From: "Jim Van Nuland" <jvn@No-Spam>
Subject: Re: [TAC] re: 58mm Plossl question
> ...I know someone whose dark-adapted pupil
> was 10 millimeters, but that's rare.
Then that uppity Claytor dude done went n wrote:
>Yeah, I know that guy. His name is LaFlamme.
I wish! I sold a 41 Panoptic because I noticed that M31 looked washed out
when using it with my 15 f/5. A 31 Nagler really helped to separate the
lanes and showed more detail with a similar F.O.V. albeit with a slight
increase of magnification. Much better yes, but why? I learned about "exit
pupil" and how to calculate it. Turns out that in my 15" f/5 the 41 Pan was
giving me an exit pupil of 8.2mm! Much too large for my eyes but the 31
Nagler with its similar F.O.V. cut that number down to 6.2! The exit pupil
for a given eyepiece is totally dependent on the scope you plug it into. So,
to calculate the exit pupil of your own eyepieces/scope simply divide the FL
of your eyepiece by the FL of you telescope. In my case 31 divided by 5 =
6.2. I now own a 26 Nagler (5.2mm exit pupil) and consider 6mm to be the
largest exit pupil that I will use with any of my scopes. I don't use my
large Newtonian for wide fields anyway, a degree or less is fine. I hunt
faint fuzz mainly so I work at high powers with exit pupils in the 1-3mm
range. I love Jamie's quick and dirty math formula for figuring out what
eyepiece may be too much for given instrument. 7 is probably a good number
for younger folks, 6 may be more realistic and at 40 years of age, that's
the number I settled on for now.
GML
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Received on Wed Aug 27 16:38:16 2008
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