I have uploaded the picture of the microscope to be hacked.

I have found out that there is an image plane inside the eyepiece of the microscope, surrounded by a nice aperture that defines the FOV.  That's a good place to put a sensor, but:

* it will obscure the view through the microscope, so it has to be placed near an edge of the aperture. I'm not sure if it will work too well, I'd prefer placing it in the center.

* it's tight there.

Another option is to put a semitransparent mirror inside the tube the eyepiece is mounted to, drill a big hole in the tube and place the sensor perpendicularly. So, I'll have unlimited space there, but there are drawbacks as well.

* semitransparent mirror will lower the light transmission of the microscope

* two low-R reflections will be added into sensor's optical path, it WILL get problematic.

That's the main thing I'm thinking on now.