Focus Detection for Transparent Objects Using Evaluation Value Minimum
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Solution Overview
Problem
Existing observation devices face challenges in accurately and efficiently performing focus adjustment for transparent objects like non-colored cells, as the contrast AF method fails to detect a peak at the in-focus position, leading to erroneous determination of local minimum positions due to environmental and structural variations.
Innovation Solution
An observation device with an image sensor and AF detection circuit that calculates a focus evaluation value, detecting the minimum value between focus positions of multiple peaks and determining the in-focus position based on specified differences between these peaks, ensuring accurate and rapid focus adjustment regardless of the observation environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the contrast AF method is used to detect focus position, then the focus evaluation value can be calculated, but for transparent objects like non-colored cells, the focus evaluation value does not become a peak at the in-focus position, leading to erroneous determination of local minimum position
Solution Approach 1:
The patent changes the detection parameter from relying on contrast peak positions to detecting the local minimum position of the focus evaluation value. By detecting the minimum value between two peaks and using the distances from each peak to this minimum as detection parameters, the system achieves reliable focus detection for transparent objects where traditional peak detection fails.
2Measurement precision
If the focus lens is driven to the close-up end and infinity end to detect local minimum position, then the local minimum can be detected, but a lot of time is required for detection
Solution Approach 1:
The patent performs preliminary detection of peak positions in the focus evaluation value curve. By identifying the two peaks first and then detecting the minimum value between them, the system avoids time-consuming full-range scanning to the close-up and infinity ends, significantly reducing detection time while maintaining accuracy.
3Productivity
If determination is made based on contrast magnitude relationship, then focus position can be detected, but there is the possibility of erroneous determination of local minimum position due to slight change in contrast
Solution Approach 1:
The patent uses feedback by detecting the distances from each peak to the local minimum position and comparing these distances against specified ranges. This feedback mechanism validates the detected local minimum position, ensuring accuracy even when contrast values change slightly, and prevents erroneous determination.
4Device complexity
If detection relies on the assumption that local minimum position is at an intermediate position between two peaks, then detection can be simplified, but depending on observation environment, the local minimum position is not limited to being at an intermediate position
Solution Approach 1:
The patent applies a dynamic detection approach by not fixing the local minimum position assumption to only intermediate positions. Instead, it detects peaks first and then searches for the minimum value between them, allowing the local minimum to be positioned flexibly according to actual observation conditions while maintaining detection accuracy across different environments.
Data Source
AI summary
An observation device, comprising an AF detection circuit that calculates an evaluation value showing a larger value as degree of focus increases, based on an image signal, and a controller that detects focus position where focus is achieved based on the evaluation value, wherein the controller, when peaks of the evaluation value have been detected for different focus positions, detects a minimum of the evaluation value between focus positions of the plurality of peaks, and in the event that a first difference between a first peak, among the plurality of peaks, and a focus position of the minimum, and a second difference between the minimum and a focus position of a second peak, among the plurality of peaks, are within respective specified ranges, detects a focus position where focus is achieved based on the focus position of the minimum.