Fundus Camera Phase Difference Autofocus Mechanism
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Solution Overview
Problem
Conventional fundus cameras face focusing errors due to individual variations in eye aberrations, such as spherical aberration and astigmatism, when attempting to align focus split target images, leading to out-of-focus fundus images.
Innovation Solution
A fundus camera design incorporating a focus target projection unit with a split optical element, a phase difference detection unit, and a focus link mechanism to interlock the focus target projection and focusing lens, allowing for precise alignment and correction of focus target images based on phase difference detection between signals from image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If focus split target images are aligned in a predetermined positional relationship to achieve focusing, then focusing ease is improved, but focusing accuracy deteriorates due to individual eye aberrations
Solution Approach 1:
The invention divides the focus detection function into two independent parts: (1) focus split target alignment for ease of operation, and (2) wavefront sensor-based phase difference detection for accuracy. The wavefront sensor separately measures optical path differences caused by eye aberrations, allowing the system to compensate for individual variations without affecting the alignment procedure.
Solution Approach 2:
The invention introduces a wavefront sensor as an intermediary measurement device between the eye and the focus detection system. This intermediary independently characterizes the eye's optical aberrations, enabling the system to adjust for individual differences and achieve accurate focusing despite variations in eye optics.
2Object-affected harmful factors
If fundus illumination light flux and observing/photographing light flux are incident upon different areas to eliminate corneal reflection, then reflection elimination is improved, but focusing accuracy deteriorates due to aberration variations
Solution Approach 1:
The wavefront sensor acts as an intermediary that independently measures optical path differences caused by corneal and internal eye aberrations. This separate measurement allows the system to compensate for the effects of dividing the light flux into different incident areas, maintaining focusing accuracy despite the spatial separation of illumination and observation paths.
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
Enables accurate focusing and correction for individual eye aberrations, ensuring high-precision autofocus even in cases of significant optical distortions, preventing focusing errors and improving image clarity.
Implementation Method 1
a split optical element configured to split a light flux passing through the focus target
Implementation Method 2
a phase difference detection unit configured to detect a phase difference between the focus target images based on a difference between signals output from the image sensors
Data Source
AI summary
A fundus camera includes a focus target projection unit including a focus target located at a position conjugate with a fundus of a subject's eye, a split optical element configured to split a light flux passing through the focus target, and a focus target illumination light source configured to illuminate the focus target, a fundus photographing optical system including a focusing lens, a focus link mechanism configured to interlockingly move the focus target projection unit and the focusing lens in a direction of an optical axis, at least two lenses located behind a plane optically conjugate with the imaging plane of the fundus photographing optical system and outside an optical axis of the fundus photographing optical system, image sensors respectively located behind the two lenses, and a phase difference detection unit configured to detect a phase difference between the focus target images based on signals output from the image sensors.