I made this a few months ago, but hadn't gotten around to posting it. Now that I'm using it, it seemed like a good time.
This is an adapter to mount a Canon EF compatible camera to an old Nikon lab microscope.
It is based on my EF Mount I designed a while back: http://www.thingiverse.com/thing:10829
The adapter itself, the microscope the adapter was made for, a few photos of pigment splotches on a professionally printed post card, and a single bottom-layer trace of black PLA, after it was extruded directly onto a microscope slide..
More information, more photos, and a video can be seen here: http://www.protoparadigm.com/2012/01/what-to-do-with-a-3d-printer-make-a-custom-microscope-adapter/
To make this, print each of the two STL files, then force-fit them together. When I did this, it did not require any glue, heating, or anything. A fair bit of force popped them right together and they're fairly permanently attached it seems.
If you'd like to compile it in Openscad, you'll also need the EFMount.scad file in the same directory. I've attached it to this thing as well for convenience.
With a little bit of support, you MAY be able to print the whole thing as one part. You can compile it as an assembly in Openscad. I have not tried this.
This is a purely mechanical adapter, there are no optics. Because of this, the focal length for the camera is different than for the eye piece and you'll have to do your focusing through the camera. Also, your aperture is determined by the microscope lens, so the camera side of things is wide open, you can only adjust ISO and shutter speed.