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Message: <blockquote data-quote="henry link" data-source="post: 3187882" data-attributes="member: 6806">The ISO method for calculating  AFOV is only correct for a condition of zero rectilinear distortion. Pincushion distortion causes the AFOV to increase above the standard. Barrel distortion causes the AFOV to decrease below the standard. I notice that Dan reported seeing barrel distortion causing a "fisheye" effect with this binocular on another thread. That would certainly result in an apparent field narrower than the ISO calculation, but genuine barrel distortion is rare in binoculars. A more likely condition would be one with almost zero rectilinear distortion. That causes the infamous 'rolling ball", which resembles a "fisheye" effect and might be what he is seeing. If that's the case 59º is about right for a 10x binocular with a 6.5º field. Of course it really hasn't been established that the magnification is exactly 10x or that the FOV is exactly 6.5º.Henry</blockquote>