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LogC Shooting


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#1 Paul Prinz

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Posted 05 September 2014 - 03:19 PM

Hi ,

I'm working with an Arri Amira and we want to shoot in LogC of course. So i heard that most of the people just shoot in LogC but they don't exposure in the correct way to use really the whole Dynamic Range.
When i remember shooting film i always used a grey card and spottet it with the light meter.
Should i do this shooting in LogC also ? If i have to decide to over or under expose a little , better over i guess ?

Maybe someone has experience shooting LogC and want to share with me clear.png

best regards
Paul

 


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#2 John E Clark

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Posted 05 September 2014 - 06:31 PM

 

 Hi ,

I'm working with an Arri Amira and we want to shoot in LogC of course. So i heard that most of the people just shoot in LogC but they don't exposure in the correct way to use really the whole Dynamic Range.

 

I don't have access to an ARRI anything... but when I was researching how to calibrate one's effective ISO values for any 'digital' camera, I did run across some articles on ARRI Alexa and what principles were involved in determining exposures that allowed for the full dynamic range of the camera to be recorded/available.

 

Here's an article:

 

http://provideocoali...w_you_use_it/P2

 

This method requires that you have the ability to display the a IRE waveform, and the step test target.

 

It seems that a 18% grey card reading shoud be, from the article according to ARRI, around 38% IRE for LogC recording. The author of the article seems to want to place the 18% grey card at 45-50% IRE...

 

So, one would have to test to calibrate meter reading with its ISO settings, camera ISO setting, to IRE output based on the 18% grey card. (I declined getting to 'is the 18% grey card really 18%...).


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#3 Satsuki Murashige

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Posted 06 September 2014 - 12:18 AM

With the Arri Alexa (and now Amira), standard practice is to record Log C to the SxS cards while viewing a Rec.709 LUT in the viewfinder and SDI output. So while you are recording a flat desaturated image, you are lighting and exposing to a picture with normal contrast and color saturation.

There are a few extra stops captured in the highlights and shadows that you won't see when shooting this way, so to check what you're actually recording you can toggle between Log C and Rec.709 with one of the assignable user keys and check your waveform monitor.
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#4 David Mullen ASC

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Posted 06 September 2014 - 05:03 PM

Assuming your subject has a wide dynamic range to begin with, you're going to be recording the widest dynamic range possible on the Alexa (14.5 stops) even if you misexpose (except for some unusual situations) it's just that your balance between highlight and shadow detail will shift one way or the other depending on the direction of your misexposure. At 800 ISO you basically will have an even amount of over and under information.

As mentioned already, you record Log-C but monitor in some form of Rec.709 (custom or standard) knowing that more stops of information are being recorded than will be visible on the monitor, similar to the gamma difference between a negative and a print. In other words, with the Alexa, you can expose it like 800 ISO negative film and get decent results, it's not a totally different way of exposing compared to shooting film, which is one reason why the Alexa is so popular.
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#5 Israel Romero Ramírez

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Posted 24 November 2014 - 06:26 PM

use the arri interactive interface... set the viewfinder to rec.709  and internal or external to log c.  


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#6 Larry DeGala

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Posted 01 August 2015 - 05:23 PM

I was impressed that there's a whole lot of information in highlight areas that seemed blown out.  And there is much information in the shadows as well.  Match that with beautiful glass.

I do remember exposure settings for negative film. In news applications, there was reversal film for news applications. Rule of thumb was shoot Standard Def video like reversal.  It has been a pleasure to shoot a stop or two over for digital acquisition.  Nostalgia.


Edited by Larry DeGala, 01 August 2015 - 05:27 PM.

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#7 Tom Yanowitz

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Posted 06 August 2015 - 12:38 PM

One of the best tools for exposing with Arri cameras for me is the False Color for extreme highs and shadows (a bit less interesting for midtones as you don't HAVE to expose skin tones in pink or whatever to get what you want).

Where to put middle gray isn't as important as people think it is I think, especially if grading is part of the workflow (which it is if you record LogC)

 

One thing to note is that waveforms, histograms and even false color adapt to the kind of display you're outputing so you have to look at those tools with the recorded mapping (log or rec709 or looks) displayed.


Edited by Tom Yanowitz, 06 August 2015 - 12:39 PM.

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