Re: [ATM] OSC and doublets

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

Richard F.L.R. Snashall wrote:

 > Plugging this into the GSUM calculator and sliding the correction
 > wavelengths
 > up and down allowed me to get a version which has OSC accurately nulled:

Now that that has sunk in, I wanted to ask about a symptom I found
while finding these triple-point doublets (roughly: minimum focus,
nulled spherical aberration, and nulled coma).

I found these combinations by starting at some red wavelength for
both the minimum wavelength value and the center of correction and
then sliding the wavelength toward the blue until the OSC went to
zero.

What I found was that, pushing it further blue than that point
quickly led to a non-solution for the Gee Sum equations.  Typically
the amount needed to push it to a non-solution (the quadratic in C2 ==C3
that nulls longitudinal spherical aberration) -- the radical goes
negative.

The Gee Sum equations assume thin lens approximations.  The amount
that is needed to push it to a non-solution is small, mostly less
than one nanometer, so the extra may actually be zero in the limit.

Does any one have any reason to suspect that a solution that has
zero OSC will always be close to not having a solution for
longitudinal aberration? How about if you add the criterion that
the solution be at the minimum focus?  Does that even relate?

-- 

Rick S.

http://users.rcn.com/rflrs


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