I recall quality from the Canon 100 f/2.8L began degrading at f/24.

 

I have not yet tested the Sony 90mm yet.

 

Has anyone established this yet? 

Hi Hedonist,

 

The loss of resolution, due to diffraction, is pretty similar between these two lenses (stopped down the resolution of different sensors is by far not limiting):

 

https://www.lenstip.com/214.4-Lens_review-Canon_EF_100_mm_f_2.8_L_Macro_IS_USM_Image_resolution.html

https://www.lenstip.com/561.4-Lens_review-Sony_FE_90_mm_f_2.8_Macro_G_OSS_Image_resolution.html

 

The smallest aperture possible with Sony 90mm is f/22 (probably because of the problem of loss in resolution).

It is, of course, a matter of personal taste, and much more of the required DOF, how much one stops down such a lens, but (theoretically) best results are obtained at f/4...

 

Wolfgang

Edited September 22, 20241 yr by Architeuthis

All macro lenses lose resolution as they stop down due to diffraction. Here is the MTF testing on lensTips:

 

https://www.lenstip.com/214.4-Lens_review-Canon_EF_100_mm_f_2.8_L_Macro_IS_USM_Image_resolution.html

 

and the 90mm macro:

 

https://www.lenstip.com/561.4-Lens_review-Sony_FE_90_mm_f_2.8_Macro_G_OSS_Image_resolution.html

 

The numbers are not directly comparable as they are tested on different sensor resolutions but you can see a drastic drop in quality at f16-22, so I expect you will see degradation at similar apertures on both lenses.  The plots basically measure resolution and you can see it reduces after f11 or so.  Optical limits also has a plot which is a little more complete for the 100mm f2.8 only, the dramatic drop beyond f16 is more obvious:

 

https://opticallimits.com/canon/canon-rf-100mm-f-2-8-l-usm-is-macro/

 

 

7 minutes ago, Architeuthis said:

Hi Hedonist,

 

The loss of resolution, due to diffraction, is pretty similar between these two lenses (stopped down the resolution of different sensors is by far not limiting):

 

https://www.lenstip.com/214.4-Lens_review-Canon_EF_100_mm_f_2.8_L_Macro_IS_USM_Image_resolution.html

https://www.lenstip.com/561.4-Lens_review-Sony_FE_90_mm_f_2.8_Macro_G_OSS_Image_resolution.html

 

The smallest aperture possible with Sony 90mm is f/22 (probably because of the problem of loss in resolution).

It is, of course, a matter of personal taste, and much more of the required DOF, how much one stops down such a lens...

 

Wolfgang

 

Thank you for this helpful input, Wolfgang. 

 

You are most correct in that, aside from degradation, there are other more commanding variables.  Such as DoF as above. 

 

I actually did test the lens from f22 to f16 but I am opting not to rely on it (test results) because my subject was not stationary. It was fast moving a nudibranchi and therefore my area of focus shifted between shots. 

I will repeat this with a polyp or similar soon. 

Edited September 22, 20241 yr by hedonist222