Re: [ATM] RC with multiple primaries

[Ken Hunter <atm_ken_hunter@yahoo.com>]

For differing focal lengths you'll have differing
magnifications (angular field size) at the focal
plane. On axis stars would (could) be laid on top of
each other. Stars (point sources) off axis would show
a radial displacement for the differing focal length
elements.

You computer guys can figure out how much displacement
due to differing magnifications.

Ken Hunter


--- Jim Burrows <burrjaw@earthlink.net> wrote:

> At 2004-11-02 23:14 -0500, matt tudor wrote:
> 
> > >Matt: why do the primaries need to be identical
> to sub-wavelength accuracy?
> >
> >for the same reason all zones of a single piece
> primary mirror needs to have
> >a common focal length and not several. The multiple
> mirror is no different .
> 
> This is an interesting topic.  I think Matt is wrong
> here - the difference 
> between a segmented mirror and an ordinary mirror is
> that the segments can 
> be moved to correct for differing focal lengths
> (among other 
> errors).  Consider a perfect parabolic mirror
> surrounded by an annulus of 
> another perfect parabolic mirror with a different
> focal length.  Geometric 
> optics says that if you move the center mirror until
> the foci coincide, 
> you'll have a stigmatic mirror.  I won't hazard a
> guess what would happen 
> off-axis in this case <g>.
> 
>          -- Jim Burrows
>          -- mailto://burrjaw@earthlink.net
>          -- http://home.earthlink.net/~burrjaw
>          -- Seattle N47.4723 W122.3662 (WGS84) 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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