problem with auto focus...pl help!

[Kaling Dai]

dear all
i bought a tamron lens 150-600 mm f/5-6.3 a couple of weeks back & tried it on canon 5dIII. lens in question doesn't seem to auto focus when zoomed in beyond 300 mm. it just makes some rattling sound & refuses to focus. can anybody suggest any solution to it? regards. Kaling Dai.

[Sabyasachi Patra]

Tough situation. Are you able to manually focus the lens beyond 300mm? Just check if something is stuck in the lens which makes autofocus difficult.

I don't prefer third party lenses. Long back I had a problem with a Sigma 300mm f4 lens which stopped behaving well with a new Canon camera. I then had to send it to Canon Singapore and then from Singapore to Japan to correct it. That was more than 10 years back. However, the same issue of software incompatibility remains between third party lenses and new cameras. For example several new sigma lenses don't autofocus with the new dual pixel autofocus of Canon C100 camera. With this background, I want to ask you to test the tamron 150-600 lens with older canon cameras 7D, or 5D II or any of the previous generation cameras. If it works well, then you know the problem.

[Kaling Dai]

Thank you, Sabyasachi for your prompt response & advice. yes, manual focus is possible even at 600 mm, i have tested it on 7D as well & the result is the same. so i contacted Tamron master service centre at Gurgaon, has instructed to send the lens there for repair or so.