Last summer I tried to approach the AFOV concept in a new way.
http://www.birdforum.net/showthread...964#post1892964
The result might be named "PFOV" for Perceived Field Of View. It has also been called transparency or walk-in.
To me, it's very obvious that AFOV does not tell everything about how the view through binoculars feel. Some of my ideas in that post are not correct, and I'm still trying to find out all the factors that promote the walk-in experience.
At present, I believe those are:
1) Sleek design of the housing, eyecups and barrels
2) Large ocular lenses + thin rim around them
3) Great eye relief
4) Eyecups collapsed
5) To certain extent, AFOV
In the next post, I've made a simple illustration.
The illustration is schematic. For example, the pair of eyes and the two barrels are made one.
The green, central part is what you see, the image and the apparent FOV.
The light green areas are what the human visual field perceives.
The grey area is what's beyond the human visual field (slightly beyond 180 degrees).
Finally, the red area is what is obscured by the field stop, the rims, the housing of the bnoculars and the hands. One might call this "negative PFOV".
If the hands are further away from the eyes they will obscure less of the human FOV.
# I is a non-wide angle binocular with the eyecup extended.
# II is the same sample with the eyecups collapsed.
# III is a wide angle binocular with the eyecup extended.
# IV is an equally wide angle bin with sleek eyecup design and eyecups collapsed.
The image portion of # III is greater than # I and the obscured part of the visual field is smaller.
Same thing happen between #II and # IV, but the sleek eyecups of # IV adds a few extra degrees of PFOV. If the eye relief allows holding the bins further away, the open area will increase, and the hands will get more out of the way.
As follows, a great AFOV is advantageous for the walk-in experience because it expands from the center towards the obscuration.
But if the outer edge of the obscuration/"negative PFOV" is further out, it will decrease the PFOV.
So, as little obscuration as possible is desired. IMHO.