John Russell
Well-known member
Browsing through the new Nikon Sport Optics catalogue, I notice that Nikon have now adopted the ISO 14132-1:2002 standard for apparent field of view.
The 8x30 E II for instance has a FOV of 154m @ 1000m, which corresponds to 8,8°. We would up to now have defined the AFOV as 8x8,8°, i.e. 70,4° but the new ISO standard is that the AFOV is equivalent to viewing the 154m from a distance of 1000/8, i.e. 125m.
The angle corresponding to a tangent of 77/125 is 31,6° so the AFOV is now twice this, 63,2°, which is the value now quoted in the Nikon catalogue.
While Nikon's honesty is to be commended, I question whether this really makes sense.
AFOV is an attempt to quantify a subjective impression, much like wind chill factor. We know that values over 60° wil be experienced as wide angle and those under 45° as tunnel vision.
There also seems to be a chicken and egg element in that the magnification is used to define a value expressed in tenths of a degree.
How though is magnification measured? I have been unable to find an ISO definition for it as the international standards are not freely available. There are dozens of them appertaining to optics and each costs about 50 Swiss francs!!
Magnification is probably subject to minor design tolerances and also to variations across the field (distortion) so this new ISO AFOV standard seems somewhat absurd and is going to cause confusion if manufacturers use different bases for their calculations.
John
The 8x30 E II for instance has a FOV of 154m @ 1000m, which corresponds to 8,8°. We would up to now have defined the AFOV as 8x8,8°, i.e. 70,4° but the new ISO standard is that the AFOV is equivalent to viewing the 154m from a distance of 1000/8, i.e. 125m.
The angle corresponding to a tangent of 77/125 is 31,6° so the AFOV is now twice this, 63,2°, which is the value now quoted in the Nikon catalogue.
While Nikon's honesty is to be commended, I question whether this really makes sense.
AFOV is an attempt to quantify a subjective impression, much like wind chill factor. We know that values over 60° wil be experienced as wide angle and those under 45° as tunnel vision.
There also seems to be a chicken and egg element in that the magnification is used to define a value expressed in tenths of a degree.
How though is magnification measured? I have been unable to find an ISO definition for it as the international standards are not freely available. There are dozens of them appertaining to optics and each costs about 50 Swiss francs!!
Magnification is probably subject to minor design tolerances and also to variations across the field (distortion) so this new ISO AFOV standard seems somewhat absurd and is going to cause confusion if manufacturers use different bases for their calculations.
John