Anyone does microscope photography here?

[LXH]

I've just gotten a microscope and adapter to a DSLR to play around, but somehow the pictures come out with a bright light in the middle. When I look through the eyepiece without the camera, that doesn't happen. I heard that it might be because the inside of the adapter is too reflective, so I tried putting a black cardboard paper on the sides of the adapter, but it didn't help. Does anyone know why this is and how I can fix it? Thanks!