Ophthalmic Apparatus Phase Difference Autofocus Region Selection
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Solution Overview
Problem
Ophthalmic apparatuses face challenges in achieving precise focus detection, especially when the contrast of the target, such as blood vessels in the eye, is low, leading to potential false focus and decreased focus detection precision during phase difference autofocus.
Innovation Solution
The apparatus incorporates a detection unit for phase difference focus detection and a determining unit that identifies a search region with higher focus detection precision, allowing it to adjust and focus on a region with improved precision by including a second subject within the search region, even if the initial subject's precision is below a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase difference AF is performed on the first subject with low contrast, then focus detection is attempted on the intended subject, but focus detection precision becomes lower than the threshold due to low contrast
Solution Approach 1:
The patent applies local quality by selecting a different region (second subject) within the same angle of view that has higher contrast and better focus detection precision. Instead of forcing focus detection on the low-contrast first subject, the system identifies and uses a local area with superior detection characteristics, thereby resolving the contradiction between maintaining focus on the intended subject and achieving sufficient detection precision.
Solution Approach 2:
The patent introduces an intermediary approach by using the second subject as a mediator for focus detection. When the first subject proves unsuitable for reliable detection, the system temporarily uses the second subject with higher precision to establish focus, which then benefits the overall focusing accuracy for the examination.
2Measurement precision
If focus detection is performed on the first subject with low contrast, then the intended subject is examined, but false focus may occur due to insufficient precision
Solution Approach 1:
The patent applies preliminary anti-action by proactively detecting the low contrast condition of the first subject before performing focus detection. The system预先 identifies that focus detection on the first subject would be unreliable and takes preventive action by selecting the second subject instead, thereby avoiding the harmful effect of false focus before it can occur.
Solution Approach 2:
The patent uses feedback by evaluating the contrast and focus detection precision of the first subject, then using this information to determine whether to switch to the second subject. The system continuously monitors detection quality and adjusts the subject selection based on this feedback, preventing false focus by relying only on high-precision detection regions.
3Reliability
If the determining unit strictly selects only the first subject for focus detection, then the intended subject is focused, but focus detection precision remains below the threshold
Solution Approach 1:
The patent applies dynamics by making the subject selection flexible rather than fixed. The determining unit dynamically evaluates the contrast and detection precision of subjects and adapts its selection accordingly. When the first subject proves inadequate, the system transitions to selecting the second subject, creating a dynamic adaptation mechanism that resolves the contradiction between reliability and precision.
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 precision by shifting focus to a region with higher precision, ensuring accurate autofocus even in cases of low contrast, thereby improving the overall focusing capability of the ophthalmic apparatus.
Implementation Method 1
a detection unit configured to perform focus detection by detecting the phase differences between a plurality of signals that are acquired from the image capturing element
Data Source
AI summary
An ophthalmic apparatus is provided with an image capturing optical system and an image capturing apparatus, and optically examines an eye to be examined by performing focus detection using image capturing surface phase difference AF. A focus detection unit calculates data for a focus detection precision map from a defocus amount based on the phase difference detection. In a case in which the focus detection precision of a first subject is less than an established precision, a region determining unit determines a circle or concentric circle region that passes through the first subject, and determines a region that includes a second subject on the focus detection precision map included on the circle or inside of the concentric circle region, and that also has a focus detection precision that is higher than a predetermined precision. The focus detection unit then performs focus detection on the second subject.