This is funny. Normally, people get annoyed if you bump an old thread, but that has not happened yet.
If your 30mm photo tube is like the one I have, you can stick a standard eyepiece in the tube and share the view with another observer. Does the photo tube have a part number I might be able to look up?
The eyepiece takes the intermediate image that is perhaps 15mm inside the tube and reprojects it above the eyepiece to your eyeball. You will need a relay lens like that to re-project the image all the way to your DSLR's sensor. You could try a "high eyepoint" eyepiece and do this "afocally". You find a suitable lens for the DSLR, focus it on the image that is above the eyepiece and have the camera take the place of a human eyeball. I write "suitable" because my strong impression is that people who roll their own often discover a good combination through a fair bit of trial and error. Afocal projection is the same that people use when they take pictures by holding a mobile phone over an eye piece. That will give you an idea about the projected image and the lens you will need.
You can get adapters where someone has done all that work for you, but the good ones from, for example, promicron or lmscope, tend to be pricey. That convinced me to first try "direct projection". Instead of changing the microscope's image to match the camera, you choose a camera and a way to mount it to match the image out of the microscope. You can do this pretty quickly and cheaply with a 38mm photo tube, if you do not need live video. I spent a few hours and less than 90 euros for my first set up, including a 12 megapixel, µ4/3rds camera with a one year, camera store guarantee. I was going to try direct projection with a 30mm photo tube, by decapitating the tube, but found a 38mm one before I could do something rash.