Spectral DJ - Modular Filter Rotator System for Microscopy

Background: One of the most economical ways to paint microscopic subjects with extraordinary color is by utilizing polarized light. Highly birefringent subjects such as crystals and minerals and certain critters can become vibrantly colored when placed between two crossed polarizers. When additional polarization altering optics are added to the light path over the initial polarizer, these colors can become drastically altered, leading to unpredictable and often beautiful effects. The colors can be intense and punchy, dark and moody, or take on the delicate character of pastels or watercolor. To discover these color spaces, it's necessary to rotate the optics in different ways, and that's difficult if you've just got them stacked on top of each other.

These parts: Introducing the Spectral DJ system! This is a modular system of snap-together filter rotators, each designed to hold a single 45mm optic and fit over the field lens of your microscope. Each optic can then be rotated independently by a knob that turns the optic in a 2:1 gear ratio (one full turn of the knob = half turn of the main optic). Start the stack with a linear polarizer, then add waveplates or other birefringent materials on top and just start exploring! I recommend picking up a full wave and a quarter wave plate (there's a guy who sells these cheap on eBay) but you can also experiment with cellophane, plexiglass, and really anything else that does something funky between crossed polarizers. Don't forget to try rotating the initial polarizer too - it doesn't need to be crossed with the analyzer for highly birefringent subjects.

Compatibility: At the time of writing, this system comes with a mounting system designed to press-fit into scopes with a 45mm filter receptacle at the field lens. That includes the Olympus BH2 and the Nikon Labophot 2, but also the various BH/CH2 clones on the market such as the Amscope B490/B390. However, the mounting base is designed in two pieces such that a different field lens mount could be easily designed and attached to the same base component.

Printing specifics: These parts should be printed with a low friction material - regular PETG works great. I've also printed some in PETG with teflon additives. I would not use PLA as it's not as slick. This part includes some fine geometry in the gears and outer race housings, so print with a .4mm nozzle and use fine layers - I did most of mine at .16mm. Use random seams and arachne, 3 wall loops, and concentric top and bottom layers. You might want to tune the outer wall speed down a little to ensure the gear geometry comes out very clean.

The rotator comes as an assembly - it technically can be printed in place, but I strongly recommend splitting it to objects and printing them spaced out on the build plate.

Assembly: The outer housing is flexible enough to insert and remove both gear components with light force. Install the knob first, then angle in the filter gear such that it meshes with the knob teeth first and just work around the perimeter until it pops in. If you have a little bit of light teflon grease around, you can shoot some in around the perimeters of the gears to make them turn more smoothly. The 2 components of the base fit together with a snug press-fit. Install the first rotator on the base clips with the knob protrusion over the indicator arrow on the base. This one should snap pretty securely and is designed to be removed together with the base assembly. Subsequent filter rotators can be installed in one of 5 different positions on the previous rotator - you can arrange them however seems best to you! They should snap on and off each other easily. If you encounter resistance, try prying from a different angle.

If you use these to create cool stuff that you share publicly, please consider letting people know what you're using and where you got them from! Microscopists are a pretty widely dispersed group of hobbyists, so word of mouth is important for spreading new techniques and ideas.