From: "mommoteandcoyote" 
To: "Jerry Hudson" 
Cc: 
Reply-To: "mommoteandcoyote" 


Jerry,

Ah, a graphical approach, a little more up my alley, I think.

Ya, before Edgar Everhart and his article in Applied Optics in 1966, and
Bob Cox bringing it to everyone's attention in 7/72 "Gleanings", 
there wasn't much on vacuum *plate generation*, save what we had in ATM
III.

Thanks Jerry.
Come on over...

Talk with you soon,
Coyot‚


----- Original Message -----
From: "Jerry Hudson" 
To: 
Sent: Wednesday, January 22, 2003 12:16 PM Subject: Re:ATM An Old TMs Simple Query


>
> To ol' Coyote -
>
> Your formula,
> >  a*rho^2+b*rho^+b*rho^4...
> giving the shape of the Schmidt plate, is
> exactly opposite in sign to the wavefront
> aberration describing an uncorrected spherical
> mirror.  The glass introduces just enough extra
> path length where it is thicker to compensate.
>
> A straightforward way to see how this all works
> out, if you have the patience and either a
> good calculator or BASIC, is to start
> at the desired focal point of the sphere and
> trace a ray, bouncing it off the sphere, and
> taking it out to where it intersects a plane
> positioned where you want the plate to go.
> Figure out the path distance along that ray,
> and subtract off the path distance for the
> central ray.  THat's your "wavefront aberration."
> If you plot this against radial distance of
> the ray from the axis, you will get a 4th order
> looking curve.
>
> Note that adding the rho^2 term simply re-focuses
> the wavefront - you have this degree of freedom
> to try to make the overall power of the plate
> to be zero (avoiding all but a trace of color).
>
> I hope this helps.
>
> BTW, I'd enjoy a direct off-list exchange with
> you about Schmidts - an interest of mine.  I've
> only made one: a Wright-type Newtonian.  And, yes,
> Edgar Everhart's articles were a great help to me!
> He was a smart guy and a great glass-pusher!
>
> - Jerry Hudson
>
>
>
>

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