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You have the wrong end of the stick. You cannot use an alt/az mount for
long exposures, due to a phenomenon called field rotation, which is why
mounts that can be used in both EQ and alt/az modes are becoming popular.
You can mount a Dob OTA on an EQ mount, as many have done.
With a manual Dob at high powers a target will stay in view for a few seconds only, and nudging it to keep an object in view becomes easier with practice.
If you are not wanting to do long exposure imaging in the foreseeable future, a motorised [Go To] Dob is a great choice because you get
decent aperture and motorised tracking [no more nudging], and exposures up to around 30 secs are possible. If you want to do ANY
imaging with camera attached to the focuser, you must make sure that
the Dob you choose has enough back focus for prime focus imaging. Many brands don't. Skywatcher ones do.
raymo
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