Best Practices. Obtaining Proper Exposure. Share your methods please.

[Sascha Rossier]

d'accord ... i definitely don't want to argue about a single word, since as a swiss guy, my english doesn't allow for these subtle gradations anyway ;-) i just wanted to give Arnold a few useful answer to his questions. So let's not use "Native" and instead i'd put it that way: At ISO320 the monitor shows just about a pretty true representation of the RAW-Signal and therefore is a pretty good place to be if you need to judge the image you are recording. Whereas at ISO 800 the Monitor "lies" to you because it actually shows a brighter picture than recorded. (Of course this is exactly to make you stop down a little which actually makes you protect the highlights)
It is also worth knowing that the Histogram represents the image with your ISO setting included. But The Goalposts and stoplights don't get affected by the ISO-Setting. So if you want to "Expose to the right" i think its best to judge the histogram that represents the RAW-Image as closely as possible i.e. @ISO320.

[Sascha Rossier]

Even at 800 I doubt I'll come close to lighting the basement enough to avoid clipping on the low end. There is going to be a lot of black. I'll get my talent and immediate surroundings up but some areas will be dead black. Do I need to worry about this?

That's an artistic choice. Normally you want to have at least some detail in a good portion of the picture, even if its just some gradations of darkness (;-) because dead black just looks ... well ... black and therefore pretty flat. so if you manage to break up the dead black with some source of light (not lighting the whole basement) but maybe take a 650 and shoot i through some blinds or some leafs on a wall in the back to give some streaks of dull light this would add detail and if put in the right place even add depth to the shot. So short answer. The camera won't complain if you have 80% of the frame pitch black (as long as you don't try to bring back some details in the black areain post) ... but usually big flat areas don't look very cool (no mather if its black, white, grey ...)

[Noah Yuan-Vogel]

d'accord ... i definitely don't want to argue about a single word, since as a swiss guy, my english doesn't allow for these subtle gradations anyway ;-) i just wanted to give Arnold a few useful answer to his questions. So let's not use "Native" and instead i'd put it that way: At ISO320 the monitor shows just about a pretty true representation of the RAW-Signal ...

It has been established, though, that it is not particularly indicative of anything that "RAW view" happens to use the ISO320 curve, it is not somehow a more "true" representation of the RAW signal. Graeme confirmed this when I asked him about it. The RAW signal is linear light and would look nothing like anything you are used to seeing and would look extremely dark if shown to you un-gamma-corrected. Even ISO250 as you say "lies" to you because it shows you a brighter picture than recorded, but that's because you aren't recording pictures, you are recording linear sensor data that doesn't look like much until a curve is applied, whether its RED's ISO320 or ISO800 curve.

My theory about why RAW view happens to use the ISO320 curve is that when RAW view was first designed, redspace was the gamma curve in use and was designed around the ISO320 curve. Back then, RAW view was more important to keep track of because redspace did not hold the whole DR of the sensor for other ISO curves, and increasing ISO would sometimes make highlights blow out that were not blown in RAW or in ISO320, so it was important to be able to switch quickly back to that initial ISO320 5000k setting since it would show you what was really blowing out and be reminded how hard you are pushing your B channel when you are shooting at 3200k for example. Now this is less important because new REDGAMMAs are designed mostly around ISO800 and scale much better throughout various ISO settings, keeping the whole range in there, so now it is not so useful to have a quick switch back to ISO320.

[Arnold F.]

Noah and Sascha, thank you for reviving this thread for me. Let me replay in my own words what I think I'm hearing and please tell me if I have it wrong:

The sensor has one sensitivity, 320 ISO, and all others can be thought of as "virtual" ISO's. No real gain adjustments can be made in-camera like they can in my HVX or 5D. Regardless of what "ISO" I shoot at the sensor accepts it at 320. If I choose 1600 I am, to a degree, pre-choosing that gain/ISO in post because all other exposure parameters (shutter speed, aperture, etc.) were chosen based on that ISO. ISO is "chosen" on set and "confirmed" (with some latitude available) in post. The histogram will change with ISO changes based on the assumption that that ISO will be chosen in post. However, what remains the same is that a gain increase, although now in post, still results in added noise like it always has.

Is all of that correct?

It's hard to imagine that all the very dim, subtly lit shots I've seen made with the Epic and Scarlet were lit brightly enough to expose at 320 ISO. Take, for example, that one Jim posted in the Recon thread of Leonardo DiCaprio. I know I don't have the skills to throw 3K of light onto a scene (in order to keep it at 320) and make it look like it's lit by candle-light. In addition, I don't want to shoot wide open. I don't want the compromises in sharpness many lenses make wide open and I don't yet have the skills to work with the micro-thin of depth of field that results.

It has been established, though, that it is not particularly indicative of anything that "RAW view" happens to use the ISO320 curve, it is not somehow a more "true" representation of the RAW signal. Graeme confirmed this when I asked him about it. The RAW signal is linear light and would look nothing like anything you are used to seeing and would look extremely dark if shown to you un-gamma-corrected. Even ISO250 as you say "lies" to you because it shows you a brighter picture than recorded, but that's because you aren't recording pictures, you are recording linear sensor data that doesn't look like much until a curve is applied, whether its RED's ISO320 or ISO800 curve.

My theory about why RAW view happens to use the ISO320 curve is that when RAW view was first designed, redspace was the gamma curve in use and was designed around the ISO320 curve. Back then, RAW view was more important to keep track of because redspace did not hold the whole DR of the sensor for other ISO curves, and increasing ISO would sometimes make highlights blow out that were not blown in RAW or in ISO320, so it was important to be able to switch quickly back to that initial ISO320 5000k setting since it would show you what was really blowing out and be reminded how hard you are pushing your B channel when you are shooting at 3200k for example. Now this is less important because new REDGAMMAs are designed mostly around ISO800 and scale much better throughout various ISO settings, keeping the whole range in there, so now it is not so useful to have a quick switch back to ISO320.

[Noah Yuan-Vogel]

The sensor has one sensitivity, 320 ISO, and all others can be thought of as "virtual" ISO's. No real gain adjustments can be made in-camera like they can in my HVX or 5D.

More like all ISOs including ISO320 can be thought of as virtual ISOs, each with its benefits and tradeoffs, but all with essentially the same dynamic range.

[Arnold F.]

Can you comment on my other interpretations?

Is there any reason why I can't set my ISO to 1600 tomorrow and just try to watch clipping on both ends? How will the result be different than shooting at 320. All of my lenses would have to be f1.2 or faster to shoot in a dark room at 320.

More like all ISOs including ISO320 can be thought of as virtual ISOs, each with its benefits and tradeoffs, but all with essentially the same dynamic range.

[Blair S. Paulsen]

The in camera ISO setting changes what you see in the monitor path and what the image looks like when first opened in post, therefore:
If the levels on the monitor and in the RGB derived histogram lead you to change your exposure then they have indirectly changed your results.
If your only practical way to communicate your intentions to post is via the metadata (like ISO) then it can influence post choices and by extension the final look.

Exposing to the right while staying out of the clip is a solid formula.
The notes about the way a linear light container assigns available bits is a critical bit of understanding.
Adding a bit of fill light to dark areas and then crushing them back down in post is an excellent way to reduce noise in the shadows.
Setting the ISO at 800 has pitfalls as noted, but IMO is the best option when working on a collaborative set with clients/producers - especially if the monitor they are viewing is in an environment with high ambient light!

For digital sensors instead of ISO, I prefer to look at the signal to noise ratio (S/N) and keep an eye on "feeding the blue beast". 99% of the time, as long as there is a decent amount of exposure in the blue channel, noise on the MX chip is minimal.

TIP: Even though it is an "artificial" representation of what you are putting in the RAW data set, I use the RGB derived histogram as a critical tool in choosing exposure. After doing all the obvious things to calibrate my exposure choice, I spin the iris and focus on the histogram. What I am looking for is a distribution of values that makes sense when I consider the scene in front of me and that spreads out the histogram. My goal is to get lots of discrete code values into the data set so there is more to play with in the grade. (Yes Virginia, that does require that you trust the colorist or are planning to do at least a primary "one light" grade yourself.) YMMV.

Cheers - #19

[Sascha Rossier]

Arnold. Thats why i mentioned NEAT VIDEO ;-) We all shoot underexposed from time to time (we don't always have a lighting-truck at hand, do we?) and push the ISO in post to get a reasonable exposure. Killing noise with a decent plug-in is all thats left to do ;-) The above theories is how you SOULD do it in a perfect world - But there is no perfect world (with lightingtrucks fittin into a backpack) and nobody forces you to stay @ 320 in post ;-)

[Jerrod Cordell]

It's hard to imagine that all the very dim, subtly lit shots I've seen made with the Epic and Scarlet were lit brightly enough to expose at 320 ISO. Take, for example, that one Jim posted in the Recon thread of Leonardo DiCaprio. I know I don't have the skills to throw 3K of light onto a scene (in order to keep it at 320) and make it look like it's lit by candle-light. In addition, I don't want to shoot wide open. I don't want the compromises in sharpness many lenses make wide open and I don't yet have the skills to work with the micro-thin of depth of field that results.

Actually that thing with Leo was shot at 2000 ISO if I remember right. Granted I believe they were using a fast Master Prime wide open but still the ISO was way up there if I remember right. And I don't believe they did any post processing on it either because they were specifically testing it for low light.

[Yousuf Abbasi]

What I don't understand about the "always shoot RED at ISO800 because it is native" is the following:

Let's say I shoot THE SAME scene using the two approaches below...

Case #1: Shoot at ISO320, and compensate exposure with a wider aperture (faster f-stop), while ensuring that RAW histograms are ETTR and highlights NOT clipped.

Case #2: Shoot at ISO800, compensate the exposure with slower f-stop, ensure that RAW histos are ETTR and highlights unclipped.

In Both cases, one could argue the image is "properly exposed" ... however, to me it seems that case #1 produces a better image because you have less noise due to the lower ISO!
(i.e. higher ISO brings more noise)

Therefore, if you know how to monitor your image and exposure properly, why wouldnt you prefer to shoot at ISO320 whenever possible ??