Almost as sharp as the f2.8 IS variant but at half the weight, while CA is also marginally better (less elements?)
Adding a Kenko 1.4x teleconverter has neglible effect on the sharpness although CA begins to climb. Neither the Kenko or the Canon 2x teleconverters are good options, but drop the aperture to f11 (canon 2x) and you get something workable, albeit for bright conditions only.
Unfortunatley, I sold the lens before I got a Canon 1.4x teleconverter, so to speculate, it could be a good combination if you need that extra 80mm.
Almost as sharp as the f2.8 IS variant but at half the weight, while CA is also marginally better (less elements?)
Adding a Kenko 1.4x teleconverter has neglible effect on the sharpness although CA begins to climb. Neither the Kenko or the Canon 2x teleconverters are good options, but drop the aperture to f11 (canon 2x) and you get something workable, albeit for bright conditions only.
Unfortunatley, I sold the lens before I got a Canon 1.4x teleconverter, so to speculate, it could be a good combination if you need that extra 80mm.