Because the image sensors in many digital cameras is smaller than the 24 mm×36 mm image area of full-frame 35-mm cameras, a lens of a given focal length will give a narrower field of view on such cameras.
The size of a sensor is often expressed as optical format in inches.
Considering a picture with the same subject distance and angle of view for two different formats: .
Using the same absolute aperture diameter for both formats with the “same picture” criterion (equal angle of view, magnified to same final size) yields the same depth of field.
This test is implemented in the Windows Hardware Certification Kit (Windows HCK).