Diffraction can be a a problem, but nevertheless, sometimes stopping down more is the best solution. Depth of Field can be worse than diffraction. More images. Again, these are FX D800 36 megapixels, and DX D300 12 megapixels. We are not comparing FX/DX, we are looking at f/22 in each.
Next is the main scene, with 50 mm lens and FX, and in order to see details bigger, both FX and DX below are selecting the crop to be the same 20% of the frame size (D800 7360 wide becomes 1467 crop, D300 4288 wide becomes 855 pixels crop). Then both size crops are resampled to 600 pixels width, which for FX is about 40% size (of this small crop), and DX is about 70% size, The DX enlargement is greater, in order to appear same size as FX. Saying again, as in real life, the DX frame is enlarged half again more than FX.
The focus is on this center fence pole at about 20 feet, so we are not using the depth of field in front of it. This gives up overall depth of field, but it keeps sharp focus on the near subject. The first table is pushing 100 feet. The 24 and 14 mm lenses also moved up to only five feet from the near fence pole.
Point is, f/22 ought not be a routine norm, but I sure don't see any problem with using it when it helps needed depth of field. And f/32 on longer lenses that provide it.
For the short lenses, f/22 is closer to focal length / 1 instead of 4, which violates the rule of thumb given on previous page. It shows, especially if image object size is smaller.
With 50 mm lens, maybe the f/22 difference at focal length / 2 is debatable, at least for DX. Again, these are very large enlargements.
With longer lenses, even in these very large enlargements, any difference in sharpness at f/22 is pretty difficult to see (other than depth of field).
It is not about pixel size. And you should try this. Otherwise, when needed, you're missing out on a good thing.
