I have always felt 10 power per inch is ideal magnification for most deepsky objects. --- robtaylor3661@comcast.net wrote: From: "Robert Taylor" <robtaylor3661@comcast.net> To: <utah-astronomy@mailman.xmission.com> Subject: Re: [Utah-astronomy] Utah-Astronomy Digest, Vol 71, Issue 17 Date: Wed, 7 Jan 2009 13:22:24 -0700 Nice to hear from you again Jim. I built my 16" as a f/4.45, I was shooting for F/5 but the grind went a little deep and we ended up at 4.45 or 71" (1800 mm). This allows me to stand on my feet nearly all the time and I need about a 6" lift when the scope is straight up, no ladders - ever. This makes the scope a lot easier and faster to use as I never have move a ladder. I understand the benefits of longer focal lengths but in practice the fast f/4.45 works very well and I would not discourage anyone from going that route. Yes you need to use good eyepieces, Naglers work very well. Yes you have to carefully collimate, I sometimes do this twice a night, you get good and fast at it. The grind has to be good but can be done. The 1800m focal length means you have a reasonably wide filed when you need it and it powers up very nicely, remember this is a Dob, how high are you going to go with magnification? As always the best telescope is the one you'll use. Build one that will meet your needs and personal preferences. Bob ************ Message: 1 Date: Wed, 7 Jan 2009 10:04:09 -0800 (PST) From: Jim Gibson <jimgibson00@yahoo.com> Subject: Re: [Utah-astronomy] 13.1 inch Coulter Carcass, free To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Message-ID: <791947.73037.qm@web30701.mail.mud.yahoo.com> Content-Type: text/plain; charset=windows-1252 When I took the class from Brent Watson he wanted all of us (about 5 or 6 in the class) to make f8 or better scopes.? Brent loved long bugger scopes and rightfully so I would say.? Someone more qualified than I can tell you all the benefits of a long scope beside increased contras and increased power, but I recall there a lot of benefits?oh yeah collimation is easier too.? Most everyone in our class wanted to make short (fast) scopes mainly because nobody wanted to use a ladders. ? I went with an f7 (the longest focal length in class) so with a 12.5? mirror which would be 87.5? focal length plus some extra I? believe my sono tube was about 96? long. How do you get?96" in the car you ask?? Can you get 48? in your car?? I could deal with 48? so I cut the sono tube down so I had 2 48? sections. I still had sono tube left over because if I remember right it was about 12? long when I bought it. From the extra piece I cut a 1 foot section then slit it down length wise, took some extra material out till I could get it to fit inside one of the 48? sections forming a sleeve. ? ? I went to the hardware store and got some of those clampy thingys like on a metal tool box and put 3 of them on to fasten the 2 scope ?pieces together.? It worked great! ? I have a ladder and a step stool with long hold onto bars, but a lot of the time I use nothing or the step stool.? Yeah, right now I would need the ladder to see M31. ? I love the way my scope performs. I have never been sorry about going f7, but sometimes I do think I should have listened to Brent and gone f8. ? Chuck Hards or someone can tell you stories about Brent fastening his like f10 to the top of his car and having it come off the tope while heading down the freeway?hehe.? The mirror was just fine. ? Brent had a couple of 12.5? f12 or something scopes ?in his hanger where we took the class. ? The good old days. ? jg _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com