Quick Question

[joggerman]

How can the Helios Stellar II 20 x 100 have a FOV of 3.2 yet the Skymaster 20x80 has FOV of 3.7 ?
I thought it woukld be the other way round ???

[Voyageur]

Field of view depends on the optical design of the eyepieces, not the aperture of the objective lenses.

Larger aperture increases the light-gathering capability of the binocular, but does not determine FOV or actual magnification, although aperture does influence USEFUL magnification.

In general, the greater the magnification, the smaller the FOV, but in your examples, the magnification is the same for both, 20x. The difference in FOV is a result of the lens elements in the eyepieces of the two different binoculars.

It's the same for telescope EPs. You can buy, for example, an 11mm Plossl with an apparent FOV of around 50 degrees, or an 11mm ES wide angle EP with an apparent FOV of 82 degrees. The magnification is the same in any given scope, but the FOV is much greater in the second one with any given scope due to the internal lens element design.