Diffraction blur with the R5 and four prime lenses

thunder storm wrote:

Karl_Guttag wrote:

RogerZoul wrote:

Seems like in the real world, or in real world use, you can get away with F11 using all of those lenses except maybe the 35mm.

Additionally, these were from the center of the image, which benefits the least from stopping down. I would expect that corners would peak at a somewhat higher f-number.

As a practical matter on most lenses, it does seem that there is only a slight fall-off due to diffraction between f8 and f11 but a more dramatic falloff going to f16 and beyond (you hit the knee of the diffraction curve). Certainly, as you stop down from wide open, the diffraction is getting worse, but this is usually offset by the improvements in other ways by stopping down. With top-notch lenses, you can see the image soften slightly in the center within one stop of wide open,

That's new information for me. So diffraction also plays a role before the so called "diffraction limited aperture", not only beyond it?

"Diffraction limit" is basically when you can't resolve two lines due to diffraction. Diffraction is an analog effect and not all or nothing. Whether your images are limited by diffraction depends on many factors, including pixel size. As pixels get smaller (and thus can resolve more lines per mm) diffraction has a more significant effect.

but it is not dramatic as it gets between f11 and f16. With cheap zooms, you may have to go beyond f8 to peak the sharpness.

The "generic" curve below from a Canon white paper shows that "focus aberrations" improve dramatically as the camera stops down while diffraction gradually worsens. If you combine the red and black curves, you get the net.

Then you have to consider that this curve is for one spot on the image; you will find the red curve for the outside part of the image will be much worse than for the center. As you stop down, the outsides will improve as the center will start to soften. So there is a bit of a balancing act as to which aperture would give the best overall sharpest image.

The bottom line is that a top-quality lens in the center with a high-resolution camera will start softening due to diffraction almost immediately.

From: https://teltec.de/out/media/canon-eos-r-white-paper.pdf