Re: ATM Unobstructed Optics Viewing

[epabcc@epa.ericsson.se (Bratislav Curcic)]

Steve Lee wrote :

> Horace Dall used an iris in his eyepieces as an aperture stop
> If placed in the right position, such an iris IS EXACTLY THE SAME as
> an aperture stop on the mirror.  This is how camera lens aperture stops
> work, I believe. 

Unfortunately, there is NO such position for Newtonian. Basically you
can use iris wherever you have image of the objective formed. In case
of Dall Kirkham (especialy with a relay lens) it's easy. With Newtonian
you can either place it on a mirror, or behind eyepiece (right at exit
pupil). The second option is not very practical of course, because you'll
need different apertures for different magnifications. And with short
f.l. eyepieces (that presumably are going to be used on planets anyway),
you'll have trouble placing your eye close enough.

Bratislav