An open discussion of RED’s innovative ability to change ISO/ASA’s

[Lyndel Crosley SOC]

EFP/ENG Camera systems have never had the abilities of a DCS like RED to change the ISO/ASA. Most of us have digital still camera and we change the ASA/ISO all the time to suit our needs.
So my question is this:

Why is it that every article I read states that the DP shot the camera at 320 ISO?
Am I missing something here using this feature?
:head_explode:

 

[Derek Wiesehahn]

Think of it as if you were shooting film stock. The sensor has a sensitivity rating of between 250ASA and 320ASA. Changing the ASA setting in camera alters the metadata tag, but it does not alter the characteristics of the sensor, which is always capturing a RAW image. Any ASA above 320 will require a "push" in post, and any rating below 250 is a "pull" in post. If you take Kodak 320ASA filmstock, and shoot it with your light meter set to 800ASA, you will have footage which is "thinner" and noisier than it should be optimally. The same is true with shooting RED at higher ASA's.

 

[edmoore]

It wouldn't be a bad idea to affix a large sticker to the top of your monitor: "THE SENSOR IS ALWAYS ISO320! CHANGING THE SENSITIVITY IN THE MENUS DOESN'T ALTER THE CHARACTERISTICS OF THE SENSOR!"

That way you'd avoid the mistake I made where, missing an ND filter, I dialled down the 'sensitivity' to ISO100 and wondered why all my highlights were clipping halfway down the waveform monitor.

E

 

[Liam Hall]

EFP/ENG Camera systems have never had the abilities of a DCS like RED to change the ISO/ASA.

Yes they have. You can effectively change the ISO rating of most video cameras by altering the gamma set-up or by adding gain.

 

[Daniel Browning]

EFP/ENG Camera systems have never had the abilities of a DCS like RED to change the ISO/ASA. Most of us have digital still camera and we change the ASA/ISO all the time to suit our needs.

You have it backwards. Unlike ENG systems and digital still cameras, the RED ONE does *not* allow the analog
gain to be changed.

Why is it that every article I read states that the DP shot the camera at 320 ISO?

Because that rating results in a nice amount of highlight headroom and shadow noise.

EDIT: Here are a few more thoughts on the matter.

Gain vs. ISO

In many still cameras, the ISO setting is the exact same thing as the gain setting: it amplifies the brightness in-camera. Whether it is called ISO 800 or "+12 dB" is a separate matter.

Pre-compression gain vs. metadata gain.

ENG cameras and many digicams allow the option of increasing the gain of the signal (increase brightness) before it is compressed (recorded). Others, such as MFDB, digicams, and the RED ONE, offer metadata gain settings, which is just an "instruction" embedded in the file that indicates brightness should be increased in post production.

So whereas a two-stop gain on an ENG camera (+12 dB) will clip 2 stops of highlights, a two-stop gain on RED ONE (ISO * 2) will not change what's recorded at all.

The many definitions of ISO.

Every ISO rating is totally arbitrary. Some have 2.5 stops of highlight headroom, others 4. Most manufacturers aren't even consistent among their own product lines, let alone the difference between manufacturers. ENG cameras don't typically assign an ISO rating to their cameras.

Recommended ISO rating

RED recommends an ISO of 320 for the RED ONE. This results in a certain amount of highlight headroom and shadow noise. If you want more highlights and more noise, you can rate it higher. Lower ISO for less noise and less highlights.

Hope that helps.

 

[Lyndel Crosley SOC]

Daniel Browning < Thanks vary much for the extra information (i.e the Edit)


I do understand that the chip as an analog device is a constant. Also that the variance is in the Algorithm of the A/D processor as set by the values in the Algorithm as they affect lift, gamma and gain. I can see the point being the algorithm adjust for about 1 ½ stops in your high lights in its design.

My point I guess is that 320 ISO/ASA isn’t always the best for everything. If I may, I find in under lit areas (and that happens sometimes when you don’t have a full lighting package…laugh out loud) that 250 ISO/ASA is better giving me a stop on the low end.

 

[Brook Willard]

No matter what ASA you set the camera to, there will always be one "best" exposure. Choosing a different ASA to get there is just personal preference.

 

[Michael Brennan]

At the highlight end once the electron well is full it is saturated and white.
At the other end dark current noise and quantization noise from camera processing is the enemy.




Film needs 5-10 photrons to become developable, CMOS needs just a few.

CMOS and CCD sensitivity is fixed by laws of physics.
Regard each pixel as your light meter.

Like Brook said, there is only one correct exposure and 1/3 stop or more over/underexposure reduces the dynamic range that is going to cf card. Underexposure is less objectionable unless you have to lift large areas of shadow in post where noise will eventually become unacceptable.

In electronic cameras, dynamic range is expressed as SN ratio. Converting this science to film science of ASA, exposure latitude ect is not a perfect science.


Mike Brennan
ps
I think that NAC first invented the concept of changing gain, post shot in their slomo Memerycam back in ninties. The Memrecam was the first RAW recording camcorder and technically the first "progressive" camcorder although the term was not in use at the time Arri badge a NAC camera as the "Tornado"

 

[Lyndel Crosley SOC]

Hey Brook,
Nice work on ER hope the new show is going well.

As for best or optimal exposure we all know that a lens has a sweet spot. What that is can be subject to the math and the MTF curve. I think (and I could be wrong but) It would get pretty boring if everything was shot at a f/4. I would venture to say that ASA/ISO, exposure, Lens, DOF, COC, focal length are the variables in the formula that outline why the DP gets the big bucks. lol

 

[Brook Willard]

My point is that - for a given scene - there is an optimal exposure for the camera. The camera has a "window" of available dynamic range. Underexpose and you're not using the whole window... overexpose and you'll lose highlight data. There's always an exposure that will serve as the "best balance" in a particular situation. The "best" assessment is strictly from a technical perspective for the sake of this discussion... not creative.

Changing the ASA on the camera is merely enabling a different way of representing the same data. The decision to represent these data in a different way is a personal one - some people prefer to see the camera at 160 ASA to force themselves to give the camera enough light... some people prefer to see the camera at 320 ASA to get the most accurate representation of the exposure data in front of the lens. Regardless of your selected ASA, the "best" exposure at the lens will not change.

I never change the ASA from 320. I know how the camera performs with that curve in place and I know I can always get the optimal exposure in that mode. I do not think of the 320 mode as an actual 320 ASA sensitivity... but that's another story.

Ultimately, a cameraman can set the camera to whatever mode they personally prefer. Hell, some people set the camera to 640 ASA to earn the "texture" afforded by forced underexposure. That's another story as well.

So when I say "best" exposure, I'm not talking about the sweet spot of the lens. I'm talking about the point at which the camera is getting the best possible exposure from the light in front of the lens... not too much, not too little. If you change the camera to 160 ASA, that value does not increase a stop [just as changing it to 640 ASA would not decrease it a stop].

 

[Policar]

This is blatant fanboy stuff even by the poor standards set by this board.

ENG cameras have had gain since forever. The Red DOESN'T have gain and somehow that's an innovative feature that's never been offered? I now remember why I stopped reading this site.

 

[Brook Willard]

This is blatant fanboy stuff even by the poor standards set by this board.

ENG cameras have had gain since forever. The Red DOESN'T have gain and somehow that's an innovative feature that's never been offered? I now remember why I stopped reading this site.

Interestingly enough, only the initial post in this thread is championing the "innovative" ability to change ASA... and the other 10 posts are correcting it, pointing out that it is not innovative or new... and that it's just a different way of looking at the same data.

I understand your frustration - there is a lot of fanboyism on this site - but this is hardly the thread to make your point with. One must have a finely tuned bullshit detector on this - or any other - website. It is, after all, the internet.

But honestly, why make a post like yours? The purpose of this site is to educate and inform. If one had only read the RED ONE's marketing materials, they would think of the ASA adjustment as an innovative feature. Now those who feel that may stumble across this thread and learn how to more thoroughly understand the "ASA" functionality of the camera. It's something that you clearly already know, yes, but it's not something that everybody does. Is it their fault that you learned the details of the ASA adjustment before they did?

Don't think of it as fanboyism, just think of it as an incomplete understanding. If I only read the marketing materials for certain ENG cameras, I would be convinced that they were superior to film, infinitely sensitive and that I would never have to light a movie again. Further education would teach me how ridiculous those claims are. But would believing the hype make me a fanboy? Or would I just be partially informed?

Come on, please lose the attitude... this isn't the site for that. So next time - rather than reaming somebody out for being a fanboy - consider making your case and explaining the truth that you may have learned through experience. That's how people learn and that's what makes a forum a useful community. Then when they answer the same question for somebody else a few months down the road, they won't be tempted to roll their eyes and chew somebody out for knowing less than they do.

Carry on.

 

[Deanan]

If one had only read the RED ONE's marketing materials, they would think of the ASA adjustment as an innovative feature.

Really? Which marketing material did we say that in?

 

[Brook Willard]

Really? Which marketing material did we say that in?

Deanan, I didn't mean it like that. My point was regarding his rude and unnecessary comment - it was NOT about taking a shot at you guys in any way whatsoever. I phrased it that way to better illustrate my point that these forums are a great place to learn without the detractors.

But, just so I don't look like a jerk who makes this stuff up, this thread could give somebody the wrong idea about both the nature of and potential penalty for changing the camera's ASA. For example:

You get to decide your noise tolerance range and make ISO decisions based on that without worrying about color shifts or levels changes.

By that post, the only downside to choosing a different ASA is noise - not dynamic range, shadow or highlight information, etc. If that thread was a person's only source for knowledge of the camera's sensitivity adjustment, they could come to some conclusions that are not fully accurate.

That was what I meant in that one sentence in my post.

 

[Lyndel Crosley SOC]

Policar

I chose the words I did to spur a conversation on a topic. I’m well aware there’s a gain switch on most ENG camera and I also know a number of new camera’s in the film world you can change the ASA/ISO. I use them everyday.

My point was a conversation about the topic. I apologize to the Users group for this post and thank the members that have commented on this topic.

Lyndel Crosley SOC
Operator/Digital Image & Workflow Specialist
IATSE 600

 

[Brook Willard]

Don't worry, Policar has seen the err of his ways... he's cool.