This is one of the easier calculations in optics. Apparent FOV is simply the True Field of View times magnification(or power).
A 20X binocular with 3.5 deg FOV will have APFOV of 20X3.5= 70 deg.
Most binoculars list TFOV or how many feet/1000 yards. For example my Eagle Optics 8X32 has FOV of 393 ft at 1000 yds. One deg FOV is ~52.4 ft/1000 yards. My EO has TFOV of ~7.5 deg or 60 deg APFOV.
Mike's Vixen 16X80 is listed as having FOV of 4.3 deg. APFOV is 68.8 deg. Fairly wide for a EP.
I usually prefer my binos to have at least 60 deg APFOV. EdZ measured the Burgess 20X80 LW to have 3.8 deg TFOV sometime ago. That's very wide 76 deg APFOV. Do expect edge distortion with such wide angle binos. My Celectron Nova 7X50 is listed as having 10 Deg TFOV/70 deg APFOV. It's almost like viewing thru a fisheye lens at night. Stars in the outter 20% of the Field are totally distored.
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Re: Update: Very Short Test on Vixen 16x80 Binocul
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