Autofocus Correction for Converter Lens Aberrations
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Solution Overview
Problem
Existing autofocus methods, such as contrast AF and phase-difference AF, face challenges in accurately correcting focus detection errors caused by aberrations in optical systems, particularly when a converter lens is attached, as they fail to adequately account for changes in magnification and aberration effects across different directions and frequencies.
Innovation Solution
The proposed image capturing apparatus and method implement a precise correction mechanism by calculating and applying vertical/horizontal, color, and spatial frequency BP correction values to the focus detection results, using a combination of phase-difference and contrast detection methods to account for aberrations and magnification effects, ensuring accurate focus detection across various imaging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the focus detection error is corrected by magnifying the error amount by the square of the magnifying power of the converter lens, then the focus detection error in the vertical direction is corrected, but the focus detection error cannot be sufficiently corrected due to changes in horizontal direction characteristics and frequency characteristics
Solution Approach 1:
The patent segments the focus detection error correction into three distinct components: vertical/horizontal BP correction values (separating directional corrections), color BP correction values (separating wavelength-based corrections), and spatial frequency BP correction values (separating frequency-based corrections). This segmentation allows each component to address specific aspects of the error independently, resolving the contradiction by making the correction system adaptable to different directions and frequencies while maintaining high measurement precision.
Solution Approach 2:
The patent applies local quality by providing different correction values for different regions of the optical system. Specifically, it calculates separate correction values for vertical and horizontal directions, for different color channels (R, G, B), and for different spatial frequencies. This localized correction approach ensures that each specific error characteristic is addressed with a tailored correction, thereby achieving both high precision and broad adaptability.
2Productivity
If a converter lens is attached to the image capturing apparatus, then the magnifying power increases, but the aberration of the optical system is magnified, causing larger focus detection errors
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for vertical/horizontal BP, color BP, and spatial frequency BP based on the known aberration characteristics of the optical system. These correction values are computed in advance for various shooting conditions and stored in a correction value storage unit. During actual focus detection, the appropriate pre-computed correction values are retrieved and applied, eliminating the need for real-time complex calculations and enabling efficient compensation for the magnified aberrations caused by the converter lens.
Solution Approach 2:
The patent implements feedback by using the detected focus detection error to select and apply appropriate correction values from the stored correction data. The system continuously monitors the focus detection results and applies the corresponding correction values based on the shooting conditions (such as focus detection area, wavelength, and spatial frequency), creating a closed-loop system that compensates for the magnified aberrations and maintains measurement precision despite the high magnifying power.
3Measurement precision
If multiple correction values (vertical/horizontal, color, spatial frequency) are calculated and applied, then the focus detection accuracy is significantly improved, but the device complexity increases
Solution Approach 1:
The patent reduces device complexity by performing the complex calculations of multiple correction values in advance and storing them in a correction value storage unit. During actual operation, the system only needs to retrieve and apply the pre-computed correction values based on the current shooting conditions, which significantly simplifies the real-time processing requirements and hardware complexity while maintaining high measurement precision.
Solution Approach 2:
The patent uses copying by storing correction values for different conditions (vertical/horizontal directions, color channels, spatial frequencies) in a correction value storage unit. Instead of recalculating complex correction algorithms in real-time, the system copies and applies the appropriate pre-computed correction values from storage, which reduces the computational burden and device complexity while achieving accurate focus detection correction.
Data Source
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AI summary
An image capturing apparatus capable of executing autofocus by at least one of a phase difference detection method and a contrast detection method using an image signal obtained from a set focus detection region and from which an imaging optical system and a converter lens are detachable. The image capturing apparatus comprises: conversion means for converting aberration information indicating a spherical aberration of the imaging optical system based on a magnification and aberration information of the converter lens in a case where the converter lens is mounted; calculation means for calculating a correction value for correcting a difference between a result of the autofocus and a focus condition of a captured image; and control means for controlling a position of a focus lens based on the result of the autofocus that has been corrected using the correction value.