10" F/4.7 Modified Skywatcher Reflector, 38mm Orion Q70, 17mm Modified Ultima LX, 10mm TeleVue Delos, 7mm Pentax XL.
Quote:Thanks for the really interesting replies. I should have spotted the other thread! Oops.I hadn't come across the idea of field curvature before, but your explanations make sense to me. In fact my impression was that stars just wouldn't come to focus at all around the edge of the field, but I'll go back and have another look as soon as I get some clear sky...To complicate the issue further, I do have some built-in astigmatism of my own, but I don't think this is a big part of the problem as it's only just noticeable in a TV 25mm Plossl.I'll let you know!
Quote:Are not at least some eyepieces made to accommodate the field curvature typical of most telescopes? To be sure, not all eyepieces are made for a flat image surface only. It would be most handy if all eyepieces were provided with the designed field curvature and recommended minimum f/ratio.
Quote:Don,The *vast* majority of telescopes used by visual observers inherently have field curvature of the same sign, it being concave toward the sky. There can be a not inconsiderable range, but it should be 'safe' to make an eyepiece so that its own field of best focus is curved to fit a typical or mean radius.I'm surprised at the reversal (and degree) of curvature for the shorter f.l. eyepieces in the list you just posted.