From: Aplanatic{at}aol.com
To: atm{at}shore.net
Reply-To: Aplanatic{at}aol.com


Hello ol' Coyote,

I'm not quite sure what you're asking.  Here's a spreadsheet that does the
vacpan calculations for you:

http://members.aol.com/aplanatic/vacpan.xls

The aspheric function, z = a*rho^2 + b*rho^4 + ...

is just a way to describe the surface height (or corrector thickness), z,
as a function of the radial distance from the center of the corrector, rho.
 The coefficients, a, b, c,... are selected to make the best corrector
possible for a given optical problem.

'b' is called the fourth-order coefficient and it (loosely) governs the amount
of spherical aberration that is introduced by the corrector.  This
spherical aberration (SA) cancels the SA introduced by the other optical
components in the system.

'a' is called the second-order coefficient and it (loosely) governs the optical
power of the corrector.  It is choosen so that the corrector has minimum
chromatic aberration, which typically places the neutral zone at about 80%.

-Dave-




> I have asked a few of the guys, on the side, this question...Well, now I'm
putting it before the board. (Gulp), Here goes...
>
> I have been building small Schmidt systems for many years now, configured as
prime focus cameras, visual Newtonians, and  photo/visual Cassegrains.
Primarily, I've been using Everhart's variation of "Grandpa"
Bernard's vacuum pan method for producing the corrector plates, with very
good results.  His math was, and still is, quite easy for me to understand
and relate to the actual physical, quantifiable, and mechanical functions
necessary to produce the desired optical effect upon the system as a whole.
  However, in all the
years of walkin' around the bench and holding my eye precariously close to
a very sharp object, peering earnestly, hour upon hour, past a little spot
of light, I have never been able to grasp the basics of the polynomial
equations necessary to describe the specific profile on a specific
corrector plate and how it actually relates to the plate.  You know, the
old
>
>  a*rho^2+b*rho^+b*rho^4...
>
>  The coefficients of the even aspheric I think is what it's called.  How does
this become the 3 expressions that are used  when referring to a specific
plate, AND WHAT ARE *THEY* WITH REFERENCE TO THE PLATE?  Call me dense...
Call me 'tupid... But over my head it goes...     In any case, these and
other
related equations plum stump the ol' Coyote.  I can create the proper
curves on the glass at the bench, but I'll be damned if I can figure it out
mathematically so I can enter it
> into a computer program.  Chuckle, chuckle,
>  chuckle!
>
>  Any help you all can lend would be GREATLY appreciated! "
>
>
>
> Talk with you soon,
> Coyot‚

--- BBBS/NT v4.00 MP