[raymo]

I'm sorry, but Danh is incorrect in saying that you have to do all the mods
he lists in order to get your 10" SW Dob to come to focus. All SW Dobs, collapsible or otherwise, can be used for astrophotography out of the box.
You simply unscrew the eyepiece holder and replace it with the T ring. Canon,
and as far as I know, most Nikon, DSLRs come to focus with the focuser
racked out about 10-12mm from the fully in position.
Danh was correct in many cases, but not for SWs.
As previously mentioned, you will suffer with field rotation, which for your scope will limit you to exposures of 15-20 secs. For your camera
ISO 800 and exposures[subs] of 15 -20 secs is a good starting point.
raymo