To: atm{at}shore.net
From: "Stephen C. Koehler" 
Reply-To: "Stephen C. Koehler" 



John,

> > The angular size of the Airy disk depends only on D.  I would assert that
> > this is the more important relationship, because it determines the angular
> > resolution of the telescope.
>
> Ooh, you're hurting my head. Okay, so the angular resolution of the
> telescope is dependent on the aperture. But how can that have anything to do
> with the size of the Airy disc, if the size of the Airy disc is dependent on
> the F/#? It seems to me that if the angular resolving power of the scope is
> dependent on the Airy disc size, then the angular resolving power is also
> dependent on the F/#.

Michael Lindner explained it very well.

Let me give a more qualitative answer. The angular size of the Airy disk
(inversely related to D) is how much of the sky it takes up in the eyepiece
(e.g., the image of a star as seen in a telescope is an Airy disk with
diameter of 1 arcsecond).  The linear size of the Airy disk (inversely
related to F/D) is how large it is in the image formed at the focal
plane--you can get out a ruler and measure it.

> Is this somehow tied to the magnification of the scope plus
> eyepiece plus eyeball combination?

Both of these are properties of the objective only.  The eyepiece allows
you to look closer at the image in the focal plane, and the focal length of
the eyepiece determines how big the Airy disk looks to you.

--
Steve Koehler
koehler{at}securecomputing.com

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