Review Mini review of Tamron 90mm (A7R5 | MFO-1)

[BoltSnap]

I don't get your second question, but the MTF of the lenses drops significantly beyond f/16. There are several physical / engineering factors for this.

I am fasting, so please excuse my slow mental state

In this context, does one have to set the lens's aperture at exactly f/16? They can't set it to f/22 or f/11 (or anything else).

 

[DragonUW]

Ah, OK - BTW, have a rewarding fast.

With high-resolution sensors, it will always be a compromise. A lower aperture, such as f/22, will give you a higher DOF, but the overall resolution (read image quality) will suffer. Apertures between f/11 and f/16 are a sweet spot for modern macro, in my opinion.

 

[Barmaglot]

In this context, does one have to set the lens's aperture at exactly f/16? They can't set it to f/22 or f/11 (or anything else).

You can set it to anything in the range from f/2.8 to f/16. It's not a fixed-aperture lens, but it can't go any narrower than f/16, which is a bit of a weakness. Sony 90mm is already limited to f/22, which is wider than most other macro lenses' f/32. While it is true that very small apertures cause overall image degradation due to diffraction, in many cases it is a worthwhile tradeoff for the increased depth of field. On land, with static subjects and a tripod, it is often possible to focus stack so as to get the required depth of field without diffraction-inducing apertures, but underwater it is a great deal more difficult to pull off.

 

[hedonist222]

While it is true that very small apertures cause overall image degradation due to diffraction, in many cases it is a worthwhile tradeoff for the increased depth of field. On land, with static subjects and a tripod, it is often possible to focus stack so as to get the required depth of field without diffraction-inducing apertures, but underwater it is a great deal more difficult to pull off.

Agree with this.
I took it a step further to decide what works best for me when I had my Canon 5D mkII and Canon 100 f/2 L lens.
I found that I absolutely needed between f18 and f/26.
I then did tests on the same subject from f/18 to f/28 or similar.

I found that remarkable degradation took place beyond f/22 on the Canon lens. No issue because I was okay with f/22.