Originally Posted by retinax
No-one disputes that one can stop down. However Ming Thein talks about hand held photography, so the price to pay for stopping down beyond a certain point is higher ISO, as he points out. Which may still be better, or not.
For tripod photography your point stands. Even more, I doubt that diffraction actually doubles per f/stop down that is needed to get the same dof for FF compared to APS-C, because the length of the edge of the diaphragm (which is responsible for diffraction) doesn't change in a linear way with the size of the aperture. Or does it? Maybe because we need to consider the different aperture size needed for the different focal length to get the same fov. Ok I'm in over my head.
This was a seperate rant unrelated to Ming’s article...
It doesn’t exactly double, but it’s close enough (there’s a small angle approximation in there). Regarding the different linear changes when focal length changes, the f in f-stop is normalising for focal length. We need to un normalise it for depth of field. So, stopping down to f/8 on a full frame lens is the same linear aperture size as stopping down to f/4 on m43 for the same angle of view. Depth of field is related to the actual aperture size.