p.1 #2 · why these 2 Canon EF 70-200mm f-2.8L USM are different?
Welcome aboard FM.
No mystery as it is obvious from the pictures that the black rubber zoom ring grip on the lens on the left has slipped down out of position. Try pushing it back into place. There's probably some double sticky tape between the inside of the rubber and the outside of the white ring that may need to be replaced.
Oh . . . and also the lens on the left is set to "AF" auto focus while the lens on the right is set to "MF" manual focus.
p.1 #5 · why these 2 Canon EF 70-200mm f-2.8L USM are different?
The image on the left was taken from a closer distance; showing the effects of "proximity distortion", which some say does not exist.
Also, the lens on the left is set for AF, while the other is on MF. Plus, the lens on the left shows signs of more handing (pinhole chips, surface polishing), while the one on the right does not.
p.1 #6 · why these 2 Canon EF 70-200mm f-2.8L USM are different?
You can see the black rim where the ring has slipped backwards. With long time use the rubber grip ring can stretch and loosen up to the point where you can slip the whole ring off intact. This seemed to happen more often with the older lenses as opposed to recent models--I suspect Canon changed the rubber/adhesive formulation.
