Depth of Field Calculator

In short Depth of field is the range of distances that look acceptably sharp, and it comes from four things: focal length, aperture, focus distance and how much blur you are willing to call sharp. That last one is the circle of confusion, and it is a convention rather than a measurement — the sensor diagonal divided by 1500, which is about 0.029 mm on full frame and works out to roughly what a person can resolve in a normal-sized print at a normal viewing distance. Every depth-of-field figure anywhere rests on it, which is why the same photograph has less depth of field the bigger you print it. A 50 mm lens at f/8 on full frame focused at 3 metres is sharp from 2.36 to 4.12 metres. Stop down to f/16 and it runs from 1.94 metres to 6.59. The rule that a third of the depth is in front of the subject and two thirds behind is only true near the hyperfocal distance and nowhere else: close up the split approaches half and half, and far away almost everything is behind. This tool prints the actual split rather than repeating the rule. Three things move depth of field far more than people expect. Focal length matters as its square, so a 100 mm lens has a quarter the depth of a 50 mm at the same aperture and distance. Distance matters as its square too. And sensor size enters twice — a smaller sensor has a smaller circle of confusion, but you also stand closer or use a shorter lens to get the same framing, and the second effect wins, which is why a phone struggles to blur a background and a medium-format camera cannot avoid it.