Thanks, Joe. I wondered if the faster, shorter focal length systems of binoculars required having the ED element in the doublet, because that seems to be the standard arrangement in binoculars. However, if it could be done more cheaply in the EPs, it makes more sense to do that, but if so, why it isn't done?
Perhaps adding yet another optical element to a company's standard EP design requires that the other optical elements need to redesigned to accommodate the ED element, which could add costs rather than savings. Whereas with a doublet, they would only have to redesign one element to accommodate the ED glass. There's got to be some reason other than "if it ain't broke, don't fit it" that they always put the ED glass in the objective.
I also wonder if companies know that negative focusing elements increase CA, then why do they continue to use them instead of using positive focusing elements?
Brock