> What my question really is: will my F3.3 mirror have the same coma as > an F6.6 newt if I use a x2 Barlow? This isn't as easy to answer as one might think since the definition of 'same coma' is fuzzy. But strictly speaking, no, a Barlow will not decrease or increase coma. Mel Bartels _______________________________________________ ATM mailing list http://www.atmlist.net/