It allows us to connect an eyepiece, or a CCD camera to a camera lens.
For the eyepiece end, it features a nice thumb-screw with compression ring.
And for the camera side, it has a standard Canon EF/EF-S mount.
I've tested it straight through with an eyepiece, and it reaches infinity focus without problem. If a star diagonal is used, one must insert an 2x Barlows in front of the diagonal.
When used with my Canon 200mm f2.8L, it works as a rich field scope in the straight through configuration. With a diagonal is inserted together with a 2x Barlows, it works as a nice medium power 70mm refractor.
I can offer these small adapters at $49 USD each airmail shipped.