Optimum aperture for 120mm H series lens

[e_tunbridge]

I know that this is discussed often on the forum, but can't find the relevant links.
Has anyone done depth of field tests on any of the H-Series lenses on a Hasselblad or Phase backs.
Often we talk of the optimum aperture of the 120mm to be f19, after which defraction starts to interfere with image quailty and we do not gain any further depth of field. Is this true or heresay? And does anyone one have any image tests to prove it?

Many Thanks in advance

Em
x

 

[polypal]

In general macro lenses offer excellent quality at full aperture.

I would only stop down the lens to increase DOF.
F19 seems way over the limit where refraction starts to have a negative effect on image quality.