Try looking at the Doctor Optic website for the LF Tessar's, you will have to use the Internet archives, (my saved copy is in the UK), f22 is Zeiss/Doctor Optics recommended aperture for optimal performance. I originally found the link to the Doctor Optics site via Perez/Thalman a few yeras ago. Other manufacturers (Schneider/Rodenstok) give much of their data on coverage etc at f22, this is f-stop they general chose for measuring movements.
One problem is that lens tests like Chris Perez/Kerry Thalman are very subjective and made from images of test charts and while very useful they are based on small samples of each lens - usually just one, although there are exceptions ie 90mm Angulons etc. Few LF lenses are flat field lenses so shouldn't necessarily give high resolution results of a test chart at all apertures, but you would expect process lenses like G-Claron's or Artar's to possibly perform better under these circumstances.
Another issue not covered by Perez/Thalman or MFT testing is the actual use of a lens in real life situations, particularly when Depth of Field and/or use of movements may be critical. The general rule of thumb with most lenses from top manufacturers has always been that the smallest marked aperture is weak, but that one or two stops up will give excellent performance. But like all rules some lenses will break them. One thing the Perez/Thalman chart highlights is that most lenses perform well at f16/f22 some are actually far better at f22, others may have better overall sharpness at f22 but better central sharpness at f16 or even f11.
In reality we are both nit-picking because it's how well a lens performs in actual use, as I said earlier I've never noticed or been able to spot any drop in performance of my LF lenses at f22 or even f32 and f45 with some of them. My Tessars & Xenar very definitely only become sharp across the full field at f22, and this as I said before is exactly what Zeiss have always said, and Chris Perez confirms.
I really don't know where the f22 figure comes from for other manufacturers/lenses but it's common across them all for 5x4 format lenses, and in general use by photographers around the world.
Interestingly someone once did a breakdown of the Apertures used by John Sexton, and no-one can doubt the quality of his images, the figures were:
For example, I looked at the technical data for the 49 photographs in John Sexton's Listen to the trees, done with a 4x5. The breakdown was as follows:
f16 5%
f22 30%
f32 50%
f45 20%
f64 5%
Those figures can't be quite right as they add up to 110% but they do give a fair indication that f32 is the most common aperture he's using followed by f22 and f45. I'd also guess that they aren't far off other peoples use as well.
Ian
