Autofocus Device Flare Light Shielding
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Solution Overview
Problem
Biological microscopes face challenges in detecting the focusing state due to low AF light reflectance and interference from flare light, leading to poor S/N ratios and limited use of objectives that generate flare light.
Innovation Solution
An autofocus device with a photodetector, autofocus optical system, and a light shielding member with a diaphragm that satisfies specific aperture and light flux diameter ratios to effectively shield flare light while maintaining a long acquisition range and sufficient S/N ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If AR coating is applied to suppress flare light reflection, then flare light is reduced, but the reflectance of AF light is also reduced, leading to lower S/N ratio
Solution Approach 1:
The pupil plane of the objective is divided into two regions, with AF light directed through one region and reflected light through the other. This spatial segmentation allows separate optical paths for illumination and detection, enabling flare light suppression without compromising AF light detection quality.
Solution Approach 2:
A light shielding member with a specific aperture is introduced as an intermediary component between the tube lens and photodetector. This aperture acts as a spatial filter that blocks flare light paths while preserving the detection of focused AF light, resolving the contradiction between flare suppression and signal quality.
2Object-affected harmful factors
If a light shielding member with aperture is introduced to block flare light, then flare light is suppressed, but the acquisition range may be reduced
Solution Approach 1:
The aperture diameter of the light shielding member is optimized to satisfy a specific mathematical relationship with the light flux diameter. By carefully controlling this parameter, the system achieves flare light suppression while maintaining an adequate acquisition range for practical microscopy applications.
Solution Approach 2:
The aperture is designed to block only the excessive flare light paths while allowing the necessary AF light to pass through. This partial blocking approach selectively removes harmful light without overly restricting the useful light cone, preserving sufficient acquisition range.
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 stable detection of the focusing state even with objectives that generate flare light, ensuring a long acquisition range and maintaining focus during continuous AF, particularly beneficial for biological microscopes.
Implementation Method 1
a photodetector that detects light... light that has passed through the other of the two regions after being reflected by a sample
Implementation Method 2
a light shielding member which is arranged between the tube lens and a light receiving plane of the photodetector and on which an aperture has been formed
Data Source
AI summary
The autofocus device for a sample observation device provided with an objective is provided with a photodetector, an autofocus optical system that includes a tube lens, that guides light to one of two regions of a pupil plane of the objective that has been divided into two, and that guides light that has passed through the other region after being reflected by a sample to the photodetector, and a light shielding member which is arranged between the tube lens and a light receiving plane of the photodetector and on which an aperture has been formed. The autofocus device satisfies 2.1<ΦAP/(2·ΦLD), where ΦAP represents a diameter of the aperture and ΦLD represents a light flux diameter, on the light shielding member, of light reflected by the sample in a state in which the light is condensed on the light receiving plane.