Hi Debbie - I have an 10" F/4.5. For that size scope, there's obviously not much of a length/weight difference, but it would certainly increase with aperture. I don't have any particular trouble collimating mine, using a cheshire eyepiece. Perhaps the biggest issue you'll run into is the limiting FL of your eyepieces. I have a 35mm Ultima that is very hard to use at F/4.5 (works fine in my F/10 SCT). Somewhere around 32mm is probably a practical upper limit. At F/5, you might notice the secondary a bit less with the wide-field eyepieces. Michael I was wondering if people would rather have an f/4.5 or an f/5 dobsonian reflector. I've looked through both and can't see any major difference. The f/5 scope would be easier to collimate but the f/4.5 would be easier on my knees. What do you guys/gals think? Debbie _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com