Native ISO Rating

[Zhibo Lai]

Sometimes it's easier for me to understand if I've put it in my own words. Can you tell me if the following statement is true?:

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.

I would add this to it (this is based on my 2 weeks Scarlet shooting experience and combing thru endless threads on RAW vs ISO, and coming from a HDSLR past-life):
The MX sensor, like all current digital camera sensors has only one sensitivity. When you boost the gain in HVX or iso in a 5D, you are not changing the sensitivity, you are digitally boosting the iso and baking that into your clip. With Red cameras, you also have this same option of digitally boosting the iso, except Red does not bake that into your clip. Red gives you the RAW sensor data so you can change iso in post to your liking. The other cams do not offer this feature.

Changing iso on Red gives you an idea of what the image will look like at that exposure. A good rule of thumb is to stay within the goal posts. Those are always RAW, regardless of what iso you select, they don't change. If you don't clip RAW, you have more room in post to adjust the image.

In addition to shooting 800 iso for highlight protection, I'll change up the iso and monitor the histograms for how much "acceptable" clipping there is. This will give me an idea of how much latitude I have to adjust the iso in post.

 

[Jon Thomasberg]

SHOOT 320.. ALWAYS.. 800 is just mental masturbation..

I like the analogy!! Makes you feel better but doesn't change anything in the grand scheme of things.

Check your goal posts.. Check your exposure mode. If its too purple, open up or add light.. If its too red, close down, ND.

Agreed...

If you are still crushing blacks and clipping your highs and have exposed correctly, get a new DOP / Gaffer that can properly light a scene within the latitude of the camera. If that DOP/Gaffer is you, and you have budget -- hire a competent one; if no budget -- learn how really quickly.

 

[Wey Wang]

Thanks for the great discussion guys! Lots of knowledge and it really helps clarify things.

 

[Matt Ryan]

Think of a settings change in camera as a viewing LUT on your monitor and that may help you understand.

The idea behind shooting with ISO 800 is one, protecting the highlights, and two, the ability to have a noiseless image in lowlight at 800 ISO. It is agreed amongst a majority that shooting at 800 gives you the best tradeoff between the highs and lows in your exposure.

Keep in mind that the camera has 13 stops of DR, so make sure to expose accordingly to utilize all those stops. Basically dont crush something if you want to bring it up in post and dont blow something out if you want to bring back detail in post.

As long as you are exposing by the histogram and false color your set regardless of what ISO you choose. No one will ever agree on one ISO so use what works best for you and gives you the results you want.

 

[Arnold F.]

Not much help if you don't know what a LUT or crushing is!

Another thing I'm still not clear about is the apparent conflict between the opinion that you should shoot at either 320 or 800, but that you can shoot at any ISO if your indicators are okay. If I'm not adding gain/grain, why not shoot at 3200 all the time and just watch my indicators?

Think of a settings change in camera as a viewing LUT on your monitor and that may help you understand.

The idea behind shooting with ISO 800 is one, protecting the highlights, and two, the ability to have a noiseless image in lowlight at 800 ISO. It is agreed amongst a majority that shooting at 800 gives you the best tradeoff between the highs and lows in your exposure.

Keep in mind that the camera has 13 stops of DR, so make sure to expose accordingly to utilize all those stops. Basically dont crush something if you want to bring it up in post and dont blow something out if you want to bring back detail in post.

As long as you are exposing by the histogram and false color your set regardless of what ISO you choose. No one will ever agree on one ISO so use what works best for you and gives you the results you want.

 

[Jake Wilganowski]

Because that would be very inefficient , you would have a huge gap between what your monitor is seeing and what your recording

 

[Matt Ryan]

Not much help if you don't know what a LUT or crushing is!

Another thing I'm still not clear about is the apparent conflict between the opinion that you should shoot at either 320 or 800, but that you can shoot at any ISO if your indicators are okay. If I'm not adding gain/grain, why not shoot at 3200 all the time and just watch my indicators?

haha a LUT is basically a "Look" applied to the original captured image for viewing and not what is actually registered.

You could shoot at 3200 if you'd like, but what that means is when you expose for your highlights you will crush your mids/lows. If you were to look at your histogram in daylight and only increase the ISO, you will notice your histogram moves further and further to the left (underexposed side) as you expose for the highlights and increase the ISO. This will cause "crushing" (underexposure) that wont be recovered. You will thus eliminate all those stops of Dynamic Range that you've been given with the camera.

800ISO is the best "tradeoff" for daytime and low light settings.

The thing about exposing is you want the fattest (most equally spread histogram) you can possibly get.

Whatever ISO you choose you want a fat (evenly distributed) histogram, and seperation between your lows, mids, and high's for the best image possible. Obviously, dont underexpose the low end, or overexpose the high's as well.

 

[Arnold F.]

And if I open up to compensate for the ISO change then the histogram will move back right, will it not? I honestly don't have enough lights to light for 320 at night. All of these subtle shots I've seen, like the one with Leonardo (cringe) smoking, are lit bright enough to have a balanced histogram at 320? I'm not an expert but there's no way that has a spread out histogram at 320 or even 1600. It's near complete darkness.

 

[Matt Ryan]

Leo was shot at 2000ISO and if you could see the histogram I guarantee everything was bunched on the left as well as crushed areas. If in lowlight and you expose for 320 your histogram is going to be more to the left than at 800. If you bring in more lights to light the scene at 320 ISO your histogram will move back toward the right. But if you expose correctly at 320 you will have more room to bring the image up in post without noise than at 800.

Night is another subject. Your going to get underexposed areas if you don't have the light. People get into trouble when they assume they can bring it up in post which is why you see soo many noisy video's. Once you have underexposed something, it's gone. You have to make sure you keep it that way in post and resist the urge to bring it up.

I was lucky enough to have an ASC/AIC Cinematographer as an instrutor in film school. His lesson on lighting was "imagine a pitch black room, and now tell me what you want to see. If you want to see something you light it, if not, let it go." It sounds simple but it helps a lot when your in low light situations to take a second and imagine it that way. Painting with light. Same goes with exposure.

 

[Mike Lary]

Sometimes it's easier for me to understand if I've put it in my own words. Can you tell me if the following statement is true?:

The sensor has one sensitivity, 320 ISO, and all others can be thought of as "virtual" ISO's.

Not true, but half correct (the first part). 320 is also "virtual" in that it has no direct correlation to the raw data - it's an interpretation. Comparing the ISO histograms with Raw to see which is closer (or the same) is bunk. Additionally, all the colorimetry is geared for 800. Getting the best quality image isn't just about sensitivity. It's better not to think of a specific ISO for the sensor and instead consider the sweet spot to be somewhere between 320 and 800 depending on your shooting conditions. Taking an "always shoot 320" or "always shoot 800" approach is limiting and in the case of the former it's risky.

 

[Jake Wilganowski]

So much grey with red : )

 

[Noah Yuan-Vogel]

If I'm not adding gain/grain, why not shoot at 3200 all the time and just watch my indicators?

Because for most shooting environments, if you are exposing using your traffic light indicators to expose to the right, shooting at ISO3200 will look wayyy too bright.

All of these subtle shots I've seen, like the one with Leonardo (cringe) smoking, are lit bright enough to have a balanced histogram at 320? I'm not an expert but there's no way that has a spread out histogram at 320 or even 1600. It's near complete darkness.

That shot was done at ISO2000, and probably if they had monitored at a lower ISO and set exposure for that, it wouldn't have held his face so well when illuminated brightly by the match.

One of the beauties of RED is that you can tweak looks in camera quite effectively with a user curve so if ISO2000 or ISO3200 looks too noisy in the low end for you in your tests you can always tweak to crush or reduce contrast in shadows to minimize the appearance of noise to your liking.

 

[Les Dittert]

Compare real world ISO's:

Shoot picture with Red and Canon lens. f8 at 1/100 ISO 800
Shoot same pic with same lens at same settings on Canon DSLR.
Develop both with your favorite RAW process.
Compare noise.
That is how you see how things match up with reality. It's all about noise at a given ISO.

 

[Matt Ryan]

320 is more valid when it comes to the Red One M sensor. New sensor, new rating, new technology. MX has more latitude than the previous M sensor so it's rated accordingly at 800ISO. Think of the M and MX sensor as film stocks. The M was rated at 320 and 11 stops of DR, the MX is rated at 800 and 13 stops of DR.

However you choose to use ISO, expose accordingly.

 

[Wey Wang]

My background is with film and DSLR shooting. I'm trying to treat the camera as a single filmstock rated at a particular ISO. With that in mind, my goal is to expose in the middle, 6.5 stops over 18% grey and 6.5 stops below 18% grey. All while not clipping the highlights and trying not to introduce noise in the shadows.

It's just a little disconcerting to have the RAW histogram match up at ISO 320 and then be recommended to meter at ISO 800. It's kind of hard to know what lights to order if you don't know what your filmstock is. And the difference between ISO 320 and ISO 800 is a good stop difference.

My concern, is if I meter and shoot at ISO 800, but the raw is really seeing less at ISO 320, and I'm already protecting highlights, I'll be continually underexposing.

 

[Matt Ryan]

The thing about RAW view is it's a holdover from the original M Sensor. It was calibrated and set for that specific sensor back in 2007. Now with the MX sensor RED recommends 800ISO (more sensitive sensor). I'd say do a test yourself: Shoot a greyscale and expose for 18% at both 800ISO and again at 320ISO. 800 will be a better overall rating in the amount of latitude you get on both sides (Over and Under). 800 is just the best "tradeoff" between lighting situations and proper exposure.

Almost every DP will rate a camera differently just like most DP's rate a stock a bit differently. It's going to be different for every person depending on the look/style they are going for and the conditions they are shooting in. The advantage to RAW is it's all just metadata and it's all adjustable if you expose correctly to begin with.

 

[Wey Wang]

Thanks, Matt. That makes a lot of sense. Here's hoping they update the "Check RAW" to reflect the new sensor.