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Message: <blockquote data-quote="Surveyor" data-source="post: 1533001" data-attributes="member: 50720">Henry, I have been meaning to do further experimenting with this, but since AFOV is not high on my list of priorities, I keep putting it off. I also do not have any published specs on these values. I suspect that the method described actually measures the true acceptance angle, but I suspect that it is being modified by magnification differences. I think I may have found a way of correcting that but have not got around to trying it yet. The last time I mentioned the method no one showed any interest, so I have just been doing as a curiosity instead of a routine parameter. Refer to a simple test at <a href="http://www.birdforum.net/showpost.php?p=1337144&postcount=7" target="_blank">http://www.birdforum.net/showpost.php?p=1337144&postcount=7</a> At the time of this post I did not know the specification of the Zeiss. This little Zeiss, I found out later, has a spec of 351’ @ 1000 yds. which would give the results of acceptance angle=53.6 degrees and ISO angle of 50.2 degrees. Using the protractor posted, I measured the right barrel just now at 52.5* but without the benefit of a good target.  When time permits, probably next weekend, I will bring my 1 arc second “protractor” home and set up several binos. I think by measuring both the acceptance angle and then swapping ends and measuring the true field of view that I can get a better definition. Note that above I say I have measured the Promaster at 59* and I think it has a spec of 60*. The ISO prediction for that bino is 55.34*. I also measured an 8x36 Monarch. I only measured the TFOV on the right side at 6.97 degrees and the eyepiece acceptance angles as 54.35 left and 54.33 on the right side (probably should be 56 degrees). These angles should be considered very approximate. The prediction of my AFOV program says 56* acceptance angle and ISO 52.2*. The above figures suggest a magnification of 7.8x for the right tube and I may have measured the power of these before. I will hunt for that. It was very hard to get good measurements because the apparent magnification is about 0.125 and 60 degrees wide and when viewing, a shadow or dark transparent band several degrees wide would manifest itself along the edge making the edge hard to determine and appearing to shift a little with the shadows appearance.  On another note I have found that measuring the field stops in the exit pupil with a good optical sighting magnetic compass, Suunto KB 14 in this case, that I get very close to the ISO value. I will get back after some more testing. BestRon</blockquote>

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