Microscope Autofocus Using Dual Slit Width Variation
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Solution Overview
Problem
Conventional autofocus methods for microscopes have limited depth range, leading to insufficient grating contrast in certain areas, making it difficult to determine the necessary relative shift between the sample and object plane to achieve sufficient contrast for focus adjustment.
Innovation Solution
The method involves projecting a longitudinally extended grating slit and a comparison slit onto the sample, imaging them at an angle to the object plane, and evaluating the width variation of the comparison slit image to determine the direction and amount of relative adjustment needed to restore sufficient grating contrast, using either an unstructured or structured comparison slit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional autofocus methods are used with grating slits, then focus adjustment can be achieved, but the depth range (capture range) is limited and grating contrast becomes insufficient in certain areas
Solution Approach 1:
The patent divides the autofocus function into two complementary components: a grating slit for high-precision focus adjustment within a limited depth range, and a comparison slit for extending the capture range by providing contrast information in areas where the grating slit contrast is insufficient. This segmentation allows each component to operate optimally in its designated depth zone.
Solution Approach 2:
The comparison slit acts as an intermediary element that provides alternative contrast information when the grating slit contrast becomes insufficient. By projecting both slits and combining their images, the system can maintain autofocus functionality across extended depth ranges where either slit alone would fail to provide adequate contrast.
2Adaptability or versatility
If the grating slit plane or camera image plane is inclined to extend capture range, then depth range increases, but grating contrast becomes insufficient in certain areas
Solution Approach 1:
The patent applies local quality by having different regions of the optical system serve different functions: the grating slit provides high contrast for focus adjustment in the focal plane, while the comparison slit provides contrast information in out-of-focus regions. The inclined plane geometry is applied selectively to extend capture range in specific depth zones while maintaining grating contrast where needed.
3Measurement precision
If only grating slit imaging is used, then focus adjustment is precise, but the system cannot determine relative shift direction in areas with insufficient contrast
Solution Approach 1:
The system uses the comparison slit image as feedback information to determine the direction of relative shift between sample and object plane. By evaluating the width variation of the comparison slit image and comparing it with the grating slit image, the control device can identify the direction of defocus and guide the adjustment accordingly, providing feedback for accurate focus restoration.
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 extends the capture range of the autofocus system, allowing for rapid adjustment of the sample and object plane positions to maintain contrast-based autofocus functionality, even in areas with insufficient initial contrast, thereby improving focus accuracy and range.
Implementation Method 1
an autofocus illumination optical unit which projects the grating slit and the comparison slit into the sample
Implementation Method 2
an autofocus imaging optical unit which images the projection of the grating slit onto the autofocus camera to form an grating slit image on the camera, and which further images the projection of the comparison slit onto the autofocus camera to form a comparison slit image on the camera
Data Source
AI summary
An autofocus method for a microscope with an objective which images a sample lying in an object plane, including the steps: projecting a longitudinally extended grating slit which lies in a grating slit plane onto the sample, and imaging the projection of the grating slit onto an autofocus camera; determining an intensity distribution of the grating slit image and from this, deducing a preset for a relative adjustment of sample and object plane; projecting a likewise longitudinally extended comparison slit onto the sample, and imaging the projection of the comparison slit onto the autofocus camera; evaluating the width of the comparison slit image at right angles to the longitudinal extension at at least two sites which are spaced apart along the longitudinal extension, and determining a width variation of the comparison slit image, a gradient of the width variation and a direction of the relative adjustment.