Zebra Basics

[Chris Long]

Hi All
Funny that I come to this issue so late in the game, but it's just one of those things that I've successfully ignored until now. Now that I've gotten better at other things, I can turn my attention to the zebra functions on the PDX-10.

Frankly, I'm pretty ignorant about the zebra pattern. Why, and most importantly, how should I use it in practical application? I understand its purpose (safeguarding from over-exposure; an aid to correct exposure) but not how to apply it.

When set on 70%, I seem to see more zebra stripes than when it's on 100%--why is that? What does that mean? Do some of you leave it on at all times? Which setting is preferable?

I guess I want to know how those of you who regularly use the feature apply it to their work.

Thanks--sorry for such a basic question, but my search of the forum left me with more answers than certainties.

Chris

[Greg Boston]

Chris,

There are other threads that have discussed this but in short, you are correct. The zebra bars are telling you that areas of the image are overexposing. To me, I use them as quasi contrast meters. The zebra bars sometimes show up in parts of the scene other than my main subject. This tells me the scene has too much contrast and that I need to somehow reduce that using a different camera angle, adding lights, etc. Digital video is very intolerant of blown out highlights. You can sometimes push the levels up in your editor to brighten dark areas, but you can never recover information in blown out highlights.

On my original XL-1 and the Pana 953, the zebras are fixed at 100 IRE. As you have noted, yours are adjustable. This is to allow you more of a safety margin if you set them below 100. That's why you see more zebra at 70 than you will at 100. You are telling the camera what you want as a 'do not exceed' value for brightness in your scene.

Hope this helps.

=gb=

[Wayne Orr]

Let me approach the idea of contrast control from a different angle.

Let's say a normal picture has a range of zero to one hundred. Anything that gets down near zero is black, and anything that exceeds one hundred is "clipped", that is, loses detail.

Additionally, when we look at flesh tones on a normal caucasion face, we see that a nicely exposed skin tone falls around 65%. More on this later.

Now all this is pretty much a guide. Some dark items will lose detail, or be crushed before other objects in the same shadow area. We learn to note these details on our monitor, or better still, with our trained eye before we even turn on the camera. Same goes with "highlight" areas. We learn not to position our subject in front of the bright window because the sunlit scene outside is way too bright versus where the subject is seated.

OTOH, it is not impossible to shoot the subject in front of the bright window, but you must know that what is in the shot outside will be "burned out." Sometimes, especially shooting documentary, you must "shoot 'em where you find 'em," and you accept the burn outs.

OK, so we can use the 100% zebras to warn us that we are about to lose detail in the scene. (In truth, we can actually go to about 107 before the camera's built in circuitry will clip the image) So we can adjust our picture till we see just a bit of 100% zebras in the brightest portion of our picture. This might be the sky, or it could be a table lamp shade.

But while this might keep us from overexposing a portion of the frame, it doesn't help us with properly exposing a human being in the shot, and may very well underexpose the human being.

Enter the 70% zebras. If you adjust the 70% zebras till you see a bit of them in highlight areas of the face, such as the forehead, the bridge of the nose, a cheek bone, then you can be reasonably certain the overall face is falling somewhere in that desireable 65% zone that we noted earlier. This is why I prefer using 70% zebras as a guide, versus 100%. You should be able to use your eye to note where you will have possible overexposure problems in your frame, and the 70% zebras will guide you to the best setting for what is probably the most important area of your frame, the real people.

After you set your exposure on the humans, you can switch to 100% and see if there is anything you didn't notice by eye, for instance a light that is too hot, and maybe just needs to be turned down a click or two.

News shooters have a bad habit of using 100% zebras too much, because they have been bitched at by the techies at the station to avoid overexposure. So they come back with faces underexposed, but the sky looks great. Please, I am not talking about most news shooters, usually the newbies.

A couple other notes about using 70% zebras. You want to see the zebras in the highlight areas of the face, such as the bridge of the nose, forehead, cheekbones. Use the zebras according to the lighting source. For example, if you are under fluorescent overhead lights, you want a bit of zebras on the bridge of the nose. But if you are outside in the bright sun, you might take a bit more of zebras because of the bright lighting conditions. If you are shooting an interview, with a strong side light source, take a bit more zebras than if the source is head-on, to indicate the source. (The use of a practical light in the background on the key side will help sell the effect)

One of the great things about using the 70% zebras, is if you underestimate the exposure using the zebras, you will almost certainly be in good shape, since this camera (as with most video cameras) still looks good underexposed a bit. But it sucks if you overexpose.

Another good point about 70% zebras, is if you want to match your lighting when shooting a "film" (for reverses, for example) you can give your actors equal zebras, and you will be in pretty good shape.

One final word of advice, and this is the dirty little secret. You will get different exposure settings if you look for zebras from iris opening versus iris closing. I strongly urge you to set your zebras by starting from a closed (or close to it) setting. For example, with your camera pointing at your subject, be certain to close your iris (or close to it) before looking for the zebra. Now, begin opening the iris slowly, until you see the zebras on the highlight area. Let me put this another way: set your iris at F11 (or close to it) and begin opening your iris toward f/1.8, stopping when you see the zebras.

Enjoy. And don't expect it to simply fall into place. It takes practice and skill to make pretty pictures.

Wayne Orr, SOC

[Chris Long]

This explains quite a bit--thanks, Greg and Wayne. I need to go out and paly with it some more.

Thanks for the help--
Chris