Binocular manufacturers often load up their ads with a ton of high tech data to impress someone looking to buy binoculars. Hey, if it sounds "scientific" it must be good, right? Actually, no, not unless you know the basics on optics. All that high tech jargon can just as easily confuse a customer that wants to buy a birding binocular, for instance and needs to compare one binocular model to the next.
Field of view, for instance, is one spec that is sometimes posted in a variety of ways. When birdwatching, for instance on birds at short range, a wide field of view can be a real advantage. So, how do you translate and compare field of view in a binocular when it can be listed as true field of view, apparent field of view or, most commonly, as feet at 1000 yards, though sometimes we go metric and advertise meters at 100 meters. Help!
True field of view (also known as angular field of view) is the measurement in degrees of how much sky you can actually see with the binocular expressed in degrees. You can easily convert this to the more familiar feet at a thousand yards by multiplying the degrees by 52.5 to get your feet at 1000 yards.
Field of view expressed as meters at a thousand meters is also quite simple. Just multiply the meters by 3 to get your approximate feet at a thousand yards. It will be plenty close enough for comparison sake.
Apparent field of view is more commonly used with telescope eyepieces, but now and then. you will see it used to specify field of view in binoculars. Just divide the apparent field of view by the magnification and you get the true (apparent field), then just multiply by 52.5 and you are back to feet at a thousand yards.
Okay, for your homework ....