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Setting Exposure with Standard Gammas – Use your judgement!

First take a long look at the image to the left. look at the 3 small grey boxes. What do you see?
Is the middle of the three grey boxes brighter than the others? Does the bottom small grey box look about the same brightness as the top one?

This post comes as the result of a discussion going on elsewhere about how to correctly expose when using standard gammas. Basically discussing how to expose when your not going to do anything to your footage in post,  for what I would call “direct to air”.
There are many ways of setting exposure. You could use a light meter, you could use zebras,  you could use a waveform monitor or histogram.

Lets imagine that grey box is a face. If you were using zebras you would normally set them to between 65% and 70% and then expose the shot so the face exhibited the zebra pattern over any parts of the face not overly highlighted or in shadow. This is the textbook way to expose using zebras. Another way to expose might be to use a mid grey card (also known as an 18% grey card). With standard and cinegammas you would normally expose this at 50% using the cameras histogram, waveform monitor or spot meter. Again this is a textbook, technically correct exposure. But this is the real world and the real world is very different to the theoretical world because light plays tricks with our eyes and the overall brightness of a scene can change the mood of the shot.

Lets say you have a room with dark coloured walls.  At one end is a window and you have an actor standing at each end of the room, one against the dark wall, one against the window. We have two shots in our scene, one looking at the actor against the dark wall, one looking at the actor against the window. What happens if we expose both faces using zebras to exactly the same textbook 65% level? Well the face against the window will look darker than the face against the black wall. Look back at the grey boxes on the left. The top and middle grey boxes are exactly the same brightness but because the middle box is against black, to our eye’s it appears brighter than the top one. Now if we were to use a histogram or waveform monitor to expose these two shots, all the extra white in the window shot might tempt you to reduce the exposure, this would make the problem even worse. In fact to expose these two shots so that the faces match as you cut between them you need to reduce the exposure on the darker shot. Looking at the grey boxes again the lowest box is actually at 45% while the other two are at 65%, yet the lower box appears to be about as bright as the top box.
So what am I trying to say? Well exposure isn’t all about setting object “X” at exposure “Y”. You must use your judgement and a known monitor or viewfinder to asses your pictures. Learn to interpret what your monitor is telling you, learn to recognise scenes that may need to be exposed away from the text book values and methods. Above all else don’t be afraid to expose for what looks right, as opposed to object “X” at value “Y”.
I suppose to follow up on this I should tell you how to calibrate your viewfinder or monitor… I’ll do that soon in a later article. Did you find this useful? let me know, I’m planning on writing more about dealing with light and lighting.

Tags: exposure, light, lighting