The Rules Of Log Exposure

Lately, here at AbelCine, it seems like a new camera comes in every week. Technology is evolving very quickly, and we work hard to stay on top of it all, but for a working cinematographer, this can be quite a challenge. Recently, we received the new VariCam 35 and HS cameras from Panasonic and have been doing demos for many DPs. Of course, they all have different questions, but they consistently ask how to properly expose the camera. Like most of the digital cinema cameras today, the VariCam 35 and HS cameras have a Log recording mode, which Panasonic calls V-Log. Each camera, and its associated Log mode, is unique, much like a new film stock. So it’s not surprising that DPs would be asking us what the recommended exposure techniques are for the cameras. The good news is that the new VariCams work in much the same way as ARRI, Canon and Sony cameras that record in Log or RAW modes. This column is all about exposure techniques when working in V-Log, Canon Log, Sony Log (S-Log), LogC (from ARRI) and most RAW formats.

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Most of the camera manufacturers lay out some rules for exposing Log on their cameras. This means that they define how to expose for middle gray (18% reflectance) and white (90% reflectance) to maximize the dynamic range in your image. You can usually find these numbers buried in white papers filled with graphs and charts. Panasonic recently published one for the VariCam 35. Here are their exposure rules for V-Log (see the chart below).

They define where black, middle gray and white all fall in terms of both IRE % on a waveform and code values. As you can see, they say that their 18% gray reference should fall at 42% on a waveform, and a 90% white card falls at 61% on a waveform. It turns out that those numbers are pretty similar to other Log curves. Here they are compared (see the chart below).

TOP: Panasonic’s exposure rules for V-Log on their VariCam 35 to maximize dynamic range. ABOVE: The VariCam 35’s IRE % is similar to other cameras’ (ARRI, Canon and Sony) Log curves. Photos courtesy of AbelCine

From LogC to V-Log, most Log curves are about the same, which makes sense because they’re all designed to be similar to the original Log Cineon curve used by film scanners. This means that, for the most part, if we know how to expose Log on one camera, we can pretty much expose it on any of these cameras. And with all of the cameras noted above, exposing correctly for Log also means exposing correctly for RAW. That makes it pretty easy.

Now that we know the “rules,” let’s talk about how we can apply them with some exposure tools.