to be fair most lenses should perform nicely at f8-9... its wide open they struggle
The tamrons strength (although apparently not on nikon or canon depending on what you read) is its insane sharpness at f2.8, when you get a good copy!
i have one purchased recently (on pentax mount) and it truly is incredibly sharp and well rendering... focus isnt too shabby for a screwdrive either...
QC is hit an miss from what i read and generally more so with N or C due to the electronic motor focus drive they have to have...
Its a monster lens tho! Suits me down to the ground....
Steve
