Graywolf wrote: > The opposite. High (or Extra, or Extreme) dispersion glass requires less > curvature to obtain the same dioter. In a prism the colors would be > spread farther.
Indeed. If it was Extra low dispersion, then the initials would be ELD. Manufacturers wouldn't miss the opportunity to stick _another_ letter into a lens designation - except, maybe, Pentax.
Bending the light more allows one to build smaller optics. It also, as noted, creates other problems....
I'm beginning to wonder if people are confusing dispersion and refraction. They are not the same thing.
I thought the point of glasses like Pentax ED was that they had lower dispersion for a given degree of refraction than older glasses (or conversely extra diffraction for a given level of dispersion.)
Cheers, Eric.
