As far as I know, "sweet spot" of the lens should refer to the best/sharpness quality you can get from the lens is its focal length + f/stop.
Care to share with us how to test it out?
Is the sweet spots varies from camera to camera eventhough using the same lens model/built? or only refer to the lens model itself?
say, EF-S 18-55mm f/3.5-5.6, EF 50mm f/1.8, Sigma 70-300mm f/4-5.6 APO Super Macro II. what are their sweet spots
Thanks in advance.