if u are talking about about 30d and 1d mk3. i don't really think there will be any difference. but if u are comparing a digital slr camera to a digital range finder camera. then i think u are absolutely correct. they have another size of matrix? i m not quite sure what u are referring to. are u talking about the size of color sensors? in fact, the size of the sensor doesn't has any effect on altering the focal length or depth of field. that is a common misunderstanding of cropping factor of most people today. it won't be difficult to understand if u have experience of using a photo enlarger with a fixed magnification on two different size of papers. u should know what i mean now.
DOF on a smaller sensor will decrease only if the picture is enlarged by the crop factor to match the same picture size of a full sensor. But DOF of a 1.6 crop size sensor, using the same focal length and aperture and taken at 1.6 times the distance of that of a full sensor, will increase over that of the full sensor.
All 3 cameras, Canon 30d, Canon 1d mk3, and Nikon 700 have different size sensors. If the same focal length lens and the same aperture are used and the picture taking distance is the same, all 3 cameras will have different DOF if prints from the 3 cameras are enlarged to the same size. The bigger the sensor the shallower the DOF.
