Field of View / Depth of View
Think of field of view as “how far across” and depth of view as “how far front to back”.
Field of view is the angle which can be seen across the image circle. With very high quality binoculars, this is the entire width of the image circle. With low quality binoculars, it’s almost irrelevant as the image starts to degrade away from center.
A narrow field of view feels constrained and is not as enjoyable because it cuts off context.
A wide field of view is sheer pleasure, and allows one to see “more of the action”, which might matter at sporting events, glassing a harem of cow elk for that big bull, etc. That’s one reason a 7X binocular can be so appealing.
Field of view is quoted in degrees and/or width at a distance. For example:
Fujinon 7X50: 7.5° = 394' @ 1000 yards / 131m @ 1000m
Leica 8X42 Geovid: 7.0° = 368' @ 1000 yards / 122m @ 1000m
Zeiss Victory 8X32: 8.0° = 420' @ 1000 yards / 139m @ 1000m
Although the Zeiss 8X32 is quote at 8°, its field of view seemed narrow than the Fujinons.
As magnification increases, the field of view narrows. To get the widest field of view you generally need a lower magnification, such as 7X or 8X.
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Usable field of view
As important as field of view is the quality of the view away from the center: with a low quality binocular areas away from center can start to smear, or have color fringing. A high quality binocular yields sharp and clear images over the entire viewing area.
Also, without enough eye relief, you might get some “tunnel vision” effect. There is no substitute for actually looking through a binocular.
Binoculars have a depth of field characteristic just as in photography: how blurred the image looks away from the focused area.
The Fujinon 7X50 binoculars uses porro prisms, and it was amazing to see how much more was in focus using them compared to the Leica or Zeiss roof-prism binoculars.
I had no idea this difference existed: look through the Fujinons and you’ll immediately notice that near-to-far sharpness is much better.
Unfortunately, while porro prisms provide outstanding depth of view, the porro prisms makes the binoculars bulky and somewhat awkward in shape. By comparison, roof prisms allow a compact design, along with a central focus knob— very quick and handy.
The Fujinons (with Porro prisms) require focusing both eyepieces; there is no quick and easy center focus. Still, for any use where the subject moves about within a reasonable zone (eg sports), the Fujinons provide an image which requires no adjustment, whereas the other models I tried required constant adjustment for modest changes in distance. It all depends on what you’ll be viewing.