in the past, I have been using the old model 28-70/2.8 for several years.
Then, the lens was dull at its compound lens inside and it needed to be fixed.
I have sent the lens to Canon Thai.
They replaced me with a new lens, 24-70/2.8 and I had to pay just around 20k Baht in exchange.
Very good service and I'm so happy about it both Canon services and the lens
