Subject: Philosophy of Exposure
From: David Mullen <mdmullen1@verizon.net>
Date: Mon, 19 Aug 2013 00:44:07 -0700
X-Message-Number: 10

I tend to think of Rec.709 as the print and log / raw as the negative, figuring if I can make it look good in Rec.709 but record log or raw, I know I'll have more information to play with in post. That's my general approach. I usually start out by checking my meter readings against how it looks on the monitor but after that, mainly expose by monitor except perhaps outdoors where your monitor is often not in a dark enough environment and your eyes are used to a higher ambient level.

To a lessor extent, the same problem exists at the other end, in extremely low-light environment where an LCD monitor starts to be the brightest thing in the room and you may tend to underexpose the monitor image to make it feel dark.

So to some degree there is a mental calculation that takes place if you relying on monitors in variable viewing environments. I can usually adjust my exposure tendencies to compensate, but I've had second unit work come back overexposed in day exterior scenes because they made the mistake of exposing until the image looked bright enough to see the action in a bright viewing environment (and this was after I warned them that this would happen.) This is where metering & exposure tools become more important.

It would be nice to see a waveform display of the log signal while monitoring a Rec.709 image to know exactly how much clipping is going on... but most camera set-ups seem to involve sending Rec.709 from the camera to the monitors so any waveform on the cart would be reading Rec.709.

You could send log to video village but then you'd need a Rec.709 conversion happening between the waveform and the monitor (I know, some monitors have Rec.709 LUT generators, just not the ones I can afford to rent.) Plus if I am using something like a ARRI Look File in the Alexa applied to the Rec.709 monitor output, then I can't really do the conversion to Rec.709 at the monitor unless I want to load special LUT's into a monitor that can take them. I could ask the camera assistant to switch the camera's monitor output back and forth between log and Rec.709 while I stand at the village but that's a bit time-consuming and awkward.

I don't find much value in seeing the waveform reading of the Rec.709 monitor signal if I am recording log or raw -- I can see clipping in Rec.709 with my own eyes on the monitor, so the waveform just tends to tell me what I can already see. I'd rather see a waveform reading of the log signal getting recorded.

I can't recall if the histogram in the Red cameras can be sent to video village and switched off and on easily at the village, since I generally don't operate... so having those exposure tools in the eyepiece or on the onboard doesn't always help me.

Anyway, once I get a sense of the how the monitor image tends to look relative to the exposure I should be using, I can rely less on my meter, which is one of the positive things about digital cinematography, to get away from being tied to the meter.

So I would say that my method is rather convoluted, I mainly come to rely on the monitor with occasional double-checks using various devices -- meters, waveforms, histograms -- just not on every shot. The main point is the feedback loop over time (if this is a long-form project), you check the footage again in dailies, in the editing room, etc. to see if your exposure technique is giving you good results, and sometimes you make adjustments when you find that your day work is a bit too hot or your night work is a bit too dark, etc. I also shoot tests before I begin to see how things look on the set versus later in a D.I. theater.

But again, this method of trying to work fast and not get bogged down thinking about exposure is one reason why latitude and wide dynamic range is important. When shooting film, I am pretty good at exposing so that I am printing within a narrow set of printer lights consistently... but I also know that within a range, the quality of the final image will turn out fine because of the latitude of film negative. With the newer digital cameras, the dynamic range is broad enough to give you similar flexibility.

Finally, the old saying "Know Thyself" can be applied to exposure technique, we know if we have a tendency to overexpose or underexpose in general so we can develop a technique to take that into account.

David Mullen, ASC
Los Angeles

Digital Cinema Society