The two collimators are in stainless steel from Thorlabs. Our new design is agronomies. We also improved the light collimation for more efficiency. To pass from one setting to the other, just screw the stainless-steel collimator in the correct position.
This is a companion discussion topic for the original entry at https://www.ebay.com/itm/Cuvette-Holder-Transmission-Absorption-Fluorescence-Spectroscopy-ThunderOptics-/283583313747