Using a light meter on a polar bear & curtain

R

rc444

Well-known member
Were I to use a light meter on a polar bear, (assuming that the polar bear is stark white), logic would dictate that the bear would come out grey if shot that way. This is because the light meter by default measures light at 18% grey.

My question is... how many stops compensation would I need to make in order to replicate the true white colour of the polar bear???

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I also have another quick question. Were I to meter a completely black curtain, logic would dictate that if I took a reading, the curtain would come out grey also. (Correct me if I'm wrong).

How many stops compensation would I need to make in order to replicate the true black colour of the curtain???

Thanks guys,
rc444
 
On a video camera? You can't. Stop trying. A lightmeter is only a vague reference for use with a video camera.

The only way you could do what you're talking about is if you used a specific lightmeter like the newest Sekonic that lets you "profile" the meter for your sensor, and then furthermore if you only used the settings that you specifically calibrated the monitor to. If you change your gamma, your presets go out the window. And if you're exposing at the most-open end of the lens, your readings go right out the window.

Use zebras instead. Use a waveform monitor. Use tools designed to work for video.
 
rc444's logic only applies to a reflective meter. To solve the problem, do 1 of 2 things:
1. Point the meter at a grey card under the lights of the set, or
2. Use an incident meter (the kind with the white half-ball on it).
But this is only for mediums where you can set the accurate film speed (ASA, ISO) of your pick-up medium (like film - not like video, as Barry noted).
 
Both questions require the knowledge of how much latitude your capture medium has. Are you shooting reversal, the new vision3 stocks, video?

You should know beforehand what the medium is capable of and use the 18% as a reference to determine how many stops over will be white, and how many stops under will be black.

With Kodak, you can consult data from their website, and tweek the numbers in transfer or IP printing.

With video, I'd use a waveform either on set or with tests beforehand.
 
In this situation it is important to understand the difference between reflective and incident metering. What rc444 is referring to is obviously in a spot metering mode, or a reflective reading. When a reading is taken in incident, it measures the amount of light falling on the subject, and calculates that into an f/stop.

j is exactly right in saying that in order to work out this problem, you must first calculate the amount of latitude your working with, and from that point, use the Zone System or other scale system to determine at what point above or below 18% grey, pure white or black will land.

Happy shooting!
 
When metering Polar Bears, the instrument of choice is always a spot meter. Same with crocodiles.
 
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