ISO / ASA Explanation
ISO / ASA
Although there are many opinions on this and it is one of the most misunderstood topics with regard to the operation of the RED one we at Red one rentals have through a huge amount of testing and studying been able to thoroughly demistify this subject. After all this time though the basic fact is that there is nothing really that complicated going and that in most situations merely exposing at the Sensor's native sensitivity of 200 to 320 is the best practice. We understand how this works and have no uncertainties when it comes to proper exposure.
The following is pulled from REDUSER.net: and we have found it useful along with a multitude of other discussions on the subject that live there.
Ultimately, the camera's native ASA for a given scene comes down to two things: the contrast range of the scene and your willingness to accept overexposure.
If you look at exposure from a strictly technical perspective, your goal would be to capture as much detail as possible. Accordingly, you would want to overexpose as much as possible without clipping data. This would bring the most exposure into the shadows as possible and give you the [excuse the term] "thickest negative" possible.
So if you're in a scene with barely a stop or two of dynamic range, you may find that the "technically perfect" exposure may put your ASA closer to 200. If there's nothing hot enough to clip you early, you can open up significantly more than you otherwise would be able to.
Consider the alternate situation: a contrasty day exterior with the sun in frame. The sun is going to clip - that's a given. But how much of the sky are you willing to lose? Do you want to see every white cloud up there? Well you're going to need to stop down significantly in order to see it... pushing your relative ASA into the 640+ range easily. The "technically" best exposure will always vary depending on the subject.
Now, forgetting about the technical, approach exposure from an artistic angle. It's a night exterior and you want most of the frame to be black. You rate the camera at 320, pick a healthy stop and look at the monitor. Great! It's dark, it's contrast and it feels like night.
If you looked at that same scene from the technical perspective, the histogram might scare the shit out of you. It'll be so far to the left that what you see really is all you'll ever get. While the best "technical" approach may be to open up more [lowering the rated sensitivity] and bring more light into the shadows, that'll make an overexposed-looking night image. Sure you could crush it in post and have a noise-free dark image like you intended... but nobody wants to hear about that on set.
You probably already know all of this - if so, the post is for the benefit of those that don't. Ultimately, exposing for the RED should be handled by looking at the monitor and histogram instead of at a light meter. If the meter says it's a 2.8 but it looks more properly exposed at a 2.0... put it at a 2.0. If the meter says it's a 2.8 but the camera says it's clipping... put it at a 4.0! So how do you rate the sensitivity of something whose proper exposure varies so much depending on the nature of the scene?
I dunno.
Like David said, test the bejeezus out of it. But - in my opinion - you should be lighting to 320... and stopping down if the situation calls for it.
But I'm personally willing to add special sauce in post. I also like the cleanest image possible.
I'll go to 500ASA if I don't have enough light for 320 [or, conversely, if I have too much light to prevent clipping], but I'll always grab the iris and fine-tune the exposure regardless of what the meter says.
I'll generally put the camera at 500ASA when I'm outdoors... just to idiot-proof it for the DP. I'll explain what I'm doing and why, but that extra 2/3 stop buffer is great for saving an "oh, crap" moment.
Although there are many opinions on this and it is one of the most misunderstood topics with regard to the operation of the RED one we at Red one rentals have through a huge amount of testing and studying been able to thoroughly demistify this subject. After all this time though the basic fact is that there is nothing really that complicated going and that in most situations merely exposing at the Sensor's native sensitivity of 200 to 320 is the best practice. We understand how this works and have no uncertainties when it comes to proper exposure.
The following is pulled from REDUSER.net: and we have found it useful along with a multitude of other discussions on the subject that live there.
Ultimately, the camera's native ASA for a given scene comes down to two things: the contrast range of the scene and your willingness to accept overexposure.
If you look at exposure from a strictly technical perspective, your goal would be to capture as much detail as possible. Accordingly, you would want to overexpose as much as possible without clipping data. This would bring the most exposure into the shadows as possible and give you the [excuse the term] "thickest negative" possible.
So if you're in a scene with barely a stop or two of dynamic range, you may find that the "technically perfect" exposure may put your ASA closer to 200. If there's nothing hot enough to clip you early, you can open up significantly more than you otherwise would be able to.
Consider the alternate situation: a contrasty day exterior with the sun in frame. The sun is going to clip - that's a given. But how much of the sky are you willing to lose? Do you want to see every white cloud up there? Well you're going to need to stop down significantly in order to see it... pushing your relative ASA into the 640+ range easily. The "technically" best exposure will always vary depending on the subject.
Now, forgetting about the technical, approach exposure from an artistic angle. It's a night exterior and you want most of the frame to be black. You rate the camera at 320, pick a healthy stop and look at the monitor. Great! It's dark, it's contrast and it feels like night.
If you looked at that same scene from the technical perspective, the histogram might scare the shit out of you. It'll be so far to the left that what you see really is all you'll ever get. While the best "technical" approach may be to open up more [lowering the rated sensitivity] and bring more light into the shadows, that'll make an overexposed-looking night image. Sure you could crush it in post and have a noise-free dark image like you intended... but nobody wants to hear about that on set.
You probably already know all of this - if so, the post is for the benefit of those that don't. Ultimately, exposing for the RED should be handled by looking at the monitor and histogram instead of at a light meter. If the meter says it's a 2.8 but it looks more properly exposed at a 2.0... put it at a 2.0. If the meter says it's a 2.8 but the camera says it's clipping... put it at a 4.0! So how do you rate the sensitivity of something whose proper exposure varies so much depending on the nature of the scene?
I dunno.
Like David said, test the bejeezus out of it. But - in my opinion - you should be lighting to 320... and stopping down if the situation calls for it.
But I'm personally willing to add special sauce in post. I also like the cleanest image possible.
I'll go to 500ASA if I don't have enough light for 320 [or, conversely, if I have too much light to prevent clipping], but I'll always grab the iris and fine-tune the exposure regardless of what the meter says.
I'll generally put the camera at 500ASA when I'm outdoors... just to idiot-proof it for the DP. I'll explain what I'm doing and why, but that extra 2/3 stop buffer is great for saving an "oh, crap" moment.
