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For the night sky would people prefer the 16x or 20x? Specifically how does the edge correction hold up in the fov of 3.4degree vs 4.2degrees? How significant is the brightness difference in these IS models? And how is the CA and ghosting on bright objects like the moon?
Looks like Fuji have fallen in the same stupid PR trap as Nikon: they started listing the "true" AFOV (which nobody cares about except a technician at an optical bench) instead of the "approximate" AFOV (which everyone uses and understands as it's simply the product of the FOV and the magnification). So, for example, the 20x40 has a 68-degrees AFOV, and nobody cares that on an optical bench it would be 61.4 degrees.
Looks like Fuji have fallen in the same stupid PR trap as Nikon: they started listing the "true" AFOV (which nobody cares about except a technician at an optical bench) instead of the "approximate" AFOV (which everyone uses and understands as it's simply the product of the FOV and the magnification). So, for example, the 20x40 has a 68-degrees AFOV, and nobody cares that on an optical bench it would be 61.4 degrees.
Fujinon does not measure the "true" AFOV at an optical bench. They use the ISO formula, which is no more accurate than the simple formula you prefer. Neither one takes the binocular's distortion profile into account.
Swarovski and Zeiss do measure the "true" AFOV, which almost always falls between the ISO and simple methods. It will be closer to the ISO figure if pincushion distortion is low and angular magnification distortion is high, closer to the simple figure if AMD is low and pincushion distortion is high.