Can anyone explain how light really passes through a telescope???
Opinions I've heard seem contradictory so I'd appreciate some
clarification. In particular (and this is the practical reason for
asking the question) when light exits an eyepiece does it emerge as a
cylinder or as a cone? If a cone is it narrowing - i.e. focussed on a
point after the eyepiece - or is it diverging - i.e. already past the
point of focus?

My local telescope supplier tells me the light is converging but I
doubt the human eye could focus on that. My view is that the light
should emerge as a cylinder (i.e. appearing at infinity) of diameter up
to the size of the pupil of the eye and that the lens of the eye
focusses this on to the retina just as it would when viewing a distant
object. The counterexample he gave is of eye relief where the distance
from the eyepiece matters. I guess there is something in that so am
puzzled. Can anyone shed some light (sic, sorry) on this?


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Thanks,
James