Lens Apparatus Autofocus Correction with Extender Pupil Diameters
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Solution Overview
Problem
The existing methods for improving autofocus accuracy when an extender is attached suffer from defocus issues due to spherical aberration fluctuations, leading to incorrect focus correction values and increased costs for measuring manufacturing errors.
Innovation Solution
A lens apparatus with a focus detection unit and controller that determines a correction value based on the diameters of the pupils of the focus detection and image capturing optical systems, including the extender optical system, to correct focus detection results and reduce defocus when an extender is attached.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the focus correction value is calculated based on the focus correction value when the extender is not attached (as in JP 2016-90815), then the autofocus accuracy is improved when the extender is not attached, but the focus correction becomes incorrect when the extender is attached due to spherical aberration fluctuations
Solution Approach 1:
The invention changes the parameter used for focus correction from a fixed value (calculated without extender) to a dynamic value that adapts to the extender magnification. The focus correction value is now calculated by multiplying the extender magnification by the focus correction value of the single lens, allowing the system to adapt to different optical configurations and eliminate defocus errors when extenders are attached.
2Measurement precision
If the lens apparatus stores the focus correction value when the extender is attached, then the focus correction accuracy is improved, but the device complexity and cost increase due to requiring measuring equipment for each apparatus
Solution Approach 1:
Instead of requiring physical measurement equipment for each apparatus, the invention creates a computational model (copy) of the focus correction behavior. The system calculates the focus correction value using the extender magnification and the single lens focus correction value, replicating the effect of measured values without the need for expensive measurement equipment for each device.
Data Source
AI summary
A lens apparatus detachably attachable to an image capturing apparatus including a focus detection unit having a focus detection optical system and performing focus detection process, and a controller controlling driving of a focusing lens unit based on a result of the focus detection process, via an extender including an extender optical system, includes an image capturing optical system including the focusing lens unit, and a determination unit determining a first correction value used for correcting the result of the focus detection process. When the lens apparatus is attached to the image capturing apparatus via the extender, the determination unit determines the first correction value using first information regarding a diameter of a pupil of the focus detection optical system and second information regarding a diameter of a pupil of an optical system including the image capturing optical system and the extender optical system.