Focus Detection Apparatus Shading Correction via Pre-calculated Coefficients
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Solution Overview
Problem
Existing focus detection systems face challenges in achieving accurate shading correction and efficient calculation of conversion coefficients, leading to degraded focus detection performance due to vignetting and varying aperture values across different lenses.
Innovation Solution
A control method for focus detection that acquires light quantity information and converts the first aperture value into a second aperture value based on the focus detection position, setting a conversion coefficient according to the second aperture value and exit pupil distance to improve focus detection accuracy and reduce calculation processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If highly accurate shading correction is performed, then focus detection accuracy is improved, but calculation processing time increases
Solution Approach 1:
The patent pre-calculates and stores conversion coefficients in a table structure before actual focus detection operations. The coefficient calculation unit computes conversion coefficients for various aperture values and image heights in advance, storing them in a coefficient storage unit. During focus detection, the system simply retrieves the appropriate pre-calculated coefficient based on current aperture and image height parameters, avoiding time-consuming real-time calculations while maintaining high accuracy
Solution Approach 2:
The patent divides the conversion coefficient calculation into separate independent components: aperture value-based coefficients and image height-based coefficients. These are stored as separate tables and combined through multiplication during runtime. This segmentation allows the system to handle complex shading correction through simple table lookups and basic arithmetic operations rather than complex real-time calculations
2Measurement precision
If conversion coefficients are calculated for each lens model, then focus detection performance is improved, but device complexity increases
Solution Approach 1:
The patent uses light quantity information (vignetting characteristics) as a key parameter to adapt conversion coefficients to different lens models. Instead of creating separate coefficient sets for each lens, the system calculates conversion coefficients based on the actual light quantity distribution measured for each lens-aperture combination. This parameter-based approach allows flexible adaptation to any lens model without increasing structural complexity
Solution Approach 2:
The patent creates a universal coefficient calculation and storage system that can handle multiple lens models, aperture values, and image heights through a single unified table structure. The conversion coefficient table is designed to accommodate various lens types by using generic parameters (aperture value, image height, light quantity information) rather than lens-specific identifiers, making the system universally applicable across different lens models
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 approach enhances focus detection performance by accurately calculating conversion coefficients and performing shading correction, thereby improving the precision and speed of focus detection across various lenses and imaging conditions.
Implementation Method 1
an imaging device, which has a great number of pixels two-dimensionally arrayed such that a relative positions of photoelectric conversions unit are deviated from microlenses and the optical axis thereof
Data Source
AI summary
Light quantity information of an imaging optical system is acquired according to a focus detection position in an imaging screen. Conversion is performed from the light quantity information and a first aperture value of the imaging optical system, so that the first aperture value is converted into a second aperture value according to the focus detection position. A conversion coefficient is set according to the second aperture value and an exit pupil distance. A correction value to correct output signals from an imaging unit is obtained according to the second aperture value and an exit pupil distance.