Thanks, Bill. I suspected that the 32mm would be the practical limit for my
weary eyes.


----- Original Message -----
Sent: Saturday, May 19, 2001 12:19 AM
Subject: Re: [M]: Taking the plunge


>
> On Friday, May 18, 2001, at 08:05 PM, Michael De Santis wrote:
>
> > ... 10" LX200 f/6.3...
>
> > ...to figure out the exit pupil of various eyepiecs ...
>
> Divide the scope's aperture (254mm) by the magnification, which is in
> turn the ratio of the scope's focal length (1600mm) divided by the
> eyepiece's focal length. Thus a 12mm eyepiece gives a magnification of
> 133x which gives an exit pupil of 1.88mm.
>
> A little algebra will show that the exit pupil is also equal to the
> eyepiece's focal length divided by the scope's f/ ratio. Thus a 12mm
> eyepiece with your scope will give an exit pupil of just under 2mm.
>
> If you're old enough to afford such a nice scope it's unlikely that your
> eyes open more than about 5mm. Thus the lowest power eyepiece that's
> really useful is about 32mm (which gives about 50x). A 31mm Nagler Type
> 5 is just ticket :-)
>
> --
> Bill Arnett
> http://nineplanets.org/ 37 27 38 N 122 16 11 W
>

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