Just checking my sanity: I find all measures of field of view quantification nearly useless except the "apparent field of view" one (AFOV). Am I the only one? Just curious.
The AFOV tells me immediately what I'm going to see. Other measures of the visual field seem quite opaque: both the true field of view (TFOV) and the linear measure tells me nothing without factoring the magnification in, so I need to develop one intuition per magnification!
Whenever I see a TFOV, I multiply it by the magnification to get the AFOV, and whenever I see a linear measure I reach for my HP calculator with the relevant equation for the AFOV programmed in.
Am I missing something? I guess the linear measure might be useful for someone watching the same large object of known dimensions every day. But that doesn't seem to describe birding?
The best indicator to field of view imo is the actual angle of view, which seems to be 7-8 degrees for most good birding glasses. There have been much wider angle offerings (some with 11-12 degree fields), but these offered too little eye relief to be broadly usable. A modern wide angle glass with longer eye relief would be a very welcome innovation.
I've not been able to relate to the other measures, particularly apparent field of view. But then I've not been able to make much sense of the twilight factor either, yet it too seems to be a highly regarded measure of something.
It's good that there is always something to learn.
I agree etudiant. The tfov is most useful figure for me. In degrees is best but I now know roughly what measurement in m/1000m relates to what degree measurement so either is useful to me.
The tfov tells you how wide a view you are seeing, whether that's at 7x, 8x, 10x, etc is neither here nor there. If the tfov is 8*, it's 8* at 7x and it's 8* at 8x.