BAK 6 prisms ??

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Barkley T Dog - 28 Apr 2005 21:53 GMT

I have noticed binoculars being advertised with the 'latest BAK 6 prisms'.
I've heard that BAK 4 are the best and BAK 7 are the most common, but has
anyone heard of BAK 6 and know if they are of good quality?

They seem to be of chinese manufacture, and i'm wondering if they are a
cheaper make of BAK 4's. (or is that wishful thinking)

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BC - 29 Apr 2005 02:15 GMT

> I have noticed binoculars being advertised with the 'latest BAK 6 prisms'.
> I've heard that BAK 4 are the best and BAK 7 are the most common, but has
> anyone heard of BAK 6 and know if they are of good quality?
>
> They seem to be of chinese manufacture, and i'm wondering if they are a
> cheaper make of BAK 4's. (or is that wishful thinking)

The only BAK6 I know of is made by Xinhu in China. It is equivalent to
Schott SK11, which has similar refractive index but lower dispersion
than Schott BAK4.

Brian
www.caldwellphotographic.com

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Bob May - 29 Apr 2005 21:04 GMT

All of those glasses are similar in their dispersion properties so the
differences will be very minimal for focusing of the light.
I'll note that binoculars are not very high power so the color error will
not be noticed even if BK-7 had been used. Light outut will be slightly
higher due to the better reflection of the light but that is quite minimal
in any case. A good anti-reflection coating will migitate such an increase
in light as will a better choice of glasses in the objective towards
reducing the color error.
BAK has a slightly higher index of refraction with a lower dispersion than
BK glasses so the dispersion of the colors will be lower in the BAK glasses.

--
Why isn't there an Ozone Hole at the NORTH Pole?

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Natural Science Forum / Physics / Optics / April 2005

BAK 6 prisms ??