From: "John Sherman" 
To: 
Reply-To: "John Sherman" 






>
> hi John

Hi to you too, Nils Olof,

> magnification is the aperture divided by the exit pupil,

True. The magnification of a telescope is the entrance pupil divided by the
exit pupil.

> With a low-f/# telescope, the diffraction pattern at the focal plane
> is indeed smaller - so that's why you need a shorter f-l eyepiece to
> magnify it more!

True.

I know that a telescope makes a diffraction pattern from a star. With a low
power eyepiece, it appears small. With a medium power, it is larger; with a
high power eyepiece it is larger still. So in that respect the
"apparent size" of the diffraction disc is dependent on the
eyepiece used, and the magnification provided. However, in each eyepiece
the whole field gets magnified, and so the disc still subtends the same
angle on the sky. As was pointed out, that angle is 2.44 lambda/D, usually
given in arc-seconds. It is not dependent on the magnification, or even the
f/#.

Why not??


> Hope this helps (there's always hope)

Thanks for hoping!

John

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