 Manley S. Minsker |
Field of View for Telephoto Lenses Binoculars give a specification they call field of view such as objects will appear 231 ft at 1000 yd. Is there a way to determine the same thing for telephoto or zoom lenses? What distance will an object appear to be at 1000 yds away for a 300mm lens for instance?
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Michael H. Cothran |
Binoculars have the advantage of "seeing" more like your eyes, since you are looking through TWO lenses at the same time (one on each eye). All lenses are identified by an "angle" of view. For instance, a wide angle lens may have a 75° angle of view, while a certain length telephoto might have an 8° angle of view. Check out an online source such as www.bhphoto.com, and search for a specific lens. B&H gives you all the specs on the lens, including its angle of view. You could also just vist the home site for Nikon, Canon, etc. They will also give you all these specs. By definition, ANY 300mm lens on a 35mm camera will have the same angle of view. All this said, here is an easy thing for you to remember when trying to determine such specs. Consider the 50mm lens to be "normal." A 100mm lens will show you an image 2x, and a 300mm lens will yield an image 6 times as large as the 50mm. In other words, your bird would be 6 times as large with the 300 as with the 50, if you stood in the same place for each. Conversely, if you are standing 10 feet from your subject with your 50mm lens, you could stand 60 feet away with the 300mm, and get the same size image, and conversely again, if you were standing 30 feet away with your 300, it would look the same as if you were 5 feet away with your 50. Hope this helps somewhat. Michael H. Cothran www.mhcphoto.net
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Jon Close |
Given the lens's angle of view (usually given for the diagonal), a little geometry yeilds the equation: Field of View (ft at 1000 yds) = 6000 x sin (Angle of View / 2), or 52.4 ft/degree On a 35mm film camera, a 300mm lens gives a diagonal field of view of 8.25° = 423 ft. at 1000 yds. On a 1.6x digital SLR, the angle of view given by 300mm lens is appoximately 8.25°/1.6 = 5.16° = 270 ft. at 1000 yds.
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Manley S. Minsker |
Thanks to both of you, your responses helped.
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