Is it possible to find the distance to which the camera is auto focussing ?
Camera auto focuses itself to view a particular plane in the real world in front of it. Is it possible to estimate the distance of this focusing plane?
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If your lens has a distance scale it will indicate the approximate distance to the point of focus as measured from the film/sensor plane. In the image below, the point of focus is 1.5 meters (5') in front of the film/sensor plane. As the point of focus approaches infinity, the distance measurement becomes less precise. In general, the longer the focal length of the lens, the further the distance of the last index mark before infinity.
Older manual focus lenses often had much more detailed distance scales than modern AF lenses. The f/numbers to each side of the center line indicate what distances would be within the depth of field (DoF) based on the assumption of a 35mm film sized sensor and an 8X10 display size viewed at 25 cm (10") by a person with 20/20 vision. Push/pull zoom lenses often included the DoF scales etched onto the barrel of the lens.