Quote:
Originally Posted by bratislav
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.
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Good I like that . Always a chance to learn, but just so we're clear when was the last time I was completely and utterly wrong (since you didn't mention it previously)?
In any event read carefully what I said rather than partially quote it to attempt to make a point. One can hardly be "completely and utterly wrong"
when one prefaces one's comments with
Quote:
Originally Posted by JA
Well it really depends on how exactly or inexactly one cares to define an apochromat:
Is it defined by
1. the number of lenses in the design or
2. by how well it corrects for aberration (typically spherical and chromatic) ?
Some would say that
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
Others simply say that the apochromat corrects better than the achromat and leave that as some sort of definition.
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Just in case you missed it I was demonstrating two opposing points of view. I thought that would have been clear and that it didn't need further explanation.
So please now join in the conversation and answer Jeremy's original question, instead of relying on the crumbs from someone who tries to. EDIT: My apologies, I just noticed you did now answer his question- Well done. Now that wasn't too hard was it?
XXX
Best
JA