Issue with Canon 100-400 USM lens

[Ashok Sorout]

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?

[Rajan Kanagasabai]

Hi

I've had the same "Hunting" issue with my lens. At the outer end, the lens needs more light and normally the 100-400 in poor light or a flat / no contrast subject, will result in the lens "Hunting".

This also has a direct reflection on the body that you are plugging this lens into. I have a 400D where the 'Hunting" issues are the highest (not just the 100-400, but the 150-500 as well), it is a lot better with the 40D, while the 5D Mark II has very very few of those issues.

I do not have any specific solution, other than switching bodies or resorting to manual focus, else kind of living with it. At times, i have turned off the IS while shooting off a tripod, which seemed to work.

However, what is strange is the 'Thuk Thuk" sound you mention.

hope this helps

regards
Rajan