Patrick wrote,
If anyone is interested, I have S&T going back to the first issue in my library. If y'all can come up
with the issue the article is in I'd be happy to bring it to the next SLAS meeting
The article I mentioned regarding the size of a scope's sweet spot was: Sinnott, Roger W. May 1991. Focus and Collimination: How Critical? Sky&Telescope pp528-531. Sinnott's equation for the diffraction limited field diameter for f/2 to f/10 scopes was - width_inches = 0.0007 * F^3 where F=focal ratio This works to the following for some common scopes at: In-focus sweet spot width F_ratio width_in width_mm %_1.25inFOV %_2inFOV 4 0.04 1 3 2 4.5 0.06 1 5 3 5 0.08 2 6 4 5.5 0.11 2 9 5 6 0.15 3 12 7 6.5 0.19 4 15 9 7 0.24 6 19 12 7.5 0.29 7 23 14 8 0.35 9 28 17 8.5 0.42 10 34 21 9 0.51 12 40 25 9.5 0.6 15 48 30 10 0.7 17 55 35 This also means that the fast mirrors scope have to be aligned within 1/10th of an inches or less or the image will degrade. Laser-aided collimation is a given. F/9 owners can drink heavily, horribly misalign their scopes by eyeballing and still have a passible image. -:) - Canopus56 __________________________________ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo