I have this lens for almost 12 years (was purchased in 2006). The tighten/loose ring did not work long time ago.
Since this lens is old (but still function very well), I decided to fix it myself. In the same time, I hope I can do a good service clean myself.
I put down all my work in the following two youtube videos:
This is the part that how I fix it:
This is the previous part that how I open the front lens element:
The opening of the front element is the toughest part. Those screws are really tight. If stripped then can follow this video.
I used the power drill to open the front element. And at the back of the video I introduced a way to put everything back in order.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.