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

[Michael Peck <mpeck1@ix.netcom.com>]

At 06:13 10/15/05, David Whysong wrote:

>SURFACE RADIUS          THICKNESS       APERTURE RADIUS GLASS   SPECIAL
>OBJ     --              5.6743e+19      8.4186e+17      AIR
>
>AST     -5.8830e+3      -2.7197e+03     361.897150 A    REFLECT *
>2       -320.748335 V   -6.878973       70.000000       BK7     C
>3       -202.021812 V   -70.677574      70.000000       AIR
>4       -310.258760 V   -14.475886      65.000000       F6      C
>5       4.3789e+03  V   -50.665601      65.000000       AIR
>6       -443.950052 V   -18.094858      53.000000       BK7     C
>7       1.7508e+03  V    -5.066560      53.000000       SF11    C
>8       -144.758860 V   -14.475886      53.000000       LAFN28  C
>9       -2.8344e+03 V   -49.830000      53.000000       AIR
>10      --              --              36.000000       BK7     C
>11      --              --              36.000000       AIR
>IMS     --              -0.001395       35.780712 S
>
>(I don't understand why the size of the primary is 28.4" rather than 1
>meter - this differs from the other examples in the paper. And I don't
>understand surfaces #10 and #11; I guess that just defines the focal
>plane.)

Are you sure this is specified right? As shown this has a BK7 window 
of zero thickness, which obviously would perform no optical function. 
In OSLO putting a dummy surface at the Gaussian focus will make it 
extend ray diagrams to the focal plane - otherwise they get truncated 
just past the last real surface. That's the only purpose for surface 
11 as far as I know.

If I entered this design correctly it looks not so good to me. It's 
producing geometric spot sizes around 20 microns and is short of 
diffraction limited by about an order of magnitude.

Go to the searchable ATM list archives at 
<http://astro.umsystem.edu/atm/search.html> and try a search on 
"hyperbolic astrograph". If the primary can be made somewhat 
hyperboloidal a much simpler field corrector can be designed. In fact 
Dave Rowe posted one for a similar sized telescope just a couple months ago.

As for focal reduction, why not save for a larger format camera instead?



_________________

Michael Peck
email mpeck1@ix.netcom.com
Wildlife photoblog! http://wildlife-pix.com
Amateur telescope making http://home.earthlink.net/~mlpeck54/astro/astro.html 

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