Re: [ATM] Ear of the Sow

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

Bob May wrote:
>
> For a Schupmann, I'd probably do one with the reallly cheap K5
> glass.  Anybody for a forty inch or larger Schupmann?  Make the
> biggest refractor in the world and get excellent color correction
> to boot.
I didn't do one for K5, but I did try to get real cheap and see wha
I could do with some half-inch Optiwhite (thanks to the RI data
provided by Dominic-Luc Webb!). This time, more or less purely over
the visual band:

    http://users.rcn.com/rflrs/Schupmann01-27y.len   OSLO input file

The three lenses here can be made about 130, 18 and 80 mm in diameter;
there isn't much room to pass the light by the middle lens on its
way to the focal surface, so that will be tight.  BTW, does anybody
who deals with, Yolo's and Schliefspiegelers use an achromatic wedge
to bring the focal surface back to roughly perpendicular to the light?
But, the hard part will, I think, may still be the construction of the
two smaller lenses with non-zero wedge.

The problem here is, on top of my own difficulties visualizing things
three-dimensionally,  I'm not sure I know which, if any, of the
ZEMAX or OSLO output I can believe.  The original (20 surface) model
in ZEMAX indicates 34 micron longitudinal color error over g to r;
but, when I try to reduce it to the export (10 surface) it mushrooms
to several hundred microns; when I import it into OSLO (with all the
tweaks that that entails), I'm back to about 50 microns; but both
ZEMAX and OSLO indicate a focal length change of 26 mm in 1000 --
seems like a lot, given I put all distances in to the nanometer and
angles to microdegrees.


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