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Jarkko Virtanen

ISO value in RED

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Hi!

 

I have a friend who owns a RED and keeps saying that you can get more info to the over exposed part of the curve if you use ISO 500 instead of 320.

 

Do you have any facts or experience about this?

 

Thanks!

 

Jarkko.

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Hi!

 

I have a friend who owns a RED and keeps saying that you can get more info to the over exposed part of the curve if you use ISO 500 instead of 320.

 

Do you have any facts or experience about this?

 

Thanks!

 

 

Jarkko.

 

Hi,

 

Whilst that's true many others would suggest exposing to the right and using 160 ISO to reduce noise. It's a matter of testing & seeing what works for you in different situations. There is not one correct answer.

 

Best

 

Stephen

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I'd suggest using both: 500 for the bright areas, 160 in the dark areas. That way you account for it having less dynamic range than film. Even better, get comfortable with the false color and histogram displays. They tell you for sure when you run out of range. The Red is in many ways its own best light meter.

 

 

 

 

 

 

-- J.S.

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I'd suggest using both: 500 for the bright areas, 160 in the dark areas. That way you account for it having less dynamic range than film. Even better, get comfortable with the false color and histogram displays. They tell you for sure when you run out of range. The Red is in many ways its own best light meter.

 

-- J.S.

 

Hi John,

 

Very true, however when prepairing a light list I assume it's 160 ISO. That often has negative budget implications, prpbably the reason why I still shoot more 35mm than RED on low budgets commercials.

 

Best,

 

Stephen

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Ok thanks! I have to consider that.

 

But you are also saying that using ISO 160 instead of 320 reduces the noise? Well that might be the option for ND filters for me then... i'm just starting a production and there's going to be a lot of bright sunny days outside...

 

 

J.

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But you are also saying that using ISO 160 instead of 320 reduces the noise?

Yes. Basically, the Red's sensor has a fixed sensitivity which Red recommends rating at 320ASA (your own rating may vary depending on your tests). When you select an ASA/ISO value, it is just for monitoring. If you shoot at 500ASA, you are underexposing by 2/3 stop. Naturally then, you are also underexposing highlights by 2/3 stop and thus helping to protect them from clipping.

 

On the other hand, by rating at 160ASA, you are overexposing by 1 stop. The more exposure you give the sensor, the cleaner the image becomes. In my testing, going beyond 1 stop over made no difference. But since Build 17, I've found 320ASA to be very clean already, definitely good enough for greenscreen even under tungsten.

 

You have to balance these two variables on a scene to scene basis to get a clean image and also to protect your highlights. I would caution against overrating the camera in day exteriors where there is a lot of contrast unless you can live with a lot of clipped highlights. I also recommend using the in camera meters like the spot meter and histogram to judge exposure rather than going off the monitor.

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Ok thanks! I have to consider that.

 

But you are also saying that using ISO 160 instead of 320 reduces the noise? Well that might be the option for ND filters for me then... i'm just starting a production and there's going to be a lot of bright sunny days outside...

 

 

J.

 

Hi,

 

For bright sunny days 500 ISO is probably the way to go, however using more fill than you need on film would help conciderably with noise. With RED the sky often goes grey/white due to overload in bright conditions.

 

Stephen

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Hi,

 

With RED the sky often goes grey/white due to overload in bright conditions.

 

Stephen

 

Of course as with any format, this can be avoided with proper fill and filtration. I've also had good results rating at 250 and using MacGregor's look profile found on the other site hand in hand with false color.

Edited by Dominic Cochran

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Of course as with any format, this can be avoided with proper fill and filtration. I've also had good results rating at 250 and using MacGregor's look profile found on the other site hand in hand with false color.

 

Hi,

 

The crew of 'Knowing' would have done so if it was feasible. Sometimes accepting that the RED one has less DR than other more expensive cameras, would help people get the most out of it.

 

Shooting on film in such a situation can save the production time & money. Horses for courses.

 

Stephen

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No one will know till the cameras actually exist. But again, I'd bet on a 320 rating, though with more DR and a cleaner image to begin with so you could push/pull the chipset a bit more. A tradeoff comes as you cram in more megapixels you loose sensitivity (so i'm told) Hence the sensors might be "better," on scarlet/epic, but due to more pixel-elements on the chip, you're likely to loose sensitivity.

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160 ASA sounds a little conservative to me. I find exposing by eye tends to work pretty well at around 250 for interiors, in Rec. 709 (RedSpace lifts the mids a little more). And I'm very noise-intolerant and not as bothered by some about the way digital highlight clipping works, so I'm sure some people would consider even this too conservative.

 

Of course with the camera recording a linear raw file, there's no real penalty for putting middle gray in the "wrong" place, so there's no reason not to "expose to the right" as much as you can get away with without undesirable highlight clipping (which the camera provides about five different ways to check).

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I haven't been able to get my hands on RED, but I was wondering if the ISO is adjustable or are we just talking about using these ISO's for calculations?

 

Thanks,

Aaron

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I haven't been able to get my hands on RED, but I was wondering if the ISO is adjustable or are we just talking about using these ISO's for calculations?

 

Thanks,

Aaron

 

Hi Aaron,

 

With RED, ISO changes are metadata only. There is no effect whatsoever on the recorded image.

 

Stephen

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Guest TJ Williams

Its not quite clear to me that if the sensor has the sensitivity of 320 and one rates it as 160 noise will be reduced? I tried this and couldnt seeany diffeence in the noise????

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Its not quite clear to me that if the sensor has the sensitivity of 320 and one rates it as 160 noise will be reduced? I tried this and couldnt seeany diffeence in the noise????

By overrating the camera, you're overexposing the sensor. You get a better signal-to-noise ratio, and thus a cleaner image especially in the shadows. This works will all digital cameras, as well as with color negative filmstocks. It's subtle, so you won't see it on the HD-SDI out of the camera. You will definitely see it once in Redcine/Red Alert.

 

Here's some more technical reading on the subject: http://prolost.com/blog/2008/6/2/on-clipping-part-1.html.

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Its not quite clear to me that if the sensor has the sensitivity of 320 and one rates it as 160 ....

 

This is one of those strange subtle places where things start going in the wrong direction. Silicon chips don't *have* ISO sensitivities. ISO is defined in terms of film curves and densities and such. There's no definition of the term for any other imaging system.

 

So, in order to use our familiar light meters, we have to decide that these electronic things sorta work as if they were some ISO number or other. It's subjective, your opinion is as good as the next guy's. Test, look at it, take your pick.

 

But trust the camera's own histograms more than anything else.

 

 

 

 

-- J.S.

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Histogram and false color are the way to go. Expose to the right without clipping the whites and you should get the most out of the sensor. I always have my meters on set for red shoots but rarely bring them out anymore.

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This is one of those strange subtle places where things start going in the wrong direction. Silicon chips don't *have* ISO sensitivities. ISO is defined in terms of film curves and densities and such. There's no definition of the term for any other imaging system.

 

ISO definition is confusing for a digital camera and sometime a distinction is based upon ISO of a camera set and ISO relating to an image sensor. For camera ISO definition is recommended to be the one given by (4) below and for sensor it is advised to use the one given by (2) below.

 

The basic definition of ISO in digital imaging is:

 

(1) ISO = 10 / H,

 

where H some suitable chosen "adequate" exposure. For ISO 100 that would mean H = 0.1 lux-sec.

 

However, it is not always clear how to properly interpret the "adequate" exposure H and there are different ways to interpret it.

 

(2) Definition of ISO based upon saturation is based upon that exposure when image highlights are just below max possible saturation signal. H now is defined as 1/7.8 of the exposure at the saturation point. (7.8 = ratio of 141% reflectance to 18% gray.)

 

Therefore now,

 

ISO = 78/ Hs

 

(3) Definition of ISO based upon noise is when the exposure generates a "reasonably clear" picture at around 40 SNR.

 

(4) Definition of ISO when the exposure generates a picture of medium output level corresponding to 0.46 times the max output. 0.46 = (18%)^1/(2.2 sRGB gamma).

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Well, since Kodak switched from ISO to EI ratings, even film doesn't strictly use an ISO rating, the EI rating allows the manufacturer to fudge the rating one way or the other for optimal results. So digital and film are similar in the sense that there is a range that can be captured and you have a choice as to where to place your midtone values in order to optimize for grain, shadow detail, or highlights, etc.

 

One problem is that most of our thinking about exposing digital comes from the still photography world where we optimize an exposure shot by shot, not scene by scene as in a narrative production where consistency in signal strength for a whole scene's footage and thus noise level, blacks, etc. override notions that each shot has to be placed at the optimal exposure based on the amount of highlights and shadows in each set-up. Consistency & continuity from cut to cut in a sequence is something that still photography generally is less concerned with.

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The crew of 'Knowing' would have done so if it was feasible. Sometimes accepting that the RED one has less DR than other more expensive cameras, would help people get the most out of it.

 

I disagree. I think that film worked on every level, in part by either before or after photography making the story take place in fall, where cloudy, grey skies are the norm.

 

 

And, you can certainly blow the skies out with film. Especially on a bright, sunny day, it is very easy to have a huge differential between the exposure for the subject and that of the sky.

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I disagree. I think that film worked on every level, in part by either before or after photography making the story take place in fall, where cloudy, grey skies are the norm.

 

 

And, you can certainly blow the skies out with film. Especially on a bright, sunny day, it is very easy to have a huge differential between the exposure for the subject and that of the sky.

 

I love the romance of film... but some give it more credit than is real. Like it never blows out or blocks up.

 

Digital needs highlight protection. Film needs shadow protection. Ever have to deal with blocked up shadows? Ever miss exposure on film?

 

Try shooting any film at ISO/ASA 1000 and tell me how useable that is.

 

I have said before that I love film... but I also know from experience that it is not a cure-all, snake oil or a panacea. (Is that redundant?)

 

I know there are a lot of film fans here, including myself. Film is great, but there is a tendency to over- romanticize it? Just a bit? I'm not trying to say that digital doesn't have its own issues... but film is not perfect either.

 

The trick is learning the capabilities and limitations of whatever you are shooting...

 

This should kick off 100 posts... :-)

 

Jim

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I partly agree with you Jim.

There is a tendency for us to romanticise over film. But then we are artists and film has been our 'love-affair' palette for many many years.

 

To date I've shot nearly as much with digital, as I've shot with film.

 

but the one thing that irritates me about digital is that I feel that I need to be a technical engineer/scientist to work it.

I'm really not technically inclined, I'm more creatively based. The noughts and one's and how they work don't really interest me.

 

What interests me is how the light coupled with the camera move and the action taking place all marry with each other.

Not that if I change a matrix number from -1 to -9 that I'll have more give here and less there.

 

Even though there are some really beautiful digital images out there, digital hasn't found terra firme. Every day numerous posts surface, in various forums, that consistently highlight new issues which 'has-just-been-found' with latest digital cameras.

 

When I first started out I was given a great piece of advice.

Learn the technical side of things and make it 2nd nature, and once you do that, then you can concentrate on the artistic side of things.

 

Unfortunately with digital it just feels, in years to come, that most of us will be concentrating a bigger percentage on the engineering rather than the art. This I believe means that we could become more formatted...which I think our industry is showing signs of already.

 

When called upon, I'm hoping that your misterium x will bring an end to all the bullshit red posts and just allow us to go out there, shoot beautiful images with no nasty surprises.

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