Depth of Field Calculator

The zone in front of and behind the focus point that still looks sharp. It is not a hard boundary — blur increases continuously either side of the focus plane, and depth of field is where that blur is small enough to read as sharp at normal viewing size.

Only roughly, and only at moderate distances. Close up the split approaches half and half; near the hyperfocal distance almost all of the depth falls behind the subject. Treat it as a rule of thumb, not a formula.

Yes. A smaller sensor is enlarged more to reach the same print size, so it tolerates less blur — the circle of confusion shrinks with the sensor. At the same focal length, aperture and distance, a Micro Four Thirds sensor gives about half the depth a full-frame one does.

No. Past roughly f/11 on a small sensor, diffraction softens the whole frame faster than the extra depth of field gains you. The sharpest overall result is usually a stop or two wider than the minimum aperture.

Almost always the circle of confusion. This one derives it from the sensor diagonal divided by 1500; many others hard-code 0.03 mm, which is a full-frame value and wrong on anything smaller.