ATM Re: All Sky Instrument

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

John D. Gwinner wrote :

> They want LOW F ratio; say F2 or F1.4. ...  no curved focal plane
>   What would be the best optical design for that?

Probably a Schwarzschild or a Couder (a two mirror telescope
with two concave mirrors and a internal foucus; i.e. foucus
between the mirrors) or Schwarzschild-Wynn (a weird looking
scope with a CONVEX primary, also with flat field). None of these
can really reach f/1.4, that is realm of Schmidts and Maksutov
cameras (and clones e.g. Baker, solid Schmidt etc.).

>   A few people have suggested removing the secondary on a commercial
> (Meade) schmidt camera and converting to prime focus CCD imaging.  

1. there is no secondary in a schmidt camera
2. if sugeestion was about removing secondary in a commercial SCT,
   the bad news is that curvature of the field stays more or less the
   same as in an equivalent Schmidt (quite severe as primary is around
   f/2 in commercial SCTs)

Another possibility is to make an apochromatic distant field flattener
for Schmidt. If we can afford to have lens in contact with CCD chip,
the requirement for apochromatism can be lessened a bit. 

Bratislav