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

["matt" <mariusrf@bellsouth.net>]

That dealer probably couldn't tell the difference between a hyperbola and a
parabola and wouldn't know what conic constant is anyway .
I wouldn't be surprised if in the end, these scopes turn out to have a
hyperbolic secondary with a spherical primary and a corrector plate that
makes the corrector+primary look hyperbolic . Or the primary is slightly
aspheric but not quite the required hyperbola for an RC and the corrector
compensates for the remainder. While these wouldn't reach the performance
level of a true R-C , they would be way better than the current all
spherical SCT's Meade is selling .
A large optically flat robust enough plate to support the secondary is much
more expensive than a spider . Not to mention it transmits less light than
the spider version , even with Meade's high UHTC claims there are 2 extra
air to glass surfaces . Expensive and there for no reason ? Seems strange
from a company that is well known for cutting corners to all of a sudden
waste money on such an expensive part without having a need for it .

best regards,
matt tudor

> ----- Original Message -----
> From: "Michael Peck" <mpeck1@ix.netcom.com>
> To: <atm@atmlist.net>
> Sent: Wednesday, January 12, 2005 10:53 AM
> Subject: Re: [ATM] Aplanatic Schmidt-Cassegrains with aspherical mirrors
>
>
>
>  The geometry determines field curvature, so you can't do
> anything about that and you don't care about distortion.
>
>  On one of
> the Yahoo chat groups that sprang up to hype these things a dealer who
> probably knows more than he's allowed to say assured me that their new
line
> of Ritchey-Chretiens *do* have two hyperboloidal mirrors. Since that's a
> readily verifiable fact (at least when they become available to people who
> aren't constrained by nondisclosure agreements) I have to assume he's
> telling the truth. That means they're true RC designs. The one thing that
> still puzzles me a bit is that if the mirrors have the conics of an RC the
> corrector plate has nothing to do except hold the secondary assembly.
> That's fine if you don't mind having a thin piece of glass at the front
end
> of your telescope, but they also claim to be using it to "minimize"
> astigmatism. The only way I see to affect astigmatism given two
> hyperboloidal mirrors is to tweak the conics of the mirrors a little bit
> and add some correction to the corrector. That will affect the astigmatism
> a little bit in the right direction, but only to a very limited extent.
>
> Mike Peck
>
>
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>

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