I've been shooting on my C300 for a year now with only one problem that's happened twice to me. For some unknown reason I've lost iris control while filming on my workhorse lens of 17-55 2.8f. All other functions continue to to work but it becomes impossible to adjust exposure.

Restarting and reattaching the same lens seems to solve this problem but I'm wondering if anyone has experienced this or has any idea what the problem might be?

In both case the problem has been quickly and easily remedied but I'm wondering if this is a bigger issue that needs to be checked with Canon before my warranty expires.

Any ideas?

It's happened to me on the C100 maybe 3 or 4 times. Needed to restart.

It happened on various lenses. Not just 1.

This might explain what happened to me on a shoot in early December with a C300. I couldn't adjust the iris on the shoot early in the day and then it started working later in the day on the same lens. It was a rental camera and lens and I thought it might be a user error or a software glitch. Never came up with a specific reason.

Are you using the dial on the grip handle to control iris? If yes, make sure the mini plug from the handle cable if fully pushed in the C300. You really have to push it in and feel a bit of click, it's a safety feature to keep the connector in place....

But mine is happening on the C100 -- are you saying the same might apply? (Isn't the grip a different connection on the C300?)

At any rate, this has happened to me 3 or so times on the C100 where the F-stop suddenly reads "F--" instead of F1.8 for example.

Thanks Thierry but my problem with the loss of iris control occurred with both control wheels - the control dial on the grip and the control wheel on the camera body. Any other ideas as to what the problem is?

Tim,
I had that happen to me once when I first received the c100 and used a sigma 120-300 lens. My Canon lenses worked fine. Recently I tried the Sigma lens again and it is fine. Sometimes I think dirty contacts cause this. The same using a 5D MarkIII or other Canon bodies. Had that happen sometimes when shooting stills.
I just removed the lens, wiped the contacts with a soft lens cleaning cloth and put it back on the body and it worked fine.

Jerry Mennenga
Sioux City, Iowa