I use a Canon 1000d and if yours has live view or even USB connection you can use a natty software programme called 'Astrophotography Tool (APT)- it's really easy to use the live down load and programme features to programme a run of say, 5 sec exps for deep sky, then use them to focus on. Course it means lugging a laptop outside! Of r the moon you could use much shorter exps and twiddle with the focus then.
It works on all EOS cameras.
www.ideiki.com/astro/
Graham