Re: [ATM] Turned Down Edge

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-07-14 21:08 -0400, Michael Lindner wrote:

>Jim, I think you misunderstood my intent. If you deepen the center, the
>difference in focal length between center and edge increases. Relative to a
>best fit curve, the edge appears to turn down "by magic" (e.g. without being
>touched by the lap). Yes, you can change the curve to one that isn't a best
>fit, but you're still moving towards hyperbola land in reality, becoming more
>and more frustrated as the edge continues to "turn" while you're avoiding it.
>
>This IMHO is why TDE is such a big bugaboo. TUE is easy to fix. You put the
>lap on it and it comes down. TDE will not come down if you avoid the edge.

Mike,

I guess you're right.  I put a TDE on Texereau's standard 8"f/6, 0 to -200 
nm from 90 to 100 mm getting .485 Strehl (attached tde.jpg, vs. best-fit, 
Bfit_tde.jpg).  I couldn't improve the Strehl by just digging holes in the 
center without, as you say, touching the edge.

If we go halfway, lower all the center 0 - 90 mm by 100 nm, but also work 
the TDE a little - change its slope so that it now goes from -100 to -200 
nm (you could do this, I guess, with a 180 mm diameter small tool stroking 
just to the edge: fix.jpg) Eureka! passing with .835 Strehl!

I'll send this to the list without the figures.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84)  

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