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Filed under: Cameras •Tips •Training •

Next Stop: The Last Stop! RED MX Latitude Tests

Here’s the test we shot with the camera rated at EI 800:

RED MX, EI 800, Camera RGB, RedGamma.

This is a cropped image from an Apple Color screen grab. I used Color for this test because I could interact directly with the R3D files. I opted to work in Camera RGB in order to see what was happening directly in the sensor’s color space. The camera was set to 5600k preset and I did no further white balancing. You can see the green hue from the spike in the LED illuminant. (The light source is a one-off prototype that will not ship with other Ambi-2 units until the spectrum has been perfected. The light is generally daylight-balanced but has some extra green in it. DSC is sending me a kit to convert this particular Ambi-2 into a tungsten-based unit for future tests.)

It’s important to know not to count that first wedge, the brightest one on the left. As the only solid reference point we have when evaluating a sensor is the point at which the photosites “saturate,” or clip, that first step is exposed so that it just barely clips. Starting with the next step down, the second wedge from the left, I can see 11 further steps and possibly part of a 12th.

It’s pretty hard to see this in RedGamma, so let’s take a look at RedLog instead:

RED MX, EI 800, Camera RGB, RedLog.

RedLog boosts the blacks up to about 20% on a waveform monitor, which makes it a bit easier to see how far down into the murk the wedges drop. Step 12 is directly above the “12” in “2012”, and there’s a very faint 13th wedge barely visible just to the right of that. And, deep in the noise, there’s another step just barely visible beyond that.

That seems to imply 12 stops of reliable latitude, which a couple of barely visible stops beyond that. Hmmm. That’s pretty impressive. Let’s take a look at what the objective data says:

RED MX, EI 800, Camera RGB, RedLog.

We’re looking at luminance only because the green channel tended to clip ahead of the others in RGB parade, due to the green spike in the illuminant. Remember, skip the first step as we’ve clipped that to set an objective starting point. Middle gray and black are much more difficult to define, and are often defined for us by the camera manufacturer based on how they think their camera looks the best. (The RED trusts us to do that on our own, according to our tastes and needs.)

Skipping that top step, I can see 12 steps total. The 13th is barely visible if you really look for it, as is the 14th step—but since they appear to have the same brightness level it’s hard to know whether to count them as they show up as the same tone, instead of separate distinct tones. The last step is just a scan line brighter than black, so I’m going to say that it’s probably too far down in the mud to be of real use. Based on this waveform I’d say that there are 11 solid stops of really useful latitude visible. If there’s detail in those steps it will be barely visible, and both steps will appear to be the same tone.

Just to double-check that, let’s look at the same image in RedGamma, which will push the shadows back down toward black the way we’re used to seeing them:

RED MX, EI 800, Camera RGB, RedGamma.

Now I’m only counting 10 stops. Stops 11 and 12 are visible as lines just above black, but they are of equal value so there won’t be much tonal difference between them using this gamma curve. Still, they’re down there if they are needed—although I suspect that you wouldn’t want to pull them up to make them more visible as they’d be awfully noisy so close to the noise floor.

Just for fun, let’s crank this thing up to EI 2000 and see how many steps we can detect:

RED MX, EI 2000, Camera RGB, RedLog.

RED MX, EI 2000, Camera RGB, RedLog.

The waveform shows us that the second wedge from the left is now effectively clipped, so we’ll ignore that one for now. If I look carefully at the image itself, above the waveform, I can see… wow, maybe 15 wedges from the left! Subtract the top two wedges and we’re down to 12 stops, which is consistent with what we saw earlier, at least visually. The thing that disturbs me about this image, though, is that steps 12 and 13 are very similar in tone, and steps 14 and 15 are basically the same very dark tone. If the steps don’t show up as separate tones, well… it’s hard to say whether they count. There will most likely be some detail in tones 12 and 13, along with a little bit of contrast, but it’s questionable how useful steps 14 and 15 will be in a real-world situation.

If we look only at the waveform, and start counting after the first two clipped wedges, I can see 10 distinct steps. The 11th is a tiny bump on the noise floor that slopes down into the remaining tones that we could see visually, but not terribly well. Keep in mind that this is RedLog again so the blacks are artificially boosted; if we look at RedGamma we’ll see something very different:

RED MX, EI 2000, Camera RGB, RedGamma.

RED MX, EI 2000, Camera RGB, RedGamma.

Starting at the third wedge from the left (the first one that’s not clipped) I see 10 solid steps in the waveform, for 10 solid stops. In the visible image I see another step for a total of 11 visible steps. The second wedge is clipped at EI 2000 but we know that it’s not really clipped at EI 800, so let’s add that back into the mix for 11 really solid stops that are detectable on a waveform monitor, and 12 that can be seen by eye.

I tend to be very conservative when it comes to exposure, dividing the dynamic range of a camera into “paycheck stops” and “gravy stops.” Paycheck stops are the zones upon which you can reliably place information that will definitely be reflected in a normally graded final image, and which won’t cost you your job when something that’s supposed to be visible there doesn’t show up in dailies. Gravy stops are the zones that will probably show up but that I don’t personally count on: if they are there, great; if not, but I don’t rely on them. Based on this model I see 11 paycheck stops and a further 3 gravy stops that aren’t visible on a waveform monitor but that are somewhat visible when viewing an actual image.

If I want something completely black I would expose my shadows below those last two gravy stops. Or I could very easily crush them in post as they are barely visible anyway.

The original RED ONE M sensor clocked in at around 9.5 stops of latitude, so 11 stops of solid latitude is a healthy improvement. The real treat is the increased speed of the camera. At low light levels contrast is relatively easy to control, as shadows seem to fill themselves in. There are many different explanations for this, including the theory that shooting wide open on a lens results in reduced contrast due to a certain amount of added lens flare, but the bottom line for me is that it’s more important to have a fast camera than to have one with 13 stops of latitude. (Although I wouldn’t turn one away…)

By looking at the images above it should be fairly simple for you to decide how you want to use this camera. Latitude isn’t just a technical choice, it’s an artistic choice—and artistic choices vary based on the person making the choices.

Disclosure: DSC Labs provided the charts used for this test at no charge.

Art Adams is a DP who lives in the shadows. His website is at www.artadams.net.

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Hey Art, very neat chart!

I wanted to point out that you can turn on the spot meter on the camera, which will bring up a small box on the EVF or LCD, and you can aim that box at anything you want and it will tell you the IRE value at the bottom of the screen. You can also use the joystick on the back of the RED to make the box bigger or smaller by spinning it clockwise or counter clockwise. I’ve found the spot meter to be very useful, but also more tedious than zebra’s, or the predator vision (which is questionable now in B.30).

Posted by .(JavaScript must be enabled to view this email address)  on  08/03  at  01:09 AM

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In just looking at the images and the waveforms provided I am seeing a tremendous amount of noise. I was wondering at what level of noise you wrote the image off as unusable? I have often found with the RED 5 or so stops of usable latitude and this has held true with my experiences with MX.

Posted by .(JavaScript must be enabled to view this email address)  on  10/14  at  10:23 PM

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