On a related note, if one's willing to forego proper mechanics and lighting, for imaging small stuff you only need a digital video camera and a microscope objective lens (or just a photographic lens with some macro rings). I got good results [1] with a machine vision camera from PGR (comparable to RPi camera module) on a tripod pointed at a slide held in a "third hand", with desk lamp shining from behind ("oblique illumination"). Yes, one can easily move it sideways and focus by hand.

[1] https://vimeo.com/user12237688 (technical details in the description)