7/31/2023 0 Comments Diagonal fov of zed cameraThis is the marked focal length that applies when focused at infinity. In this equation, we can see that if the subject at s1 is at infinity, then 1/s1 is zero, so then s2 = f. If OK with a little geometry and algebra, you can see the derivation of this classic Thin Lens Equation at the Khan Academy. The distance from the front nodal point to the object in the subject plane (s1), and the distance from the rear nodal point to the image plane (s2) (when focused) are related by this Thin Lens equation (Wikipedia), which the diagram and formulas below simplify. Actual focal length could be determined by the Magnification (Wikipedia) and distance. A fisheye is rather unconcerned about this distortion, and can show a wider view, poorly purists might say, but very wide, and very possibly interesting.įocal Length varies with zoom, and the Exif data with the image should report focal length (in coarse zoom steps, as best it can). A regular lens is rectilinear, meaning it shows straight lines as straight lines, not curved. We are only seeking a ballpark FOV number anyway, we adjust small differences with our subject framing or cropping, but vague guesses about your distance and sensor size or focal length don't help FOV accuracy.Īnd a fisheye lens is a different animal, wider view than this formula predicts. But this calculation does not include macro distances. But generally speaking, focal length becomes a little longer at very close distances (2x longer at 1:1), so field of view could be a little smaller, but should be insignificant as long as magnification is greater than 0.1x, which in regular lenses is normally near their Minimum focus distance. But internal focusing lenses can do internal tricks with focal length (some zooms and macro lenses can be shorter when up close, instead of longer). Lens specs normally indicate this internal extension at closest focus distance. Focal length normally increases when lens is extended forward to focus closer. Furthermore, the Marked focal length is only applicable to focus at infinity. The actual can be a few percent different. The Marked focal length of any lens is a rounded nominal number, like 50 or 60 mm. But errors about that point is only a few mm, and will be insignificant if the field distance is at least two meters (six feet) distance. Otherwise, the distance should measure to around the center of a normal lens length. If a wide angle lens, measure to the rear of the lens. If a telephoto lens, measure to the front element. Distance measurement for this calculation is to some unknown point within the lens body. And of course just guessing about the field distance may not be at all accurate.The image EXIF data may show focal length (but it is rounded in some degree). Zoom lens focal length is different at each and every zoom position.
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