Re: [ATM] Another flat-field anastigmatic aplant

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

vladimir wrote:

>Richard F.L.R. Snashall wrote:
>
>
>>Now, if I've done everything right, this one may work.  I don't
>>know if anyone will like the geometry...
>>
>
>So, it could go down to c.obstruction ~D/3 vs.
>somewhat over 0.4D in the shorter version. Still great field quality, 
>but the tertiary is just too far back. Even the photons would go: 
>"Man, that's a long walk..."
>
Can't argue there.  It can get worse, though.  In:

Surf      Radius      Thickness      Diameter          Conic

 STO    Infinity       8.631515           400              0
   2    -2318.88       -892.222           400     -0.5853937  primary
   3   -875.4511        892.222      107.7176              0  secondary
   4    -2318.88       754.3033      92.14499     -0.5853937  central hole
   5    Infinity       875.1653      234.4802              0  
(quaternary point)
   6    -1391.18      -875.1653      396.8431     -0.2732093  tertiary
   7    Infinity      -244.8145      63.14406              0  quaternary
 IMA    Infinity                     31.74363              0  image

the central hole is made smaller than the secondary to roughly
allow for the 0.5 degree shadow cone angle from the secondary.
The quaternary (diagonal) is adjusted in position so that its
minor diameter compared to the diameter of the secondary-tertiary
cone at that point is equal to the ratio of the secondary to the
primary -- again, some sort of "optimality".

It works out well at this f/# with the image plane further away
from the axis than the semi-aperture, and the CO being roughly
only 27%.

But, being that far behind the primary, the tertiary is nearly
as large as it.

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