Why not go for a 16" f/16.5? See the mirror being offered at: http://cgi.ebay.com/ws/ eBayISAPI.dll?ViewItem&category=31745&item=5917131317&rd=1 Brent Watson can attest to the benefits of observing from 20 feet off of the ground. The seeing is always steadier from such heights. Those with vertigo will stay away so lines for your scope will be shorter. You can get away with a very small secondary obstruction too and collimation is a cinch. No need for the correction of Naglers or a Paracorr either. Of course you need a flatbed to transport both the tube, counterweight, and extension ladder. Remember, look with both eyes for best effect when viewing a first quarter moon from a dozen steps up the ladder. Those purple crescents make for a great trip! dlb