Re: [ATM] Corrector/reducer for a fast Newtonian

["vladimir" <svla@isp.com>]

If it is to be primarily imaging instrument, why not
consider a two-mirror corrector (Paul-Baker)?
With little ingenuity, a structure could be made 
to accomodate either the two PB spherical mirrors
or, for relatively rare occasions, regular Newtonian
diagonal/focuser.

A PB system with an  f/3.67 paraboloidal primary
would have nearly identical F#. With, say, 0.25D min
secondary size and D=28", the system would look like:

R1=-205.52"
K1=-1
primary-to-secondary: 77.07"
R2=-52.05"
K2=0
secondary-to-tertiary: 52.05"
R3=-52.05"
K3=0

Note that secondary/tertiary radius and separation are 
slightly longer than what would be required for confocal
primary/secondary (51.97"). This is to optimize for higher
order spherical, although confocal arrangement would
have indistinguishable performance with slight refocusing.
Flat field blur 21.5mm off-axis is 23um, coming from
the -2600mm field curvature. On the optimum surface,
the spot is of sub-micron diameter across the field
(-0.993 Strehl 21.5mm off-axis).

C.obstruction would probably have to be ~40%, or
somewhat larger, to ensure good baffling.

Vlad

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