David, why are you using a camera lens?
I have two "microscope adapters" for 35 mm cameras. One is a generic T-mount type with no internal optics, the other is a Nikon Microscope Adapter Model 2 that contains a field lens. The fronts of both attach to the microscope drawtube, hold the microscope eyepiece. The rears attach directly to a Nikon body.
Its been a while since I've used either, but IIRC I got images that filled the frame. You may need a wide field ocular.
Take a look at http://www.microscopy-uk.org.uk/mag/indexmag.html, there may be an article there that will tell you what to do.