You could also do the opposite - the lens is fixed to an inner sleeve of Delrin or such which has grooves that coincide with bushings in the body (that the sleeve can slide past the pill.) There are also 2 guide pins on opposite sides of the inner sleeve. The head would “snap” into place with Delrin bushing and o-ring, that it can only rotate. Two helical grooves are cut inside the head and register the pins on the inner sleeve. So a twist of the head would cause the lens to move in and out. Basically an upside-down lipstick tube…

It would be complicated to machine, but the action of watching the lens magically slide in and out would be so freaking cool!