[ATM] Binocular prism glass

[Mark Holm <mdholm@telerama.com>]

I was reading claims in the Orion catalog and got to wondering about one 
of them.  They claim that "high index" BAK-4 prisms are superior in 
binoculars to BK-7 prisms.  Does anybody know if this should be true.  
Seems to me, there might be good arguments for low index and the lower 
dispersion that usually goes with it.

I guess I don't really know a whole lot about binocular prisms, and 
would like to know a little bit more, if some one of you wise atm's has 
knowledge to share.  For my current purpose you could probably stick 
with the old fashioned prisms (aren't they "Porro") and skip the 
newfangled roof prisms.

Mark Holm
mdholm@telerama.com

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