Re: Stupid question about magnification


William C. Keel wrote:

>
> What I think Cerdic was talking about is the possible use of a refractor
> with the human eye acting as the eyepiece as well as detector.

The eye has a serious problem in acting as an eyepiece: too small field
lens.
The closest it can get to any image with proper focus is ~250mm. So, in
order
to collect all the light from, say, 10mm diameter image produced by an
f/10 system,
it would have to have minimum 35mm clear diameter. With, say, 5mm pupil
opening,
it would only catch 4% of energy of the axial cone and not mor than
2-3mm of sufficiently illuminated field diameter. It would be much
worse with a fast system and smaller pupil.

Being close to the image, an eyepiece requires much smaller field lens
in order to efficiently handle diverging light cones.

Vlad

.

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