Re: ATM exit pupils

[Greg Granville <greg@laser.arl.psu.edu>]

> > Another possible factor at work:  at high powers Jupiter is less bright and
> > your pupil doesn't close down as much, so the eye pupil/diagonal shadow
> > problem is reduced or avoided?
> 
> The surface brightness will be decreased, but the total amount of light will
> remain the same as it depends only on the aperture of the scope.
> I expect that the entrance pupil of your eye depends on the total amount of
> light.

Yes, the total amount of light should remain about the same, but I'm not 100%
convinced that the human iris response is completly impervious to the surface
brightness of an object. I'd be willing to bet that it factors in along with the
total brightness of an object to a certain extent. It might be interesting so
see some real data on this.

> The pupil/diagonal shadow proplem thus should be worse in larger scopes.

I don't see the connection. As long as the exit pupil from the eyepiece is
smaller than the iris opening of the eye, the diagonal shadow will *always*
be exactly the same percentage (in relative size) of the exit pupil.
If the exit pupil size decreases in half, so does the size of the diagonal
shadow. 
Size of the scope should matter not - only thing that matters is
the exit pupil of the eyepiece and the dialated size of the iris of the
observer. So long as the later remains larger than the former, the effects
should be constant.

-- 
Greg Granville
greg@penn.com - greg@laser.arl.psu.edu
Visit the Central Pennsylvania Observers at:
http://users.penn.com/~greg/cpo.html