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Message: <blockquote data-quote="henry link" data-source="post: 2756142" data-attributes="member: 6806">Rather than using the ISO standard or the simple real field x magnification calculation, Swarovski appears to me to actually measure the angle subtended by the apparent field, which would include the effects of distortion. Pincushion causes the apparent field to be larger than expected from the real field while barrel and angular magnification distortion cause it to be smaller. The Swarovisions have a compound distortion pattern; pincushion in the center half of the field which then reverses to angular magnification distortion near the edge. I'm sure the "real" apparent field could be calculated for such a distortion scheme, but it's also easy to simply measure it. If you have a tripod head with a degree scale for panning motion you can sight the eyepiece field stop through the front of a binocular mounted on the head. Position a small object at one side of the field stop, then rotate the head until the object moves to the other side. Read the change in degrees on the panning scale. That's the true angle subtended by the apparent field.</blockquote>