Originally Posted by neuroanatomist
While it's true that pixel size is generally less important than sensor size when it comes to affecting DoF, I wouldn't go as far to say that it has no effect. Here are some other factors that affect DoF:
- Aliasing
- Processing (e.g. demosiac, sharpening)
- Display size
- Viewing distance
- Display resolution
- Viewer acuity
- Viewing environment
All of those factors and more can affect what can be discernable by the viewer as acceptably sharp.
For example, let's say I take a self-portrait and find that it looks perfectly sharp on the rear LCD of my camera such that about 3 feet (object space) looks in perfect focus. It could not be any sharper. Then, I get home and put it on the computer and decide to use it for my 30-pixel TDP avatar image. But at this reduced size, what used to be a blurry background is now much sharper, so the DOF is now more like 10 feet. The maximum sharpness for that display is achieved over a wider distance in object space.
Then I decide to make a 4x6 print. Now that I can see a lot more resolution, it becomes clear that some of the image is far sharper than other parts. Now it is possible for some of the image to be sharper, but it isn't. The acceptably sharp standard has changed again, but in the other direction. Now it's clear that the image is slightly front-focused, and the DOF only looks like 6 inches.
Next I make a 30x20 blow-up. Now it's painfully obvious how badly out of focus the image is. Add a more detailed demosaic and additional sharpening and it becomes even more clear just how thin the very sharpest part of the image is.
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] Perhaps I should have stated that as, "pixel size has no effect on the DoF value reported by standard calculator tools such as DoFMaster." Certainly, since true DoF is defined by that which is perceived as acceptably sharp, as opposed to that which is not, many other factors come into play. Here's one more for your list: