Film Lighting
Page 12
John Alonzo, ASC
The prettiest use of any color film is when you have a sort of step-by-step scale of color value, of light and dark, so if your entire frame has 30 percent black and 30 percent white, then you want to take the other 40 percent somewhere between these two ratios of bright and dark. It is a matter of taste, but it does give you the best reproduction for color. Step all the values in the frame with your eye. Say that 20 percent of it is white hot sky and the rest is various gray values till you get to black.
In low-key lighting the frame will be predominantly dark, whereas in high-key it is predominantly light. The brightness range of a scene can be measured in several ways. A spot meter will give absolute values for various small areas in the frame. The contrast viewing glass gives an overall impression of how the film will interpret the brightness range, as does a still photo of the scene. The experienced cinematographer, however, comes to be able to judge the range by eye. We must understand that the brightness range is related only indirectly to the intensity of the key light. It is more the direct outcome of the colors, the textures, and the luminance of the scene. The whitest white can be three stops, or more, brighter than medium gray, and the darkest black may be three and a half stops darker than medium gray. That is why a reflected-light meter, preferably a spot meter, is used to analyze these values. More and more, the waveform monitor fulfills this function. It is essential to think in terms of the brightness range to be able to intelligently interpret the light measurements.
Measuring and Evaluating Light
Although using digital cameras may not require separate light meters, cinematographers shooting on film stocks developed sophisticated methods of light-meters usage. Generally there are three types of instruments used to evaluate exposure: the incident-light meter, the reflected-light meter, and the picture monitor accompanied by the waveform monitor (when we are shooting on a digital camera). The incident-light meter is the basic tool for measuring the light value of the sources, mainly the key lights. It is impartial as to the brightness of the subject itself. The reflected-light meter, on the other hand, indicates how much light is reflected by a given surface. It also measures the brightness of translucent surfaces such as stained glass windows, lamp shades, and other light sources visible in the photographed scene. A reflected-light meter with a narrow angle of acceptance is known as a spot meter.
It is essential to remember that reflected-light meters are calibrated for medium gray of 18 percent reflectance. This medium gray standard ensures that all the reflected-light meters will react to brightness in the same manner. Remembering this basic norm allows intelligent interpretation of the reflective readings. For example, a Caucasian face has about 35 percent reflectance but a black face reflects less than 18 percent. If you blindly follow the reflected-light reading, you’ll have both of these faces showing similar brightness values. The Caucasian face will appear a bit dark and the black face a bit light. For a more faithful representation, the white face should be given half a stop to one stop more exposure and the black face should be exposed at about one-half to one stop less than indicated by the reflected-light meter. One way to make the reflected-light meter become as impartial as the incident-light meter to the subject brightness is to measure a gray card instead of the subject. Thus the reading is not biased by the lightness or darkness of the objects in the scene. When measuring a medium gray card, the card should be angled halfway between the light direction and the camera (and meter) to get the most accurate reading.
Let’s look at the particular applications of the incident-light meter first.
The incident-light meter (or simply incident meter) measures the intensity in f/stops. Once we decide on the f/stop level of a scene, we will establish the continuity of our key light values. Therefore, we will be able to work at the same f/stop throughout the scene, keeping a uniform depth of field.
Incident-light meters have a choice of light-accepting surfaces. The hemispherical plastic “light collector” in front of the light-sensitive cell roughly resembles the shape of a human face. When held in front of a person and pointed at the camera, it collects all the light and evaluates the exposure. Some cinematographers prefer using the flat disc, which makes it easier to measure one light at a time. For this purpose it is pointed at the light itself. Which method is better remains a personal choice.
From the moment we start using a meter on the set, we have to make technical and artistic decisions. Say we are shooting on a film which is rated by the manufacturer at 100 ASA. This rating requires 100 foot-candles for an exposure at f/2.8. Right away we have several options. We can use the manufacturer’s rating of ASA 100. Or we may decide to rate it at ASA 125, 150, or even 200. If we do that, our negative will be a bit thinner and the lab will have to print it at a lower printer light. Some cameramen will rate this film at 100 ASA for the day scenes and 200 ASA for the night, but they will have it all printed as if it had been all shot at 100 ASA. As a result, the night will look darker, which in this case is the intention of the cameraman. Another way to use the film is to rate the negative at ASA 200 and push it one stop in development. As a result the negative has the density recommended by the manufacturer but the light level is one-half lower; for example, for f/2.8 we needed only 50 foot-candles. The price we pay is a slightly larger grain owing to the longer development.
Exposing the film is not only a science but an art as well. How to expose different parts of a scene becomes a creative decision.
When two actors are facing each other in a scene and one of them is a stop darker than the other, who can say which is “correctly” exposed? After all, in real life four people in a room can have four different levels of illumination on their faces. One of them standing near the window in a shaft of strong sunlight will be from a purist point of view overexposed, yet this is a very realistic rendition. Another, in a dark corner, will be underexposed two stops, and still the whole scene may be perfectly acceptable.
The majority of experienced cinematographers usually measure their key lights but set all the other lights by eye. Late in the evening when the eyes get tired, it is sometimes necessary to check a few other lights as well, in order to match shots filmed earlier to create visually uniform scenes. For this purpose, the incident-light meter became a standard tool for interior cinematography.
James Crabe, ASC
For the establishing of a key light, the meter is handy. It is not a bad idea to shoot the whole sequence at f/4, for example, because lenses have a certain look at f/4, there is a certain consistency of depth of field and all that. Often-times no one has measured the first light and you end up balancing to f/8 stop, or something a lot more than what you really need. So I like a gaffer that uses a meter to measure these areas. But the rest is done by eye. I have a contrast filter but I do not use it a lot. What I sometimes do is have a pair of sunglasses with me, with a kind of neutral density. I don’t wear them a lot, because if you do, your eye adapts to that. Once in a while I just throw them on and look around and maybe I will catch something that needs adjusting.
Reading the key and establishing how different picture areas should relate to the key exposure is the interpretive way of lighting the scene. Much of it is done by the eye.
Caleb Deschanel, ASC
Basically I use the meter after I have finished lighting, as long as I know that I have got somewhere around the overall light level that I am working for. If I want to shoot at f/2.5, I sort of shackle that, and then I light just by eye, and then I go back and figure out where my exposure should be. You are much better off using your eye. Your eye is so much more sensitive. All viewing glasses are interpolated anyway. It is not as if you trust them overall. For me, I use them to make a judgment about my relationship between shadows and highlights. I don’t use them for contrast ratios. I squint to see that.
Reading the key is the most important thing to me. I read the key and then I interpret what it means. Generally I might say I want that to be hotter than
what I am reading; say it is f/5.6 and I want to overexpose that a stop or so. I make a judgment of what I see with my eyes: Is the light hot on his face or is it dark? What is my overall impression? Is it overall dark? Maybe my impression in looking at you is that it is hot, so I want that to burn out. Everybody has a different way of making judgments about things. If you have something that is within a really limited range—like shooting in the fog, when things are pretty much evened out—then generally you try to get into the medium gray area or a little hot.
Students of cinematography are often unsure of how to use the incident meter. They frequently ask where to point the meter when the key light comes from the side or from three-quarters back, or when one person is in a very bright light and the other is in shadow. Here are a few more suggestions to clarify this issue:
Vilmos Zsigmond, ASC
One way to use an incident meter is to read the shadows on the face and then determine how dark you want this face to be in relation to medium gray (one stop darker or two stops darker) and then expose accordingly. With negative stock I would not expose for highlights, unless highlights are in a large percentage of the frame. But if only 10 percent of the face is in the highlights, I would allow them to bloom out, rather than lose details in the remaining areas, because you cannot go much darker than two stops on the face. Say that I read f/2 on the darker part of the face. When I expose at f/4, I will retain details in the face and still the highlights will blow out three or more stops. But if 60 percent of the face is lit by the sun, you will not expose for the shadows. You will let the shadows go black. You always have to consider what is the important part of your picture if you cannot bring it into balance with your lighting. You just have to expose for the part which you want to see correctly exposed and allow the rest to go either white or black. You have no choice.
Caleb Deschanel, ASC
As a general rule, depending on the size of what is in frame, I usually figure that the whitest white is about four stops overexposed and the blackest black is somewhere around three to three and a half stops underexposed, depending of course on the background. I can take someone and underexpose his face two stops and put him against the black background and you would see his face really well. I could then light the background to four stops over and have the front of his face exposed exactly the same way, and you would hardly be able to see any detail in his face, because your eye cuts down that front detail. It is a really psychological thing that happens. One of the things that I did in Being There is that in order to create the blacks that I wanted, I actually overexposed the film, so the highlights were actually hotter in order to create the illusion of the blacks being blacker. It is part of the nature of contrast. If you show absolute black on the screen, it is milky. I don’t care how good the lab, there is no such thing as absolute black. Whereas if I put a spot of white light in the middle of the black, that black will appear much blacker. Certainly one of the reasons we used a lot of practical lights in Being There was to create that sense of black.
Many cinematographers work at an f/stop that facilitates the use of a zoom when needed without changing the light levels. Others like to work at very low light levels and at the corresponding wider apertures. Their reasoning is that it is better to judge lighting contrast at low levels and that the more one stops down, the more half tones and quarter tones of brightness are lost. However, films shot with a wide-open lens can be very annoying, with so much of the frame intentionally out of focus.
For the fine analysis of the various brightness ratios in the scene, a spot meter with a one-degree acceptance angle is a very useful instrument. The spot meter represents a reflected-light metering system, which measures the brightness of the subject, whereas the incident-light meter measures the light falling on the subject. A spot meter is especially useful when there are translucent objects like stained glass windows in the scene, or practical sources of light, whether windows or lamps.
Caleb Deschanel, ASC
I almost always use a spot meter for highlights, for windows, for light sources that are in the frame, and occasionally to judge shadow details. Despite the fact that they say that they are reading one degree, every spot meter is affected by what is around the measured spot. They do not totally isolate what they are reading. You really have to be careful about how much you believe it. You have to know when to believe it and when not to believe it.
Generally spot meters are used more for analyzing the brightness range of the scene than for measuring exposure.
James Crabe, ASC
I use a spot meter mostly in commercials when I am dealing with translucent things, like a glass of beer. A typical case of measuring transmitted light would be taking a reading of a stained glass window. People always use that example when talking about reflected-light meter readings, because if you go with an incident meter, there is nothing there. I don’t use the spot meter for determining exposure usually, but it is a very handy tool.
One should be very careful when using the spot meter to determine the exposure because it reads a very small portion of the subject. Yet for the purposes described here, it is an extremely valuable tool.
Ralph Woolsey, ASC
I use a spot meter a great deal. There are definite situations where only this meter gives a fast and accurate answer—for instance, in a church when photographing inaccessible stained glass windows. You often start by asking yourself, “What am I going to read to get the basic exposure?” You might measure the widest range of significant tones with a spot meter and take the average. As with any subjects which are transilluminated, including signs, video displays, transparencies, and so forth, you are really measuring the brightness range. Some extreme situations might require an ND (neutral density) filter in front of your spot meter when reading targets like a blast furnace.
Here is another situation for the use of a spot meter: Some of my students were using a camera inside a car, photographing through the windshield, but also seeing the rearview mirror in the frame. They got a larger-than-normal mirror in order to see a motorcycle officer approaching behind the car. Their exposure through the windshield was good, but the reflection in the rearview mirror was very dark. The mirror had a neutral density tint that absorbed a lot of the light, and the rear window of the car also had some tint. By taking a spot meter reading—through the rear window—of a target like a piece of paper, and then turning around and reading it again in the rearview mirror, they could have the exposure difference, which was at least a stop and a half. One way to balance the difference would be to replace the original ND mirror with a clear one. Or you could utilize some neutral density material on the windshield to balance its brightness with the rearview image as desired. And don’t forget that the apparent density of an ND material increases as you look through it at oblique angles. A spot meter will measure such differences quickly.
Another area where the spot meter has proved to be a valuable tool is in evaluating the brightness of the sky.
Vilmos Zsigmond, ASC
Basically I use a spot meter to control the sky, that is, to control the balance between the sky and the faces. During the day the relationship between the sky and the sun stays the same, but when you are doing dusk shots, the density of the sky should be maintained throughout the scene. As it gets darker, you have to reduce your lights on each take to maintain balance. You can extend your dusk this way. Dusk is the only way to shoot day-for-night that doesn’t look phony.
This brings us to the subject of light measurement on the exteriors. Here many cinematographers will use a regular-angle reflected-light meter such as a Gossen Luna-Pro, as well as an incident meter. The spot meter, which also belongs to the reflected meter category, is used for specific tasks, such as the evaluation of the sky for sunsets and dusks.
With the exception of the spot meter, reflected meters have a rather wide angle of acceptance. This means that in a long shot an actor standing before a large white wall will end up underexposed; the same actor in f
ront of a black wall will be overexposed. The reason for these variations is that the reflected-light meter tries to average the picture to medium gray. Therefore, it indicates a high f/stop number for a shot with a predominance of white, and it designates more exposure for the predominantly black frame to bring it up to the medium gray. Obviously if an optimal exposure of the face is important, we will walk up to an actor to take the reading, or we will approximate it by reading our own hand if the light levels and the flesh tones are similar. In a situation like this a spot meter would prove to be a very convenient tool.
Remembering that reflected-light meters are calibrated to give the correct exposure for medium gray, we would compare the flesh tones to medium gray and make the necessary adjustment.
The reflected-light meter is a highly interpretative tool. Yet it is frequently used by cinematographers, mainly on exteriors. Large vistas in long shots represent color and contrast over which a cinematographer has little control. If we use the incident-light meter, the reading for a desert or for a glen in a forest may be the same, but the subject matter is totally different. We can interpret it to decide on the required exposure, or we can help ourselves by using a reflected-light meter, which will react to the brightness of the background. In a situation where the foreground action is lit by lamps, we may use a combined reading of incident meter for the foreground and reflected meter for the background.