I have a 5" four element refractor with a bad objective (asitgmatism). I have measured the curvature and density of the glass for each element. I would like to find a good shareware/freeware program that would let me back out the design. I could then (I hope) see if I could find a commercially available 5" objective that could be spaced correctly for this scope. Any help or suggestions would be appreciated.
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