An open-source alignment method for multichannel infinite-conjugate microscopes using a ray transfer matrix analysis model

TL;DR

This paper introduces an open-source, image-based alignment method for multichannel infinite-conjugate microscopes that uses ray transfer matrix analysis and magnification measurements, eliminating the need for additional hardware.

Contribution

It presents a novel alignment algorithm leveraging ray transfer matrix analysis and image magnification measurements for open-source microscopes, improving simplicity and accessibility.

Findings

Alignment accuracy is comparable to the microscope's axial resolution.

The method effectively detects and corrects lens misalignments.

Open-source implementation validated with 3D-printed and commercial microscopes.

Abstract

Multichannel, infinite-conjugate optical systems easily allow implementation of multiple image paths and imaging modes into a single microscope. Traditional optical alignment methods which rely on additional hardware are not always simple to implement, particularly in compact open-source microscope designs. We present here an alignment algorithm and process to position the lenses and cameras in a microscope using only image magnification measurements. We show that the resulting positioning accuracy is comparable to the axial resolution of the microscope. Ray transfer matrix analysis is used to model the imaging paths when the optics are both correctly and incorrectly aligned. This is used to derive the corresponding image magnifications. We can then extract information about the lens positions using simple image-based measurements to determine whether there is misalignment of the objective lens to sample distance (working distance) and with what magnitude and direction the objective lens needs to be adjusted. Using the M4All open-source 3D printable microscope system in combination with the OpenFlexure microscope, we validate the alignment method and highlight its usability. We provide the model and an example implementation of the algorithm as an open-source Jupyter Notebook.