centre white spot

[Joss]

Hello everyone,
complete beginner to microscope photography. An Olympus BH has come my way, and I've attached a Canon EOS 1100D to it via a phototube, with a 3.3x photo eyepiece. My first attempts show this bright centre spot that you can see on the attached image (the image is a screen shot of what I can see using Live View - the image through the microscope eyepiece is fine). I expect this is a very basic thing, but I'd be grateful for any pointers on how to sort it out.
thanks, Joss

[75RR]

... the image through the microscope eyepiece is fine).

Does that include the image through the trinocular eyepiece?

See links:
viewtopic.php?f=15&t=882

[Joss]

Yes, if I replace the phototube with an eyepiece lens, the image is normal through the trinocular tube. Thanks for the links.
Joss

[Oliver]

The bright spot could be due to the reflection of light inside the phototube. once had a similar issue. Closing the koehler diaphragm resolved this (should you microscope have this), alternatively you might want to check if the inside of the tubes are sufficiently dark, to reduce reflection.
Oliver.