Most prosumer cameras have a zebra strip function. Zebra stripes are a device that puts diagonal lines into highlights in the viewfinder that match a specific level (usually 90-100% of the maximum brightness) but it does not record the stripes on the tape or card. These stripes act as a indication of exposure levels to be used as an aid to getting the exposure that you want. You can think of a 100% zebra level as the equivalent of an audio meter that is telling you the sound is too loud (in this case the zebra stripes are indicating that the area is too bright.
A simple way to test this is to take your camera and point it up to the sky (on a fluffy cloudy day). Set your zebra stripes setting to 100%. Then set your exposure so that you get a few stripes on tops of the clouds. There should be a bright blue sky with brilliant white clouds that have depth to them. You will notice that the more you open up the iris the more the zebra stripes fill the clouds and you get a bright white sky with flat, white cloud. If you open the iris up even more you will eventually get a completely white sky with no clouds.
Some of the prosumer and the advance cameras will have several zebra settings that allows you to set the luminance level at which they become active. Usually videographers set the zebra stripes to 75% and that usually will give you a good exposure on the human face. You will see the highlights across the forehead or cheekbones. The downsize of setting your zebra to 75% is that there tends to be a lot of stripes showing up on your LCD screen and can be annoying to film like this. You can set your zebra to 90 or 95% to show the areas on the shot that are about to become over exposed so you can monitor those areas.
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| Picture from http://eyefish.tv/production-guide/technical-guides/exposure-and-zebra-patterns |
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