The Rules Of Log Exposure

WAVEFORM

TOOLS OF THE TRADE

Waveform. If you want to follow the rules of Log exposure, a good place to start is a waveform. The waveform is a scope that shows exposure in a brightness percentage from 0-100%. If you want to expose your middle gray correctly, pull out your gray card and adjust your exposure until it lands at the right percentage.

In the picture from the VariCam 35 (above), you see our gray card and matching waveform. The card on the waveform can be seen as a solid line, right at 42%. Nailed it.

FALSE COLOR

False Color. One of my favorite tools for exposing Log is False Color, which is a mode that overlays a specific color over a range of exposures. ARRI really made this feature popular with the ALEXA.

Notice that middle gray will be overlaid with a green color when it’s exposed correctly. Let’s break out our gray card again and adjust exposure until we see the card turn green.

The image at above (False Color) is from an ARRI AMIRA, but the VariCam 35 and HS use the same basic False Color system. You can see that our gray card has gone green, meaning we exposed it right. Nailed it.

ZEBRAS

Zebras. Another tool, which many of us use for exposure, is Zebras. This tool gets its name from the diagonal lines it overlays across your image. They can be set to different brightness percentages, and whenever a part of your image gets to that exposure, you’ll see those lines pop up. Most cameras actually don’t let you set Zebras as low as 40%, but the VariCam 35 can do that. Bringing out the gray card once again, I’ll adjust my exposure until the Zebra lines appear.

As you can see, the Zebra lines show up over our gray card just as expected (above). Nailed it again. I’m on a roll.

LIGHT METER

Light Meter. Okay, so up to now we’ve been using digital tools for Log exposure. But, for many of us, the best tool is a good old-fashioned light meter, and I’m excited to say that these meters work perfectly with Log exposure. The logarithmic gamma curves of these cameras are roughly linear with doublings, or stops, of light. This means that a doubling of our Log exposure is one-to-one with doubling of light, therefore, our light meters work!

That’s great news, but let’s test it out. Set your light meter’s ISO and frame rate to match the camera (say, 800 at 24p), break out the gray card, take a meter reading, and set your iris to what the meter reads out.

Having set my VariCam 35 to ISO 800 and adjusting the iris to match my meter reading, the middle gray exposure landed right where we wanted at 42%. Awesome. Your meter works, so feel free to use it all over set; put it right up in the face of your actors—they love that.

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