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

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

David Whysong wrote:

>
>For the secondary, I'm tentatively thinking 6" to fully illuminate a
>43mm circle (for 35mm format, in case I strike it rich and get an
>STL-11000M). The 21% obstruction is very acceptable. I could easily
>tolerate a larger secondary obstruction, for use with a focal reducer
>and large camera.
>
>I don't want to cut corners on this 'scope, though it would be okay to
>start with a binned ST-8XME/paracorr and try to construct a
>corrector/reducer as a later project.
>
>So, any comments, criticisms, or suggestions?
>
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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