Adding an IRIS diaphragm to a microscope objective can give really good DOF control when using it as a more traditional camera lens in reflected light mode.

For use an SK-12 iris -- the iris is captured between the two friction fit rings, turning the objective opens or closes but this version does NOT capture the objective, so be sure not to pull or bump it or it WILL fall off!!

Print threads at 0.1mm

Feel free to scale XY (not Z) for a good fit.