Re: [ATM] Ear of the Sow

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

Scott Milligan wrote:
> Richard:
>
> I don't know enough about the details of what residuals you are seeing in
> the (Schupmann) design you are looking at to make any certain judgments,
> however I can share from my own experience that a slight "tweak" of the
> field element position (tilt if mirror type, lateral translation if lens
> type) is often necessary to remove the small amount of lateral color at the
> field center that is introduced by the tilt/de-center that is in turn
> present to achieve an unobstructed beam path to and from the corrector.
Agreed.  Since these are spherical surfaces, a "small" wedge can be
handled as a lateral displacement.  In this instance, the sign of
that displacement is unfortunate -- it would require that an unused
portion of the smallest lens be sawn off so as to not stick into the
return beam from the final mirror.  The optimal position of the final
mirror seems to have elbow room:

    http://users.rcn.com/rflrs/Schupmann01-36x.len   OSLO input file
    http://users.rcn.com/rflrs/Schupmann01-36x.txt   TEXT prescription
    http://users.rcn.com/rflrs/Schupmann01-36x.zmx   ZEMAX input file

> Since different programs handle tilts and decenters differently, is it
> possible that this small adjustment has gone missing in the design that
> didn't trace "up to snuff"?
I have been generating a alternate design file in a form in which each
transformation/translation set is in Decenter-Tilt order.  When I
do that:

    http://users.rcn.com/rflrs/Schupmann01-36y.len   OSLO input file
    http://users.rcn.com/rflrs/Schupmann01-36y.txt   TEXT prescription
    http://users.rcn.com/rflrs/Schupmann01-36y.zmx   ZEMAX input file

Now, both OSLO and ZEMAX indicate a 5% change in the effective focal
length.  However, ZEMAX has the chromatic focal shift almost exactly
opposite to that in the unaltered format.  OSLO seems to indicate no
such difference.

As nearly as I can tell, the two geometric shapes are the same -- the
altered form generation process appears to  be correct.



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