Ahhh, the zebra stripes. You have seen them before. Some of you may have even shut them off. Others may be dimly aware of what they are for. But make no mistake; do not under estimate the value of the zebra stripes. This is your only real indication of lighting levels. NEVER TRUST A MONITOR. NOT EVEN THE VIEWFINDER. Trust the Zebras for accurate lighting levels.
When turned on it actually looks like Zebra stripes going across your viewfinder or flip-out LCD screen. They?re also called marching ants but let's stick with zebras. These lines are not recorded on the tape and they appear over any area that is overexposed over a certain level. Use this feature to guide the adjustment of the aperture and shutter speed to make your shot brighter or darker depending on what you?re shooting.
There are two basic types of zebra display, 100 IRE and another that?s often adjustable, 70-90 IRE. They are used differently, so it is essential to know which one you are looking at. Many pro cameras have both types, selectable in a setup menu. The first, 70-90 IRE, is primarily used for interview shots to properly expose facial skin tones.
70-90 IRE ZEBRA
The zebra pattern appears on highlights between 70 IRE and 90 IRE, and vanishes above 90 IRE. On some cameras the exact range is adjustable. Since properly exposed Caucasian skin highlights should fall at about 80 IRE, the camera operator adjusts the iris to display zebra pattern on the highlighted areas of the subject's face. Typically, zebra will appear on forehead, nose, and cheekbones. With a little practice, you become quite adept at setting exposure for faces with this tool.
Darker-skinned faces will display a smaller version of the same pattern; very light-skinned faces will display larger highlight zones. You simply need to mentally adjust for the type of face you are shooting.
100 IRE ZEBRA
The second type displays a zebra pattern only on areas of the picture which exceed 100 IRE, the upper limit of legal video.
With this type of zebra, the camera operator adusts the iris until the zebra is visible in highlight areas, then backs off until the pattern just vanishes, so you don't overexpose the scene. In the picture at left, the highlit areas of the snow-capped peaks are overexposed. If you overexpose too much in a digital format, you'll hit the 110 IRE ceiling and the whites will clip. You'll lose all detail in the clipped areas. This type of zebra pattern is more useful for general purpose exposure, but less accurate for setting closeups on faces.
Shooting The Thunderbirds or blue angels in the sky at those airshows and you?re getting 100 IRE from the sky- lower your levels to around 50% - i.e. these areas are highlights, but will not appear as white patches in the shot.
Look where the Zebra stripes are appearing. Zebra stripes all over the screen mean the shot will be too bright and details in the picture will be lost- its not even worth shooting.
Some cameras have a default setting at 70 or 80, while others are set at 100 IRE. For shooting on the fly, 70 or 80 are good luma values for facial tones. When you can't check the actual light values, zebras at 70 will generally be perfect for face shots. A camera that registers zebras at 100, on the other hand, will give you the correct value of white (100 IRE). Either of these zebras can give you a totally accurate evaluation of the light within the frame. If you aren't sure which IRE level your camera generates zebra bars at, consult the manual. Remember, if you get that wrong, your exposures will be off by several F Stops of aperture, either really really dark or really, really bright. Once again, you can't trust the monitor (not even the flip out), so use the zebras.
When keying or setting up a green screen you want even, consistent lighting with no dark spots. Instead of buying an expensive light meter, zebras can help you determine bad lighting and dark spots for a perfect exposure. Dark spots cause awful keys. If there is an area of shadow, it will appear as an area of broken zebras and your key is not a key anymore. Zebras at 100 IRE (the brightest) is a good setting to start at.
Last update: 07:23 PM Saturday, November 26, 2005