Tele lenses in c. 85mm-300mm range often reveal slight oddities when shooting
houses a few hundred feet away (The horizon shots may look fine, but the
out-of-focus areas beyond the houses may show differences even when the
in-focus stuff checks out well [if it does].). Since it is so hard to get the
lens parallel to the subject when close, I shoot a flat detailed target at
an angle so I can see the line of sharpness, and run it to opposite corners
(again, the reference is the center at f5.6). David