Questions about how much of the scene a camera can see, and what can affect how much is seen.

The field of view (FOV) is the angle between the edges of a frame in one dimension (horizontal, vertical, or diagonal). Usually, we are talking about diagonal FOV, because in rectangular frames, the diagonal is larger than both the width and the height (the Pythagorean theorem states that d = √( h² + w² ))

FOV [°] = 2 * arctan ( d [mm] / (2 * f [mm]) )

FOV is our field of view in degrees, d is one of the dimensions of the sensor (height/width/diagonal) in millimeters and f is the focal length in millimeters.

Because the is a fixed value that is determined by the lens's properties, and because the influences the FOV (see ), it is common to talk about "focal length equivalent to 35mm".

e [mm] = f [mm] * c

e is the equivalent focal length in millimeters, f is the focal length in millimeters, and c is the crop factor (c = A35mm[mm²] / ACropped sensor[mm²], where A is the sensor area in square millimeters) )

While the focal length does not change, because the smaller sensor sees less of the image circle, it has a smaller FOV, for which you would have to use a longer focal length lens on a 35mm (full frame) camera.

Further reading: