When you set up PHD guiding pick a fairly bright star to guide on.
I set up an imaging session last night with the idea of taking 20 x 3 minute subs with my 120 f/5 achromat.
Spent the first 5-10 minutes after setting everything up (no permanent site) getting the focus as near as perfect with DSLR Focus actually I was happy with this works a treat.
Set up PHD on a smallish dull star at 3.5s exposures PHD calibrated and said guiding OK.
1st image taken came out fine, so I went inside for an hour, then when I came out again I found that PHD had lost the target star sometime during the second expsoure and all I had for the nights effort apart from the 1 good sub was a series of star trails.
I can only assume that the guding failure may have been caused through some low cloud coming out of nowhere blocking the light from the dim guide star I had picked.
So I suggest if you do set up like I did
a) pick a bright as possible guide star
b) wait until at least a quarter of the subs have been taken before leaving the mount too go it alone.
