The image to the right shows how to connect a Celestron t-adapter/2x barlow to a Canon EOS DSLR body. A t-ring is needed to connect the adapter and camera body together.
Once fitted together, the adapter allows for prime focus (no eyepiece used) photography on an astronomical telescope. This adapter has a couple of advantages that overcome focusing issues with two types of telescope. With having an in built barlow, you will find infinity focus possible with Newtonian telescopes that do not have enough inward travel.
By unscrewing the barlow lens, the adapter also becomes a useful extension tube for refractors. Also by unscrewing the lens from the adapter you will find a thread to accept 1.25″ filters
To use. Simply insert the adapter into the eyepiece holder and focus manually.