MK IV Focus brightness during recording

I am an absolute newby to video on this MKIV so let me apologize in advance for some simple questions. I need to shoot a short video and am struggling with regards to focus.

When I auto focus during recording, the live view display (and the recording) get about 2 stops brighter until the focus is acquired. Then the brightness returns to normal.

What is that about?

Thanks for the help.....

Basiclly it is either opening up the aperture all the way (to make autofocus easier/possible) or bumping up the sensitivity for the same reason. When the picture is brighter it makes the contrast detection algorithm not have to work as hard to find focus.

my suggestion: either manually focus, or focus beforehand.

JPM Photography wrote in post #11885029
Basiclly it is either opening up the aperture all the way (to make autofocus easier/possible) or bumping up the sensitivity for the same reason. When the picture is brighter it makes the contrast detection algorithm not have to work as hard to find focus.

my suggestion: either manually focus, or focus beforehand.

Exactly, well said!

Pre-focus your scenes. That's what most people do nowadays with HDSLRs.

Or if you are pro enough, manual focus during recording the footage. There are tools to aid you on this like a monitor, a basic stable rig, and follow focus too.

Contrast-based focusing is all that the Mark IV has under Live View or video (which is why you saw the brightening). Basically either pull your own focus (with a follow focus or just manual on the lens) or auto focus what you want before hand. I choose to pull my own focus because it's almost second nature to me by now, but some don't want to do it that way.