« on: February 23, 2014, 09:24:27 AM »
I have some experience with anti-reflection coatings in the Ophthalmic (ie: eyeglasses) industry.
If anti-reflection coatings are not perfectly applied, they do indeed seem to peel off over time without the consumer doing anything wrong. The companies that make lenses for eyeglasses have had a lot of problems with this ever since AR coatings became popular about 20 years ago. I think this problem is pretty rare in cameras and other optical instruments, because I have never seen it, but it seems likely that a batch of front elements was not properly coated.
As far as I know, there is nothing the consumer can do to make the AR coat start peeling without doing something drastic that would damage other parts of the lens in some obvious way. It certainly is not due to any kind of cleaning and it is not caused by scratches. A defective coating is really easy for me to spot because I've seen hundreds, but a camera tech probably hasn't seen many.
My guess is that either the machine that applies the coating to a batch of lenses in a vacuum chamber was not operating properly or the lenses were not properly cleaned before the coating process. No way for us to know how big a batch is or how many batches were affected.
I don't think it would be appropriate to recall every one of these lenses, since the number of lenses affected is probably small. In my opinion, Canon should issue a warranty notice like they did for the improperly secured mirrors on the early 5D classic. If somebody sends a lens in with a defective coating, it gets fixed for free regardless of warranty status. This is clearly a manufacturing defect. Technicians should be told what a defective coating looks like so that they don't blame the customer. It is really easy to spot a defective coating, it's the one that looks like it is peeling off!
What Canon chooses to do about this will tell us a lot about their commitment to customer service. It will either make them look good or it will make them look bad.