I've been using the Tamron 24-70 with my C100 for many months now, almost entirely in manual mode with my cameraman pulling focus for me as needed. Last night we decided to let the autofocus do the job on a starkly lit close-to-wide dolly shot. With the f-stop set to 4, we started seeing an issue where the autofocus mechanism would go a little crazy and then the lens would suddenly drop a stop. Happened when the camera was locked or moving, with VC on or off. The camera op finally fixed the problem by opening the lens all the way to 2.8. After that, the problem stopped occurring.
I haven't done any additional testing since last night, but has anyone else experienced a similar issue? The dropped stop is the weirdest thing. I've had many lenses hunt for focus but I've never experienced an impromptu f-stop change.
I haven't done any additional testing since last night, but has anyone else experienced a similar issue? The dropped stop is the weirdest thing. I've had many lenses hunt for focus but I've never experienced an impromptu f-stop change.