Hi,
First of all, I'm not a videographer... so hopefully someone who is will jump in here with an answer, if I'm way off base.
What I'd look at first is - if you have Exposure Simulation on - are your settings greatly over-exposing, so all you are seeing is a totally blown out image on the LCD monitor? That's the first thing I'd suspect. Reduce your ISO and/or stop the lens down to see if that gets you back into the usable recording range of the camera.
If you are trying to use a large aperture to render shallow depth of field... In order to use a large aperture outdoors in normal daylight, it's often necessary to use a fairly strong neutral density filter. The camera simply doesn't have a low enough ISO to allow for large lens apertures to be used in brighter light conditions.
If that doesn't help, I really don't know.
I might try resetting the menu selection and custom functions to the defaults.... Or maybe it would help to "reboot" the camera (I don't know how that is done on 6D... on other cameras it's done by removing both the main and the memory battery, but 6D's memory battery isn't user accessible, AFAIK)... Or, maybe it would help to reinstall the firmware.
Honestly, none of these are likely to help. But they are all free and easy to try. And some times they do help... resetting something that's incorrect, or removing some instructions that are stuck in the camera's memory, or correcting corrupted firmware.
First thing, though, is to check if it's simply extreme over-exposure. If that's happening, I imagine Exposure Simulation would show it, on the LCD monitor.
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM
