DoN. Nichols wrote:

snip

Hmm ... at what angle do you get total internal reflection?
IIRC it is a function of the index of refraction. And while binocular
prisms get TIR at 45 degrees, the light enters and exits at close to 90
degrees, thanks to the design of the prism. If you have the light
entering at 45 degrees on one face, it will be bent towards the other
face so the angle will be steeper than 45 degrees.

And -- *if* you got TIR with the glass (say you made a full
45-45-90 prism to get the entrance angles right) you would get nothing
through to your eyepiece.

So I think that the semi-silvered is the better choice.

Hmm ... the light is not focused where it passes through the
mirror, so you might be able to take a first-surface mirror and scribe
through the silvering in a pattern to get something like 30-45%
reflection, and then you might be able to use it. I've seen scribed
patterns in mirrors in SLR cameras, with the CDS cell for metering
behind the scribed section.

A scribed mirror is a fascinating idea! But it seems like it is done by
total internal reflection in this microscope. I've yet to completely
absorb the intricacies of the optical system, but it's interesting to
note that the reflector pivot is not directly above the centre of the
objective lens. It's slightly in front on the lens, i.e., closer to the
light source.

I also need some lens-removing tools. Not sure what they're called. I'll
probably post a message about those at r.c.m in the next few days.

Thanks for the help.

Best wishes,

Chris