Field of View Calculator

In short Angle of view is pure geometry: two times the arctangent of the sensor dimension divided by twice the focal length. Nothing about the lens design enters into it, which is why a 50 mm lens from any maker frames identically on the same camera. A 50 mm on full frame covers 39.6 degrees horizontally and 46.8 diagonally, and the diagonal figure is the one lens makers quote. Because there are three sensor dimensions there are three angles, and quoting the wrong one is where most disagreements between sources come from. The formula also explains coverage: at a distance much greater than the focal length, the width you frame is simply the distance times the sensor width divided by the focal length. That is how you work out how far back to stand — a 1.8 metre person fills the frame vertically on full frame with a 50 mm lens from about 3.75 metres. The point worth internalising is that perspective is not a property of the lens. Two lenses used from the same spot record exactly the same perspective; the longer one just crops into it. What flattens a face in a portrait is standing further back, and the long lens is only how you frame the shot from there. Change lens and distance together and the perspective changes; change lens alone and only the crop does.