Re: [ATM] Aplanatic Schmidt-Cassegrains with aspherical mirrors

[Dominic-Luc Webb <dlwebb@canit.se>]

On Wed, 12 Jan 2005, Scott Ewart wrote:

>     Could the corrector in any way help correct field curvature by enabling
> a flatter curve somewhere else?  It doesn't sound like it.  It seems to me
> that's the one and only strike against an RC designed for photography for
> the masses.  What good are pin-point stars at the corner of the field if you
> can't focus on them, at least not without another corrector?  Unless they're
> coming out with a new curved ccd chip:)
>
> Scott


I would bet they are thinking more and more about this. My novice mind
thought of this long ago, and I even posted some comments about curved
CCDs long ago (years). That being said, consider the case for film
placed on a curved surface perfectly matched to the curvature at focus.
Having made these correctors, two interesting observations emerged.
First, the curvature is very slight. Second, the film is very thick.
One reaches a point in which it could be discussed where within the
thickness of the film one wants to focus. Before you go rushing off to
make a curved CCD or a curved film plate, see what is managable with a
flat surface. Most of the systems people in here are discussing end up
with only slightly curved focal surfaces, although, I have not been
following this thread to know the details of any specific design. I
suspect any transmission type corrector you try to make/add to this
system will add aberrations and you'll end up accepting the curved
surface as is.

Dominic-Luc Webb

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