Re: binocular glass number?

alishadevoc...@xxxxxxxxx wrote:
Last year I was looking at some binocular and one of them listed that
it has high end glass -- something called military glass number?

Anyone know what to look for in binocular?

It depends on what you want in a binocular.

A plain, ordinary binocular should be 7x50 instead of, say, 8x30, it
might be recommended here - that's because 50 is not much more than
seven times the first number, the 7. This means the magnification is
not high enough to make the sky less bright.

If you are interested in getting a good quality binocular, first you
should determine how well-known and reputable the brand is. Then,
other claims about features can be considered.

Image stabilization is interesting, but expensive.

Lanthanum glass is a glass that is somewhat better than ordinary
glasses, since it can have a higher refractive index with less
dispersion. This means less chromatic aberration and less spherical
aberration. It is used to make long eye-relief eyepieces, but it can
be used to improve many optical systems.

A more elaborate kind of glass resembles the mineral fluorite. It
therefore disperses color in a different way than crown and flint
glasses, and can be combined with them to create apochromatic lenses.

Even more elaborate is the new ED glass, which lets one make two-
element lenses the chromatic aberration of which is nearly as low as
that of traditional three-element apochromats.

John Savard

.

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