Re: Eye vs Eyepiece focal ratio

On Nov 29, 12:53 am, Mus <musec...@xxxxxxxxx> wrote:
Hi,

Our eyes are said to have a focal ratio of 3 (F/3). Is there any
effect if the eyepiece focal ratio is also F/3 and not F/3? What
is the focal ratio of typical eyepieces like the Televue 9mm Plossl
or 20mm Plossl?

Thanks.

Mus

Of course, when the eye's pupil constricts, the eye's focal ratio
increases. It seems that the effective focal ratio of an eyepiece is
equal to the effective focal ratio of the objective. If the eye's
pupil becomes smaller than the telescope's exit pupil, then the
effective focal ratio of both the objective and the eyepiece
increase. If you are talking about the ratio of the eyepiece's focal
length to the eyepiece's clear aperture I would guesstimate that a
Plossl is somewhat slower than about f/1.2, and a Huygens eyepiece
maybe slower than f/4.


.

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