Push-AutoFocus without exposure change

[eyeland]

Like most people, I don't use auto focus while recording video.
I have however, recently been in a few scenarios where is was handy.
These days I am doing alot of run-and-gun event coverage (sometimes in extreme low light) and once in a while - for the right kind of scene - it seems usable to me to let the camera auto-focus. If it hunts alot, so be it, I'll probably edit it out and thus, this method will not be used when something important is going on.

Maybe I am just addicted to having all options (even the ones I woun't be using) but I can't help thinking that it would be interesting to experiment with push-AF if it wasn't for the horrible exposure changes.
The focus hunting is one thing (on a very rare occasion I have even used it to give an explicit gonzo-PoV effect) but the exposure changes basically always makes the shot useless - even in the rare ocasion whenre the AF actually nails focus without much hunting.
Sometimes I catch myself pushing AF after pulling manual focus just to see what the camera WOULD have chosen (When using AF after MF, often the AF doesn't hunt much)
It seems that the camera gains up to 12800 ISO when AF is activated (at least it seems that the exposure fluctuation does not happen @12800)
So, with the danger of being regarded as an absolute cinema-nuub and/or just silly, is it at all possible to deactivate the AF-gain (or whatever is happening)?

[engardeknave]

Uh, isn't that just a matter of setting your camera to a manual mode, or putting metering and AF on different buttons?

[a1ex]

Try gradual exposure. If that won't help, I'm not sure what else will...

[eyeland]

Uh, isn't that just a matter of setting your camera to a manual mode, or putting metering and AF on different buttons?

If you managed to get it to work, care to give a detailed description?
My camera is always on manual when shooting video, and AF is always moved from shutter button to AF-ON button. I don't seem to find an option for getting AF-ON to not auto-meter though... Only options in custom functions pertaining to AF-ON button are: "Metering and AF start", "AE lock", "AF stop", "FE lock" "AE lock (hold)" and OFF. Holding down a button assigned to AE lock while pushing AF makes no difference either.

Try gradual exposure. If that won't help, I'm not sure what else will...

Gradiual expossure (which BTW is such a nice feature) makes no difference either way. Camera still gains up or down dramatically when AF is activated.

Starting to wonder if I am totally missing something.. Seen alot of talk that "AF hunting" makes AF useless for video, but that particular seems insignificant compared to the exposure shifts. Maybe I'll just have to wait for someone to stumble on the relevant code?

[engardeknave]

There's probably something I don't know about going on. I don't shoot video.

[a1ex]

Gradiual expossure (which BTW is such a nice feature) makes no difference either way. Camera still gains up or down dramatically when AF is activated.

Just tried on 5D3 and 50/1.8 and it's working. The image changes the noise pattern a little, but overall brightness stays the same.

[ItsMeLenny]

The reason why the exposure changes is so the camera can focus better.
If the picture is too dark it will hunt forever.

[eyeland]

Just tried on 5D3 and 50/1.8 and it's working. The image changes the noise pattern a little, but overall brightness stays the same.

Which build? In all the builds I have tried, result is the same regardless of "Gradual exposure" setting.

[a1ex]

Shouldn't matter; this feature was coded months ago (or maybe one year?)

Can you upload a video?

[eyeland]

Shouldn't matter; this feature was coded months ago (or maybe one year?)
Can you upload a video?

Will do as soon as I get time - probably will be in a week or so as I am flying home for xmas after finishing a deadline Thanks for looking into it.