Re: Galileo's telescope's f-ratio
From: Jeroen Smaal (jsnews_at_REMOVE-THIS.zippy.xs4all.nl)
Date: 10/27/04
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Date: Wed, 27 Oct 2004 20:49:21 +0200
"Jud McCranie" <youknowwhat.mccranie@adelphia.net> wrote in message
news:aqotn01pfc2vkm4mtg0e096s8efoq9748l@4ax.com...
> Galileo's 14x telescope had a focal length of 1330mm with an aperture
> of 26mm, giving an f ratio of f/51. Would that be pretty dim?
> http://outreach.atnf.csiro.au/education/senior/astrophysics/galileo.html#galtelescope
> ---
> Replace you know what by j to email
Hi,
It would have had an exit pupil of (26/14) = 1.8mm. Not ideal, but bright
enough for observing the planets I suppose.
Actually, for a magnification of 14x, it has to have had an eyepiece
equivalent with a focal length of 95mm. The long focal ratio would have been
needed to offset the effects of the crude optics of that time.
jeroen.
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