Tony - it's a Newtonian telescope, not a Dobsonian
The "dob" bit is in reference to the mount, not the optics.
"Pretty long" doesn't really describe too well what you have - is it 6" (150mm) or an 8" (200mm) mirror? There might be a sticker on the OTA near the focuser that describes this - along with the focal ration (f/5 or f/6 probably).
I've had success with my old 200mm newtonian reaching focus with DSLR's (where they wouldn't before hand) by swapping the typical rack and pinion focuser that comes standard with Chinese scopes for a low-profile crayford model from Bintel. Most times this achieves the same result as moving your mirror up the tube - without the hassle. With the shorter focuser body you'll have enough in-travel to reach focus with your camera. The base shoe of the focuser can be changed for one that matches your tube diameter so that it sits nice and flush on the tube.
When you want to use the scope for visual, you'll need to also buy a 35mm (or so) extension tube to bring the eyepiece back out to where the focal point is.