Re: [ATM] Another flat-field anastigmatic aplant

["vladimir" <svla@isp.com>]

Ukyo Chen wrote:


> Centre hole will be a big problem(around 40% D) if you want to avoid 
> vignetting.

40% and larger c.obscuration are quite usual for photographic systems

> Adjust will be a difficulit job for 3-mirror systems(4 mirrors with a 
> diagonal)

No news...

> You will lost more light when put a diagonal into split light pole compare 
> with parallel light pole.

Again, no more than usual.

> 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
>

That is similar to Paul-Baker variety, which can be made to be flat-field
w/o need for corrector.
The general parameters are quite simple; they've been posted recently, but
I'll do it again:

K1: -1
R1: unit
to secondary : [(1-k)R1]/2 = R3
K2: -1+(1-k)^3
R2: kR1
to tertiary:  kR1/(1-k)
K3: 0

with "k" being the hight of marginal ray at the secondary, which can be
expressed as

k=1-(s/f), "s" being the primary-to-secondary separation, and "f" the
primaty f.l.

Such system is a flat-field anastigmatic aplant. It does requires larger
mirrors and c.obscuration
than the arrangement I posted, but it also has a potential for significantly
wider field available.
However, in the range of smaller (amateurs') apertures, that advantage may
not be very significant.

Vlad

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