Re: Incorrect Seidel aberration calculations in lens design codes

On Feb 22, 12:02 pm, Helpful person <rrl...@xxxxxxxxx> wrote:
It will effect the following lenses because it changes their
conjugates.  Remember that the Seidels are an approximation and have
never (even originally) been thought of as anything else.  The change
to the following individual lens Seidels is very small, smaller than
the Seidel approximation.

To my knowledge the second order terms are never considered.

Yes, the Seidels are a 4th order approximation to the wavefront
aberrations but should include ALL effects up to that order. The
contribution from the 2nd order term can be substantial when it nearly
cancels the curvature coefficent leading to a surface that is flat on
axis but with higher-order wiggle. In fact corrector plates in
Schmidt (or Wright or ...) telescopes can be modelled very accurately
by a conic surface with just an additional 2nd order term instead of
the usual much higher order expansion. For a discussion of this see:

http://www.breault.com/resources/kbasePDF/wp_osa_001_superconic_and.pdf

Al



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