Diffraction blur with the R5 and four prime lenses

Thanks,

In looking at your images, I see a lot of correlation with what I have found with the RF-L zoom lenses (reported here https://www.dpreview.com/forums/post/66394314). Namely, the sharpness will peak near f2.8 or f4 and then remain pretty flat through f5.6. It might dip almost imperceptible at f8, drop off very slightly at f11 and then drop significantly at f16.

I took your two sets of images for the 50f1.2 and 85f1.2 (putting the corners and centers adjacent to each other) and then ran a "find edges" to help identify the sharpest part of the background texture (based on a trick taught by Roger Cicala at Lensrental: https://www.lensrentals.com/blog/2016/09/fun-with-field-of-focus-part-1/).

The find edges operation causes textures to be darker where they are sharper. I marked below where it looked to me like the peak sharpness. Note it is very flat from f2 through f5.6 for both lenses. As expected, the mid-corners peaked at a high f-number. Similarly, for worse lenses, the peak sharpness tends to be at higher f-numbers, but then sharpness starts falling off slightly at f11 and then more severely by f16.

A bit of a surprise for me in the whole process of checking many lenses I have tested is the consistency with which the diffraction is a function of f-number (a ratio) and not the absolute dimension of the aperture regardless of the focal length or lens quality. I consider f11 to be kind of the sweat spot for improving DoF without significantly hurting the center resolution. This would also suggest that the RF600f11 and RF800f11 are not significantly hurt by diffraction due to the higher f-number.

theninth wrote:

Karl_Guttag wrote:

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.

I have also done a series of the corners, see below. Images are not taken from the extreme corners but roughly at 2/3 of the line between the center and the corner. By and large it seems to me that the aperture of highest sharpness remains the same as in the center, the RF glass is already very sharp at F2.8, while the older EF glass peaks at F5.6 to F8.0. The biggest difference is seen wide open, where the quality of the EF 35 F1.4L (I) is noticeable worse than in its center and the EF 135 F2.0L also shows some falloff, albeit to a lesser extend. Compared to that, the newer RF glass already wide open delivers very good results in the corners.

Here are the images:

And here the overview of the complete test scene: