I have an EOS 5d Mark IV camera with a Tamron maco. It's been working great for the last year I've been using them. In the last 2 days, as I'm photo'g still shots, it acts like it's having trouble focusing. I get a "clunk" sound following by "chattering" with a AI servo flashing in the viewfinder. I've search the web for any hints, cleaned the lens connection, then reset everything back to default settings. It's still happening. Any thoughts?
" I've ..., cleaned the lens connection, then reset everything back to default settings"
Yeah, neither of those two things will help. Cleaning the contacts is just a feel good I did something. Actually you can do more damage to them than any benefit you get. Since it is a Tamron resetting the camera probably won't help any more than just turning it off and back on.
If I were you, I would call Tamron. It sounds like a total lens failure is in your future. Canon can not help you with this and would instruct you to stop using the Tamron, so call Tamron.
Quite possibly a failure, but 1. does it do it in Single Shot, 2. when in AI Servo are you at a distance where it should focus (i.e. not to close?). AI Servo never locks focus like Single Shot; it keeps actively calculating on the subject.
Does the lens has image stabilizer or vibration control feature? If so, switch it off (if its on).