For moderate subject distances, the

**total depth of field** (near to far) is proportional to fnR**2 where

f=focal length

n=aperture

R=reduction (= 1/magnification)

For a subject of a given size (say a head and shoulders portrait) the reduction R is proportional to 1/L where

L = sensor dimension

Since we are only interested in a ratio, we can take any consistent sensor dimension in the comparison – diagonal, horizontal side, or vertical side. Choose 11 mm diagonal for 2/3" sensor, 22 mm diagonal for 4/3" sensor.

Comparing the total depth between the X10 and a M4/3 camera shows

**it is a wash**, using f2.8 for the X10, and f5.6 for a kit lens on an Olympus Pen E-P2, say, using the ratio of crop factors for the ration of focal lengths.

Terry's calculations essentially agree with this.