Question about RED ISO in available light scenarios

[Satsuki Murashige]

In terms of practical advice for the field, I would suggest acquiring faster lenses for these situations. Maybe a set of f/1.4 still photo primes like the Sigma Art series. And for day exteriors where you are shooting landscapes with bright skies, look into getting a set of ND grad filters and a polarizer in addition to your standard ND filters so that you can control relative exposure within the frame. If you are lighting an interview or faces, even a simple 5-in-1 fold up reflector or a 42"x42" beadboard (my go to) will help quite a bit. I usually carry a few collapsible 4x4 frames with a few diffusion rags for when there is no grip truck. Half Soft Frost diffusion can work wonders in harsh sunlight, and 4x4 is large enough for a medium close up.

 

[Terry VerHaar]

Hi Terry

I'm going to have to disagree. Changing ISO in-camera in the Red system is basically the same as printing up or down in the lab. It doesn't have any effect on your negative, unless you decide to under/over-expose further as a result. If your negative or .r3d is mis-exposed to begin with, changing ISO (or in this analogy, your printer lights) is not going to help. The best way to ensure you get consistent results is to test and figure out what combination of ISO range + light levels + OLPF gives you acceptable noise levels and then stick to those settings.

If you shoot interiors at 320 IS0 and day exteriors at 800 ISO (or even worse change ISO shot to shot within a scene) in order to 'optimize' the dynamic range of the sensor, then you are going to end up with shots that have inconsistent noise levels. If that is the look you are after, then all is good. But usually it just means your shots won't match and thus won't cut well. For that reason, I'll generally pick one ISO for a given 'look' and just light for that as I find it leads to more consistently exposed negatives. Now, if you're losing the light at the end of the day, then your choice is between underexposing and getting a noisy image versus having no image at all. But we should be honest that this is a necessary compromise, not the ideal.

Satski - I am not sure who you are disagreeing with but I don't think it is me. lol I guess I am just being inarticulate. Let's try again. RED has written a lot about this, both in the article I cited previously and in their excellent book The Rules of Engagement.

I think we agree that changing ISO doesn't change the dynamic range of the sensor. We also seem to agree that the only way ISO changes what you actually capture to your media is if you let it effect the way you expose the scene. As an aside, I rely pretty much completely on the histogram, goal posts and stop lights to get my exposure - trying to diligently avoid any reliance on the brightness of my monitor or the effect of ISO on the visual perception of the image. In the end, it really doesn't matter at what ISO you shoot since that is metadata. However, it does matter what ISO you end up choosing in post since that is where you have to deal with any noise or clipping that you may have encountered; kind of like your film print example. So, I think the argument for shooting at a particular ISO is to actually to get a visual hint of what your final image will look like; i.e.. whether you are actually protecting the highlights or reducing the noise in the visual representation of the image.

The difference in our representations is perhaps subtle but meaningful. I did refer to the change in "the negative" when referring to the change of ISO but I should have used the comparison of "the print" as you did. This is a better analogy. In fact, as you point out, the "negative" doesn't change but what we must be aware of is how we decide to "print" it.

Finally, the reason I think that understanding RED's approach to ISO is "counterintuitive" is because most cameras use electronic amplification or "gain" in the sensor, prior to exposure, in order to achieve higher ISO. This effectively makes the sensor "see more light" but at the expense of adding noise. RED's approach doesn't boost the signal but rather remaps middle gray. From the book...

"A higher ISO setting causes FLUT to remap dimmer objects to middle gray... this effectively shifts the number of stops that fall above and below middle gray, and compresses or expands the tones accordingly. At low ISO speeds, most of the dynamic range is below middle gray, whereas at high ISO speeds most of this dynamic range lies above middle gray." And later... "A key benefit of FLUT is that it remaps tomes without clipping the highlights or crushing shadows. All tones are retained-they are just redistributed."

Cheers. (And I hope this is a bit more articulate even though I doubt the entire subject can be given its due here.)

 

[Michael Tiemann]

I agree with the above except for one key typo. When you say "if you let it effect the way you expose the scene" you actually add to the confusion you are trying to clear up. If you had written "how you let it affect the way you expose the scene" it would be perfectly clear that it is how ISO affects a conscious process, not how it might (which it does not) effect a different behavior of the sensor.

 

[Terry VerHaar]

I agree with the above except for one key typo. When you say "if you let it effect the way you expose the scene" you actually add to the confusion you are trying to clear up. If you had written "how you let it affect the way you expose the scene" it would be perfectly clear that it is how ISO affects a conscious process, not how it might (which it does not) effect a different behavior of the sensor.

Thanks. Yes - that is what I meant, even if I didn't say it. LOL It is definitely about your perception of visual differences in viewing the image under differing ISO settings that might influence how you choose to set exposure and, in doing so, create problems. That's actually why I rarely shoot at any setting other than 800 and diligently monitor the stop lights, histogram, goal posts and, more recently, the GioScope.

 

[Satsuki Murashige]

Satski - I am not sure who you are disagreeing with but I don't think it is me. lol I guess I am just being inarticulate. Let's try again. RED has written a lot about this, both in the article I cited previously and in their excellent book The Rules of Engagement.

I think we agree that changing ISO doesn't change the dynamic range of the sensor. We also seem to agree that the only way ISO changes what you actually capture to your media is if you let it effect the way you expose the scene. As an aside, I rely pretty much completely on the histogram, goal posts and stop lights to get my exposure - trying to diligently avoid any reliance on the brightness of my monitor or the effect of ISO on the visual perception of the image. In the end, it really doesn't matter at what ISO you shoot since that is metadata. However, it does matter what ISO you end up choosing in post since that is where you have to deal with any noise or clipping that you may have encountered; kind of like your film print example. So, I think the argument for shooting at a particular ISO is to actually to get a visual hint of what your final image will look like; i.e.. whether you are actually protecting the highlights or reducing the noise in the visual representation of the image.

The difference in our representations is perhaps subtle but meaningful. I did refer to the change in "the negative" when referring to the change of ISO but I should have used the comparison of "the print" as you did. This is a better analogy. In fact, as you point out, the "negative" doesn't change but what we must be aware of is how we decide to "print" it.

Finally, the reason I think that understanding RED's approach to ISO is "counterintuitive" is because most cameras use electronic amplification or "gain" in the sensor, prior to exposure, in order to achieve higher ISO. This effectively makes the sensor "see more light" but at the expense of adding noise. RED's approach doesn't boost the signal but rather remaps middle gray. From the book...

"A higher ISO setting causes FLUT to remap dimmer objects to middle gray... this effectively shifts the number of stops that fall above and below middle gray, and compresses or expands the tones accordingly. At low ISO speeds, most of the dynamic range is below middle gray, whereas at high ISO speeds most of this dynamic range lies above middle gray." And later... "A key benefit of FLUT is that it remaps tomes without clipping the highlights or crushing shadows. All tones are retained-they are just redistributed."

Cheers. (And I hope this is a bit more articulate even though I doubt the entire subject can be given its due here.)

Yes, I agree with you here. My point of contention was the idea that using ISO to freely allocate stops above and below middle grey as a general exposure strategy ignored the byproduct of inconsistent noise levels shot-to-shot, which in my view is worse trade off than losing a stop in the highlights, since that can usually be compensated for with filtration, grip, or lighting. If you didn't mean it that way, then I apologize.

 

[Terry VerHaar]

Yes, I agree with you here. My point of contention was the idea that using ISO to freely allocate stops above and below middle grey as a general exposure strategy ignored the byproduct of inconsistent noise levels shot-to-shot, which in my view is worse trade off than losing a stop in the highlights, since that can usually be compensated for with filtration, grip, or lighting. If you didn't mean it that way, then I apologize.

Totally agree. In everyday practice, I tend to set one ISO and forget it. In fact, I only see mucking with ISO as a bit of a "desperation move" if you are going to be shooting in consistently unfavorable lighting conditions that can't otherwise be mitigated.

 

[Sabovic Adis]

I get it. Colorists might default the footage to 800iso red long film and not know you rated at 1600, but I know what you mean. I think when using the ISO in the way described in this thread I would be more apt to call it digital gain. The best thing you can do in low light scenes like the ones describes is use anything, even a couple of LED torches to pop some pocket lighting into the scene and if you can, use available to the max advantage.

David

Yes. :biggrin:
One more thing good to know, as I see it, is that You already are "developing" as soon as You're seeing any picture coming from RED cameras, be it on set or in post. ISO means "post - sensor" and "post - recording". "Pre - sensor" is only that wich really is pre - sensor: lens (its aperture), filters etc., and these are the only means that can be used to "properly expose" the sensor to light.
The only "problem" is that we don't know the "proper sensitivity" so we never can tell if we're actually overexposing, underexposing or just nailing it. But, I guess, that's just...ugh...academical. :lol: