Is exposing C-log different than usual?

[Walter Brokx]

Since I'll be shooting with a C300 in 2 days from now I wonder whether there are different rules than usual when I use C-log instead of a normal colorprofile.

What is the right way to use (and expose) C-Log?

And is grading different too or not?
(I usually use Colorista and Magic Bullet Looks (not just the presets) to grade my EX1R-footage while using waveforms.)

[Alister Chapman]

Yes. When shooting log you have to consider that in order to record the increases dynamic range, each stop of exposure is allocated a very similar amount of data. But as each extra stop is a doubling of brightness range there is in effect more and more image compression occurring as the image brightness increases. For maximum grade ability, you don't want all your picture information up in the highlights. So generally with a log curve you will underexpose slightly compared to a standard gamma. The norm is to use a mid grey card and expose it so that it is at 38% and reflected white should be somewhere around 70%. Reflected white at 70% then allows headroom for direct light sources like the sky or reflections off shiny surfaces.

That's the theory at least, in practice things will vary from scene to scene, but the primary concern is to not overexpose and to keep highlights well controlled.

[Graham King]

I'd also like to hear form others on this. I hear you on the grey/white card method but is there an easier way to get perfect exposure on the fly without a card in the scene? On the EX1, I set zebra 1 to 56 IRE and exposed for zebras on the brightest part of the subject's face (except dark skin people) and the results were always great. But you can't do that with the current C300 firmware. And I also don't like how zebra 1 & 2 look so similar. On the EX1, zebra 2 was much thicker which was fine because that was overexposed anyway.

[Robert Sanders]

Originally Posted by Alister Chapman

Yes. When shooting log you have to consider that in order to record the increases dynamic range, each stop of exposure is allocated a very similar amount of data. But as each extra stop is a doubling of brightness range there is in effect more and more image compression occurring as the image brightness increases. For maximum grade ability, you don't want all your picture information up in the highlights. So generally with a log curve you will underexpose slightly compared to a standard gamma. The norm is to use a mid grey card and expose it so that it is at 38% and reflected white should be somewhere around 70%. Reflected white at 70% then allows headroom for direct light sources like the sky or reflections off shiny surfaces.

That's the theory at least, in practice things will vary from scene to scene, but the primary concern is to not overexpose and to keep highlights well controlled.

That's a great summarization. Cheers, Alister.

[Alister Chapman]

56 IRE for skin tones with standard gamma? That's quite low for a standard gamma, it's more common to use 65 IRE for skin tones. Is that a typo?

With C-log, skin tones I would place bright skin tones around 60IRE.

[Graham King]

Nope not a typo. I got that number from an unusual source. It's what Marshall recommends for skin tones when using their false color feature. Looked great to me so I stuck with it.

So 60 in C-Log sounds good to me. Except the C300 only goes down to 70. :-/

Edit: 70 on zebras that is

[Walter Brokx]

Thanks for the quick and helpfull replies!

Since I'll be on a very tight schedule, I'm considering using a normal gamma instead of C-log.
(Practising C-log exposure has to wait, I guess ;-) )

[Colin McAuliffe]

i really do hope canon updates firmware so we can get zebras below 70

[Nigel Akam]

I've emailed pro support up here in Canada about the zebras under 70, and was told it would be forwarded to the correct people. Probably a good idea for everyone to do the same in their region.

Also brought up having selectable display of the SDI. For example only sending TC to the client monitor, instead of everything on the screen.

[Colin McAuliffe]

yeah,

i keep calling about once a week asking for a few things...most of them correctable with firmware.

I also really want them to make it so that when you split one source of audio to both channels, you can control the levels of the 2 channels seperately.

as it is now, when you split the one source the two channels are locked at the same volume.

[Graham King]

I can't seem to assign two different functions to the wheel on the hand grip and the lower wheel on the body. Has anyone been able to do this? I would request that in a firmware update if it's not currently possible.

[Colin McAuliffe]

yes, thaat is my other request. i want to have iris on handle and ISO on the body

[Graham King]

That's exactly what I wanted to do!

[Colin McAuliffe]

yup....would probably save me an hour over the space of a year...

[Graham King]

I assigned ISO to button 1 so I can't say it'd save me an hour per year but it would be nice. Actually, if it could be assigned to color temp I'd probably do that as I do a lot of run & gun.