I bought this no-name DSLR adapter from Aliexpress for about $53. It came with a T2 adapter ring for Canon EOS cameras and also eyepiece adapters for stereo microscopes. The adapter can be inserted into a standard eyepiece port (23mm diameter) or on the phototube of the microscope. The adapter produced good (but not great) results on my compound microscope, but bad results on my stereo microscope. Here the image was somewhat blurry. The overall manufacturing quality is high. The supplied T2 adapter ring (which is the interface to the camera) was for Canon EOS cameras, and can be exchanged for other cameras.
The optics picks up the image from the tube of the microscope and projects it on the sensor. For this reason, the adapter is parfocal. This means that both eyepieces and camera can be brought into focus simultaneously.
Product link: DSLRAdapter