OMG...tell me thiis guy is wrong about micro four thirds

Bob Meyer wrote:

That's not really quite right, either. Sensor size has nothing to do with DOF. Aperture diameter (not f-stop) does. A 50mm f/2 lens on an m43 camera will provide exactly the same DOF as a 50mm f/2 lens on a FF camera (or an APS-C camera). Obviously the field of view is different, but if you crop the FF shot to match the crop factor of the m43 shot, they'll look identical.

The reason we tend to think smaller sensors cause greater DOF is because we use shorter focal length lenses to match the FOV of what we're used to on larger sensors. And the aperture of a 25mm lens at f/2 is half the diameter of the 50mm f/2. It's that smaller aperture that is responsible for the greater DOF.

Focal length doesn't affect DOF either, except as it impacts the diameter of the aperture. It's the change in subject distance (you usually use telephotos from greater distances, and wide-angles closer up) that affects DOF. If you shoot with a 200mm lens from 20 feet, or use a 50mm lens and crop the image to match that of the 200, and use apertures of the same diameter (e.g. f/2 on the 50mm lens, f/4 on the 200), you'll have identical DOF.

So the two things that affect DOF when shooting are aperture diameter (not the same as f-stop) and distance.

At the other end of the image chain, enlargement of the final image and viewing distance also affect the DOF perceived by the viewer, but that's a longer topic.

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