Re: ATM Off axis parabolas

[Bratislav Curcic <epabcc@epa.ericsson.se>]

Kurt wrote :

>  But the aberrations of the optics (coma, etc.) are pretty much
> the same ;

Maybe in linear terms, but let's not forget that effective f/ratio
_does_ increase at least twofolds; the Airy disk of the masked scope is
at least 2 times larger (in reality closer to 3 times). Consequently
the "diffraction limited" area is increased. Also, the eyepieces can be
made to work better by tilting them somewhat (say half way between the
optical center of the mirror and the physical center of the "working"
area). This way eyepiece will see beam that is much less steep; in the
example above, instead of f/2.5 horror (I don't know of ANY eyepiece
that would work well at that), it would be something much more acceptable,
like ~f/4.

Bratislav