On 7 Jan 2007 08:11:20 -0800, "Chuck Gould"
wrote:

Both are are 7 power magnification with a 50mm diameter objective lens.
Both will magnify the image the same amount, and should gather about
the same amount of light.

I'm told, but have no direct personal knowledge, that lens coatings
have a great deal to with effective light gathering power. Supposedly
the German U-boat commanders at the beginning of WW II had 7 x 50
binocs and periscopes with superior coatings that gave them a huge
advantage at night.

from Hans Seeger, Militaerische Fernglaeser und Fernrohre
[page 331]
===
In 1935/36, Alexander Smakula (Zeiss, Jena) developed the
lens coating, a reflection reducing coating for optical elements. For
all optics, especially thoise with numerous surfaces, the coating
(also called 'blue coating') is a valuable means to increase the
transparency and therefore the brightness of the image. In marine
optics, the coating was especially useful. U-boat periscope optics
were the first to receive this new coating, along with the Navy field
glasses. In Germany, Navy optics and tank aiming field glasses were
the only items manufactured with coated optics; and other German
military models usually didn't have coating (and when it is there,
that nearly always means it was applied later, and the original
condition is falsified.)
===

http://en.wikipedia.org/wiki/Binocul...tical_coatings

The reason that 7 x 50s in general are superior, is that particular
combination of optics yields an exit beam width equal to the fully
dilated diameter of the pupils in your eye.

http://en.wikipedia.org/wiki/Exit_pupil