Thanks guys for the simple replies, that's exactly what I was after! Steffen, you've got me wondering whether maybe I should go the barlowed collimator, probably doesn't hurt to have the extra peace of mind.
At least none of you have told me I need to get a purpose-made, custom-built apparatus designed by NASA which can only be operated by an astrophysicist... that's the impression a lot of other forums give!
