Quote Originally Posted by iND
Please try to explain why larger sensors will have a greater depth of field at the same lens/aperture/distance

Because of reproduction magnification (AKA "enlargement ratio").


For example, let's say 135mm on full frame shows the entire head of a portrait and the eyes and nose are both in focus. Now switch the camera to 1.6X crop without changing focal length, f-number, or subject distance. You can no longer see the entire head -- just from the eyebrows to the chin. And now the eyes and nose are 1.6X larger. With that larger size, it's apparent that the front of the nose is actually slightly outside the depth of field.


Now, what if you had cropped the full frame image to match the same angle of view (eyebrows to chin) as the 1.6X image? Then the DOF would go back to being the same -- but only if the limiting resolution was the same. For example, the 20D and 5D2 have the same 8 MP if they are cropped to the same angle of view -- so in that case they would have the same DOF. But if you compared the 5D2 cropped to the 7D, it is possible to see thinner DOF on the 7D due to higher limiting resolution.


Hope that helps.