Re: [ATM] Corrector/reducer for a fast Newtonian

[David Whysong <dwhysong@gmail.com>]

Thanks! This is nifty. I re-optimized that design to fit my nominal
primary mirror parameters, and got this:

 SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  SPE  NOTE
 OBJ       --        1.0000e+20    7.8541e+17             AIR

 AST  -5.2324e+03   -2.3123e+03 V  354.076000 A    REFL_HATCH   *

  2   -109.711559 V  -10.000000     60.186668 S         N-BK7 C
  3   -153.257323 V  -54.340062 V   57.457552 S           AIR

  4   -245.449338 V   -6.000000     45.491903 S         N-BK7 C
  5    -89.440217 V -204.292329 V   44.241967 S           AIR

  6   -180.083280 V   -7.000000     31.913633 S         N-BK7 C
  7    1.2276e+07 V   -3.500000     31.212471 S            F2 C
  8        --        -50.000000     30.884232 S           AIR

 IMS       --            --         23.291521 S

Performance is decent but not spectacular (even on-axis), but the spot
diagram is roughly diffraction limited out to the 0.7 zone, and
perhaps 20 microns or so at the edge of a 0.9 degree (dia.) field.
This might be useable so long as the fabrication tolerances aren't
impossible. And I haven't even tried to adjust the lens thicknesses
yet...

Does the spot diagram look decent to anyone else?

I'm still looking at the Paul-Baker design, and I really like it! And
even better, they can be made in extremely short focal ratios. But it
seems limited by having the focal plane inside the telescope; the
camera must be small enough so as to fit in the (reduced) shadow of
the secondary, and not cause further obstruction. This may make the
design impractical for all but the very largest (perhaps meter-class)
amateur telescopes. Am I missing something?

Well, that, and who can figure a large paraboloid below f/3?

--
David Whysong
Astrophysics Group
University of California, Santa Barbara


On 10/19/05, Richard F.L.R. Snashall <rflrs@rcn.com> wrote:
> With your reduced requirements, maybe you could do it with a
> combination of some sort:
>
>  SRF      RADIUS      THICKNESS   APERTURE RADIUS       GLASS  SPE  NOTE
>  OBJ       --        1.0000e+20    6.5451e+17             AIR
>
>  AST  -5.8830e+03   -2.6557e+03    361.807819 A       REFLECT   *
>
>   2   -108.064247    -10.000000     54.000000           N-BK7 C
>   3   -144.821970    -57.872932     54.000000             AIR
>
>   4   -234.621924     -6.000000     42.000000           N-BK7 C
>   5    -86.783062   -177.981536     42.000000             AIR
>
>   6   -163.374677     -7.000000     32.000000           N-BK7 C
>   7    3.4229e+03     -3.500000     32.000000              F2 C
>   8        --        -50.000000     32.000000             AIR
>
>  IMS       --            --         21.640736
>
>
> The spots across the h-t band aren't round, but they may be
> reasonably enough small to compensate for it.  Of course, the
> focal length is actually larger than the primary focal length
> instead of smaller, so that could be a problem.  If need be,
> the design would actually improve a bit if the last space
> were adjusted to fit a standard 35 mm camera body (55 mm plus
> mount space, IIRC).
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