Jungie wrote:
I got this new lens hood from Ebay and I don't know the use of something that came attached to the lens hood. I'm using red arrows to point the strange item I don't know the use...
Canon's lens hoods mount on the bayonet tabs on the front of the lens, and thus the shape of the hood is always properly aligned.
This third-party lens hood is designed to screw into the filter thread. Since it's hard to determine where the hood will end up when the threads bottom out, they provide a lock ring. You screw the lock ring up tight against the hood, screw it into the lens until it bottoms out, loosen it until the hood is properly aligned, and then tighten the knurled lock ring down onto the lens.
Rick "who prefers the more expensive Canon hoods that don't use the filter threads" Denney