Lost 3 hours of M31 shots because my focus slipped and I kept shooting
Learned the hard way last Tuesday that you have to check focus every 20 minutes or so when the temp drops, my stars went from pins to soft blobs and I did not notice till I stacked them. 3 hours of data in the trash, now I set a timer on my phone. Anybody got a cheap way to autofocus a DSLR rig without dropping $300 on a controller?
Read on Cloudy Nights that a cheap intervalometer plus a Bahtinov mask can sort of fake it, you just refocus by hand every time the timer fires. The mask makes it easy since you get that spike pattern instead of guessing off star size. Runs maybe $40 total and beats babysitting the screen all night.