Re: [ATM] Another flat-field anastigmatic aplant

["Ukyo Chen" <ukyochen888@hotmail.com>]

Centre hole will be a big problem(around 40% D) if you want to avoid 
vignetting.
Adjust will be a difficulit job for 3-mirror systems(4 mirrors with a 
diagonal)
You will lost more light when put a diagonal into split light pole compare 
with parallel light pole.

With similar contre hole, another 3-mirror system is better as it reachs to 
faster F number, like F/3.
Please check my work here:
http://www.astron.sh.cn/cgi-bin/attachment.cgi?forum=2&topic=1617&postno=10&type=.gif

Best Regards,
Ukyo Chen

>From: "vladimir" <svla@isp.com>
>To: <atm@atmlist.net>
>Subject: [ATM] Another flat-field anastigmatic aplant
>Date: Sat, 17 Dec 2005 11:06:16 -0500
>
>I touched this system before, but it didn't seem really workable.
>But then, it may be. It is a 3-mirror system, consisting from
>a concave ellipsoidal primary, convex spherical secondary
>placed inside the primary focus, refocusing in the primary/secondary
>interspace and sending diverging beam through opening on the primary to the 
>ellipsoidal tertiary
>that forms final image behind the primary. The final image can be made 
>accessible
>with a diagonal flat.
>
>The arrangement is quite similar to Willstrop's variant of Paul-Baker in 
>mirror placement.
>The mirrors are somewhat easier to make, baffling is inherently easier due 
>to configuration,
>but it also puts limit of somewhat over 1 degree diameter to the field 
>w/acceptable edge vignetting
>and up to ~50% c.obstruction.
>
>An example is this 400mm aperture f/4.56 system:
>R1=-2400mm
>K1=-0.742
>to secondary:-1017.5mm
>R2=-550mm
>K2=0
>to tertiary:1600mm
>R3=-713.5mm
>K3=-0.373
>
>Arrangement can have smaller or larger secondary/tertiary sets. The smaller 
>they get,
>the more aspherising needed for the primary and tertiary (they remain 
>ellipsoids). The system f#
>is nearly fixed in terms of primary's f#, being approximately 1.5 times 
>"slower".
>
>The flat-field Strehl .5 degree (16mm) off-axis is 0.995 for the above 
>system.
>
>Vlad
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