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Sony XDCAM PMW-F3 CineAlta
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Old December 16th, 2011, 01:55 AM   #1
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S-Log Cuts off at 106 IRE

After seeing what Alister said and then checking my own footage, I wanted to look further into why my footage only went to 106. So, earlier tonight, I pointed the F3 at a light and the brightness level said 106. Then, I hit my assigned button 6 to turn on a LUT (HG40 preset) and the brightness level went to 109.

Is this normal for S-Log or a bug in their firmware? (using v1.2 and prior footage was with v1.1)
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Old December 16th, 2011, 10:12 AM   #2
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Re: S-Log Cuts off at 106 IRE

Deleted post. Changed my mind.
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Old December 16th, 2011, 11:37 AM   #3
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Re: S-Log Cuts off at 106 IRE

It really doesn't matter to me personally whether it maps to 106 or 100, or 90.

It's getting another 2.5 stops of dynamic range squeezed in there (at least). To use the phrase "cuts off" implies there's premature clipping of the signal, and since there's (empiracally measured) so much more dynamic range there to be had, I'd say it more likely it was a chosen mapping point for some reason.
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Old December 16th, 2011, 11:49 AM   #4
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Re: S-Log Cuts off at 106 IRE

Incidentally, the Alexa, when in Log-C, maps black to somewhere around 30IRE and white to somewhere around 80.

Seems bit-wasteful, but I suspect since Log-C is recording to 12 bits (ProRes 444), they're using the available codec bits in the best way they see fit.
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Old December 16th, 2011, 01:44 PM   #5
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Re: S-Log Cuts off at 106 IRE

I should have added that some of us believe Pro Res clips at 106 which was based on using S-Log footage. Now that I know its the F3 cutting off at 106, maybe Pro Res doesn't actually clip at 106....
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Old December 16th, 2011, 05:08 PM   #6
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Re: S-Log Cuts off at 106 IRE

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Originally Posted by Steve Kalle View Post
I should have added that some of us believe Pro Res clips at 106 which was based on using S-Log footage. Now that I know its the F3 cutting off at 106, maybe Pro Res doesn't actually clip at 106....
Right. I know. But the original question implies that if the highlights aren't hitting 109, then something is wrong. ("is it a bug...")

So I guess the answer is, it's normal, and it's not necessarily a bad thing.

Every computer program handles that info as it comes in anyway, but allows you to scale, so it's kinda here nor there, unless somehow wasting the top few digits (27 levels, to be exact) on a 1024 scale really gets your goat. And if you're seeing 106 vs 109 via software scopes, all bets are off anyway. Those things are all over the place.

There's a good chance that if you light was brighter, you could have pegged those last 3 IRE, you know :-) S-Log is kinda like that.
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Old December 16th, 2011, 05:17 PM   #7
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Re: S-Log Cuts off at 106 IRE

Hi Nate.

After Alister initially pointed out the 106 Pro Res thing, I connected the F3 to a 24" Sony LUMA and a 17" Pan 1760 and both stopped at 106.

So, the answer is that its normal.
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