[ATM] Re: Aplantic Gregorian

[vladimir sacek <vladis.2@juno.com>]

Matt Tudor wrote:

>I am not sure what you call Mersenne as a
>complete system in your above email 

See my first response to you.

>and in what way would it be different
>than the 2 confocal paraboloids system which you seem to be referring as
a
>different thing ...

It's rather obvious: afocal reducer gives as a final output a bundle of
collimated
beams, while Mersenne telescope's final output is an image, formed after 
reflection of these collimated beams from the primary.

> Both of these are relatively fast mirrors unfortunately for analysis
>complexity , it seems . I can't tell if 3rd order aberrations analysis
is
>enough , I was looking for an analysis of higher order aberrations in
order
>to determine that .

Why the secrecy? You don't wan't to make it too easy on us? "Relatively
fast"
usually is not fast enough to make fifth order aberrations significant.
Even for 
fast systems, it is usually fifth order spherical that really needs
attention, and 
it is zero here, assuming proper mirror position.

I have one important correction to my previous post. It is in regard to 
size of off-axis aberration produced by using an imaging element 
(telescope) in a bundle of collimated beams produced by the afocal 
reducer. I assumed that the incident inclination angle for off-axis
points
remains unchanged after reflection from the secondary, which was wrong. 
It always gets larger after reflection from the secondary, and in the
case
of afocal reducer, the initial inclination angle "x" at the primary
becomes
x/k for collimated beams, "k" being the minimum secondary size in units
of 
the aperture.

In other words, for an imaging telescope which would use these collimated
beams to form an image, physical incident angle for all off-axis points
would be by a factor 1/k larger than that in a "direct" use. This would,
in general, increase its inherent coma by a factor 1/k, and its inherent
astigmatism by a factor 1/k^2 (increase in astigmatism would also
wosen curvature of the field of best definition).

In light of this, it seems reasonable to expect that most configurations
would give only a narrow angular field of good definition.

Vlad
_______________________________________________
ATM mailing list http://www.atmlist.net/