Quote:
Originally Posted by JA
1. if it has 3 zero crossings on the focus v wavelength curve (3rd order cubic function) then it's a triplet and apochromat and
2. if it has 2 zero crossings on the focus v wavelength curve (2nd order parabolic function) then it's a doublet and achromat
3. if it has 4 zero crossings on the focus v wavelength curve (4th order quartic function) then it's a superachromat
So to answer your question: YES, NO and MAYBE  |
Well, again you are completely and utterly
wrong.
A doublet can easily have 3 zero crossings, and there are couple of glass combinations that will allow a doublet to have
FOUR zero crossings (see one of my posts above).
Yes,
apochromat or
superachromat can be done with just two lenses.