In a theatre, on a computer screen, in a handheld mobile device, or in an AR headset, the angle from one edge of the view area to the opposite is commonly referred to as the angle of view or field of view (FOV). For example, a typical movie theatre screen is about 54 degrees; an IMAX theatre screen is 70 degrees. The human eye has about 160 degrees horizontal (monocular) or 200 degrees combined binocular FOV. The HTC Vive VR headset has about 100 degrees. Note that sometimes FOV is reported as separate horizontal and vertical; other times, it's a (better-sounding) diagonal measure.

Although not commonly discussed this way, when you hold a mobile device in front of you, it does have a field of view that is measured by the size of the screen and how far away you're holding it. So, an arm's length, about 18 inches away, is just 10 degrees or so. This is why you often see people preferring a large screen tablet for mobile AR rather than a phone.

When it comes to wearables, the expectations are greater. The Microsoft HoloLens FOV is only about 35 degrees, equivalent to holding your smartphone about 6 to 8 inches in front of your face or using a 15-inch computer monitor on your desk. Fortunately, despite the limitation, users report that you get used to it and learn to move your head instead of your eyes to discover and follow objects of interest in AR. Metavision Meta 2 does better; it's FOV is 90 degrees (diagonal).

The following image illustrates the effect of FOV when you wear a HoloLens device (image by Adam Dachis/NextReality):