Better Bak?

[Brian S]

Which is the better BAK rating for bino's 4 or 7?
Thanks
Brian

 

[Brian S]

I meant bk-7 I did a little search and found this:
BK7 & BAK-4 Prisms Inexpensive BK7 reflects a great deal of light causing a gray image blackout around the inside edge of the exit pupil... reducing light gathering. BAK4 prisms are top quality low reflectance glass for bright, clear, round, unreduced image.

 

[Spitzer]

Bak4 prisms with PC-3 phase coating is a plus.