I come from the North of England. My friends are trying to teach me to speak American English, but I'm not a fast learner. After four years I'm still failing Gushing 101. 'An OK lens' is quite a compliment from me, and means that the lens does exactly what it is supposed to do. The 80 mm Super-Symmar XL and 28 mm Leica Summicron-M are also OK lenses, for example. If you want a 28 mm shift lens then the PC-Super-Angulon is an excellent choice.
Extract from my English - American phrasebook:
"An OK lens" = "No flaws to speak of"