I bought canon EF 100-400mm f/4.5-5.6L IS USM lens from Delhi Grey market a year back. Since last 2-3 months I am observing some issue with its auto focus at higher focal length. At 100 MM there are no issue and it focusing the subject immediately.
At 300 or more, especially at 400mm the lens tries to focus but fails many times and takes more time to focus and some times do not focus. There is some abnormal sound like “ thuk, thuk” and it looks like the motor is moving it up and down in place of back and forth. At times I have to go back to 100mm than focus and then move to 400 mm while the shutter is half way pressed.
Can you please suggest what this problem is? Is grey market lenses in India are originally manufactured by canon? How to get it calibrated or repaired? Has anyone else faced such issue with any of the lens in past? What was the solution implemented?