Jack & Bob..Thanks very much.
Does it mean that the only ways I can achieve DOF from few feet to infinity for the IQ 180 with insignificant diffraction are T/S (probably from a Tech Camera) and focus stacking?
Tim Fitzharris, an award winning nature & landscape photographer, published a lovely book "National Audubon Society Guide to Landscape Photography" in 2007. He used Mamiya with non-digital (even manual ones) Mamiya lenses and Phase One P25 throughout his book with f/16 and f/22. His pictures looked fantastic. He also claimed they looked great on his big prints.
His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?
I got myself a tech camera and use tilt in I would guess 50% of my images. Tilt often provides you with better options, but it depends a lot on your style. If you have high stuff close (tight forest scenes etc) tilt don't help much, but if you often do open scenery tilt helps a lot. Personally I think focus stacking is a mess, there's always some artifact in there, and I prefer to make one shot images. I go f/32 + some pieces out of focus before I consider focus stacking, but that's my personal decision.
But as discussed above having the sharpest possible picture is not that important for smaller sizes and relaxed viewing conditions, and even if viewing conditions are such that one can see that the image is not tack sharp few cares. Image content is all that matters.
Still as a photographer one may like to make sharp pictures and because one appreciates it oneself. If it weren't for that (and other subtle quality aspects) I think digital medium format would be dead by now.
Concerning tilt vs not having tilt some have a shooting style where you focus at a main subject and you consider that other parts in the picture is a bit less sharp is an advantage, give it a subtle depth. Therefore some landscape shooters can have an IQ180 and never use tilt. Using tilt and shift is for me an integrated part of my photographic process, I simply enjoy using it and it do give me subtle image quality properties I like, but the main reason I use them is simply because I enjoy making pictures "view camera style", it's fun.
There's an interesting aspect about diffraction, which is that it is not a hard limit. This means that if you shoot f/22 with a 80 megapixel back you get slightly more total resolution than f/22 with a 20 megapixel back, but the more diffraction there is diminishing returns. I recently saw an interesting print comparison test, and then a 36 megapixel D800 f/22 carefully deconvolution sharpened and contrast corrected produced as good print result as a 20 megapixel camera at f/8 (also sharpened)! Extremely low noise levels (as the D800 has) improves the possibility to deconvolve as that type of sharpening increases noise.
P25 is only 22 megapixels, the pixels are huge, 9 um. This means that on a pixelpeep level you get less affected of small apertures, so f/16 and even f/22 does look quite sharp at 100% on screen. But as stated above, f/22 on an 80 megapixel IQ180 + sharpening would still make an even sharper print, although it would look fuzzier at the pixelpeep level.
People were happy with 22 megapixels back then, and from an artistic standpoint it is of course enough. But if we have paid tens of thousands of dollars to get an IQ180 rather than a second hand P25 for a couple of grands we surely want to make as sharp images as that IQ180 can do, even if most of our audience would not notice or care.