28mm f2.8 SMC Pentax-M Diffraction ?

I found a print in my files taken at Birling Gap, East Sussex (UK) where I had used the minimum f22 on my 28mm f2.8 SMC Pentax-M lens and on a 16x12" print it is not really 'Sharp' anywhere, probably due to 'diffraction'. I used an ME Super, Grad Grey Cokin Filter, tripod and that Kodak 400 ASA C41 B&W film which I processed myself -- maybe the FILM is not very sharp either . It LOOKS SHARP on THIS size photo .
Print scan : HP Scanjet 4570c + Vuescan Pro+ PhotoShop 7

Looks good to me, I like it.

To be honest I think you might need a tilt-shift lens to get a shot like that properly sharp from foreground to background.

I like the shot.

C41 black and white film isn't as crisp as silver-rich conventional emulsions. Ideally this one could have used Ilford Pan F (ISO 50) or, even better, Kodak Panatomic-X (ISO 32).

Yes - next time if I ever go back I will take my Mamiya Press Super 23 with tilting back movement and use the 'Scheimpflug Rule ' !!
PS : I was GIVEN three cassettes of Kodak Panatomic -X dated 1989 but I used them all up already !