the width of the imaging light flux in the pupil-division direction, and the defocus amount calculation section calculates defocus amount of the photographing optical system based on the two-image interval value, wherein the focus detection section detects a first two-image interval value and corrects the first two-image interval value based on the correction values and the width of the imaging light flux in the pupil-division direction to obtain a second two-image interval value.