Stops for the Electrician

When setting a light, an increase of one stop means doubling the light level.

The gaffer might tell the electrician to “remove a double,” “spot it in a double’s worth,” or “move the light in one stop closer.” An experienced electrician can approximate this by eye.

Contrast, Latitude, and the Zone System Contrast Ratios

The key light is angled so that the actor’s face takes on a light side (the key side) and a shadow side (the fill side). The contrast ratio is the ratio of brightness of one side to the other. As a rule, the exposure is set for the key side (this is a rule a good DP almost always breaks; we get to that in a minute). The darkness of the fill side greatly influences the emotional tone of the image. The fill light typically comes from the direction of the camera and fills in the whole face. The key light hits selected parts of the face, favoring one side. Therefore, to determine the contrast ratio you compare the light on the key side, which is key plus fill, to the shadow side, which is fill alone:

key+ fill : fill alone

If key plus fill reads 120 FC and fill alone reads 60 FC, the contrast ratio is 120:60, or 2:1. A 2:1 ratio has a one-stop difference between key plus fill and fill alone. A 2:1 ratio is relatively flat, a typical ratio for ordinary television productions.

It provides modeling while remaining bright and void of noticeably strong shadows.

With a two-stop difference, or 4:1 ratio, the fill side is distinctly darker and paints a more dramatic, chiaroscuro style. For most normal situations, the contrast ratio is kept somewhere between 2:1 and 4:1. A three-stop difference, or 9:1 ratio, puts the

sunny day typically has about a 9:1 ratio, requiring the addition of fill light to lower the contrast ratio.

Contrast Viewing Glasses

A contrast viewing glass is a dark-tinted (ND) glass that typically hangs around the gaffer’s or DP’s neck like a monocle. By viewing the scene through the glass, the gaffer can evaluate the relative values—highlights and shadow areas. The glass darkens the scene so that the highlights stand out clearly and shadow areas sink into exaggerated darkness. The glass helps evaluate if a particular highlight is too bright or a shadow too dark. On the other hand, if nothing stands out when viewed through the contrast glass, the scene has gotten too flat and monotonic; you might want to reduce the fill level, flag or net light off the backgrounds, and find places to add highlights. Contrast glasses are available in various strengths, which are meant to approximate the contrast characteristics of different film stocks. The glass becomes ineffective when it is held to the eye long enough for the eye to adjust to it. Encircle the glass with your hand so that your hand forms a lighttight seal around your eye.

Use the rest of your hand to shade the contrast glass from flare. You can also evaluate contrast without the aid of a contrast glass in the old-fashioned way, by squinting.

Gaffers also frequently use a contrast glass to check the aim of the lights. By positioning herself on the actors’ marks, a gaffer can center the aim of the light fixtures (without blinding herself) by viewing each light through the dark glass.

Similarly, a contrast glass can be used to view the movement of clouds in front of the sun on days with intermittent cloud cover. A “gaffer’s glass” or “welding glass”

is an even thicker glass, which should be used if you are looking directly at the sun.

Another way to check if clouds are about to move in front of the sun is to take off your sunglasses and view the sun’s reflection in them.

The Zone System

The human eye can see detail in a much wider range of contrast than film emulsion. Although a person looking at a scene may see detail in every shadow and every highlight, on film, anything too dark or too bright relative to the chosen exposure starts to lose definition as it approaches the extremes of the film’s latitude.

Details disappear into obscurity, and objects become either more and more bleached out or increasingly lost in blackness.

It is helpful to think of the tones in a black-and-white picture. Between pure black and pure white lies a range of values, shades of gray that define the picture.

The goal in choosing the exposure and illuminating the scene is to place those values so that they will be rendered on film as the cinematographer envisions them.

Ansel Adams, the American still photographer, invented the zone system as a tool for understanding how the values in a scene will be rendered on film. With the still film and printing process he was using, he could create 11 zones, as shown in Figure 7.5. Zone 0 is pure black and zone X is pure white. Each zone is one stop lighter than the last.

The range of brightness and darkness in which film emulsion can capture an image is known as its latitude. Each film emulsion has its own latitude characteristics

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within this 10-stop range. Cinematographers must therefore be familiar with the response of different film stocks.

Zone V, middle gray, is a very important value for determining exposure. Middle gray is 18% reflective and commonly called 18% gray. An incident light meter works by defining this midpoint in the latitude of the film. It gives an exposure reading that will make a middle-gray object appear middle gray on screen. When you define the exposure of middle gray, all the other values fall into place (to the extent of the film’s latitude). On the outer edges of the exposure latitude, the image begins to lose detail and textured areas become less defined until, at the extremes of the scale, in zones I and IX, no detail is visible and, in zones 0 and X, only pure black and pure white are seen. Ansel Adams described the appearance of each zone on film something like this:

0: Total black. With a film stock that holds blacks well, the blacks on the edge of the frame merge with the black curtains surrounding the screen.

I: Threshold of tonality but with no texture.

Figure 7.5 The 11 values of the zone system. Zone X is pure white. It is not shown here.

(From Chris Johnson, The Practical Zone System: A Simple Guide to Photographic Control, p. 31. Boston: Focal Press, 1986. Reproduced with permission of Focal Press.)

that still shows some slight detail.

III: Average dark materials and low values, showing adequate texture.

IV: Average dark foliage, dark stone, or sun shadow. Normal shadow value for white skin in sunlight.

V: Middle gray (18% reflectance). Clear northern sky near sea level, dark skin, gray stone, average weathered wood.

VI: Average white skin value in sunlight or artificial light. Light stone, shadows on snow, and sunlit landscapes.

VII: Very light skin, light gray objects, average snow with acute side lighting.

VIII: Whites with texture and delicate values. Textured snow, highlights on white skin.

IX: White without texture, approaching pure white. Snow in flat sunlight.

X: Pure white. Spectral reflections, such as sun glints or a bare light bulb.

The way the cinematographer lights the set and sets the exposure determines the various values of the scene. Suppose that the exposure outside a room with windows is five stops brighter than inside the room. If the aperture is set for the interior exposure, all details in the exterior portion of the image will fall into zone X and be completely bleached out; the edges of the windows will likely get “blown out,”

with soft fringes around them. A compromise somewhere between the exterior and the interior exposures is not much better; the interior will still be very dark and muddy (zone III) and the exterior will be hot (zone VIII). The lighting must bring the outside and the inside exposures closer together.

To look natural, the exterior should be brighter than the interior, but by two or three stops, not by five. To close the gap, you could reduce the exterior exposure two stops by gelling the windows with 0.6 neutral-density gel; you could light the inside, bringing it up to a level that is two stops less than the outside exposure; or you could combine these techniques.

Previously, I said that, as a rule, the key side of the actor’s face is set at exposure;

in other words, you would take a light reading of the key side (key plus fill) and set that exposure on the lens. In reality, a much more expressive image is created by carefully placing the values of the face in response to the natural sources within the scene and the dramatic feeling of the scene. In fact, a creative cinematographer will tell you, as a rule, never place the key side at exposure. For example, overexposing the key side by one stop while underexposing the fill side by one and a half stops gives a greater sense of light entering a space (through a window for example). In another shot, the DP might underexpose the key side of the face by one stop and let the fill side fall into near darkness, three stops underexposed. The exposures on the actors faces are balanced to some extent by other values in the image. If the scene is largely underexposed but some bright sources are within the frame, there is a reference point for the viewer’s eye. The values of backgrounds, practical lights, windows, and so on can be manipulated to place their relative intensity in the zone desired. A spot meter can be used to measure and compare reflective values, but with practice, one mostly balances levels by eye.

Negative film stocks tend to have greater latitude in overexposure than they do in underexposure. As a general rule, a neutral-gray object can be overexposed

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by as much as four stops and underexposed by up to about three stops before it becomes lost, either washed out or lost in dark shadow.

Reversal film stocks have the opposite response: They have greater latitude in underexposure and lose definition faster in overexposure. Reversal stocks tend to be more contrasty and have less latitude in general than negative stocks. Similarly, video cameras have narrow latitude: Typically, detail is well rendered only within a four- or five-stop range.

Spot Meters

A spot meter (Figure 7.6) is a reflected light meter with a very narrow field of acceptance (less than 2°). An incident meter reads the amount of light hitting the light meter, and a reflected meter reads the amount of light reflected back from the subject.

The reading depends on the reflectance of the object as well as the amount of light. From behind the camera, the DP or gaffer can sight through the meter and pick out any spot in the scene to measure, taking readings of various areas of the scene, to compare the exact values of face tones, highlights, and shadows.

Digital spot meters typically display readings in either f-stops or EV (exposure value) units. Some meters display readings only in EV units; the corresponding f-stop is found using the conversion dial on the meter. Table 7.3 shows how spot meter readings correspond to reflectance. The f-stops listed down the left side of the table

Figure 7.6 Sekonic L-608 Cine Super Zoom Master digital spot meter. A parallax-free zoom spotmeter (1°−4°) with a retractable incident lumisphere for incident light readings. Frame rates from 1 to 1000 fps can be set on the meter. Shutter angles from 5° to 270° and filter compensation can also be set on the meter. Reads in f-stops (f/0.5–f/45), foot-candles (0.12–180,000 FC), lux, Cd/m², foot-lamberts, and EV (incident and reflected). The meter notes and remembers readings using nine memory banks, handy for evaluating contrast.

(Courtesy of Seconic Professional Division, Mamiya America Corporation, Elmsford, NY.)

represent the aperture setting on the camera lens. The zones across the top of the table indicate the actual reflectance, which corresponds to spot meter readings taken off various areas of the composition.

EV units are handy because they put reflectance value on a linear scale in one-stop increments. Each EV number represents a one-stop difference in value from the last. It eliminates the mental gymnastics involved in counting on the f-stop scale. For example, if a skin tone reads f/8, and a highlight reads f/45, how many stops brighter is the highlight? Before you start counting on your fingers, let’s ask the same question in EV: The skin tone reads EV 10, the highlight EV 15; it’s easy, the difference is five stops. You can even set the ASA on the spot meter so that EV 5 represents the f-stop on the lens. By so doing, you calibrate the meter to read out in zones: EV 0–10 equal zones 0–X. EV readings are not affected by the shutter speed setting of the meter, only the ASA.

A great many DPs rely almost exclusively on a spot meter for light readings.

Knowing that the reflectance of average white skin is about zone VI and one stop lighter than 18% gray (zone V), the DP can base the f-stop on a spot reading taken off an actor’s face or a fist held out. The DP makes the necessary one-stop com-pensation mentally.

When reading the reflectance of white skin, the reading will be a half to one and a half stops brighter than the setting on the lens. Brown and olive skin falls around zone V, and dark brown and black skin values fall between zones II and IV.

When lighting and exposing black skin, the shininess of the skin plays a larger role in determining the light value than with lighter skin. Reflective glints off black skin may range up into zone VI or higher. There is a tremendous range of tonal values in human skin that the cinematographer observes and takes into account. You can

Table 7.3 Spot Meter Readings, Reflectance, and F-Stops

Aperture

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find out the exact reflectance of a particular actor by comparing the reading of the face to that of a gray card or one’s own hand.

A spot meter is particularly handy for measuring naturally luminescent sources, such as television screens, table lamps, illuminated signs, stained glass windows, neon lights, or the sky during sunrise and sunset. It is also handy for getting readings on objects that are inaccessible or far away.

Light Level

A single parameter that greatly affects all a gaffer’s major decisions is the amount of light the DP wants to film a scene. One DP I worked with always shoots ASA 50 film at a f/4 or f/5.6, indoors or out, requiring a light level of 400–600 foot-candles. To do this requires many large HMI units, heavy 4/0 cable, many large power plants, and lots of hard-working hands. Another DP shoots ASA 500 film with a very low f-stop, requiring only about 32 foot-candles of illumination. Some-times the biggest light needed might be a 2k or baby and the biggest cable is banded

#2 cable. The choice of light level affects everything: what lights to order, the power requirements, and the time and personnel needed.

Film Speed

A DP’s choice of film stock depends on many factors, including the subject matter of the film, the director’s ideas about how it should look, the types of locations, the need for matching with other stocks (matte work and opticals), and personal style of lighting and preferences about grain and color.

As illustrated in the preceding examples, the speed of the film, or ISO (also termed ASA or EI), is the primary determinant of light level. A high-speed film emulsion is very light sensitive and requires little light to gain an exposure. Slower film stocks require more light but have less apparent grain, finer resolution, and more deeply saturated colors.

The choice of film stock also affects the look of the lighting. If a slow film stock is used in an interior scene, a fairly drastic increase in light level is required, virtually replacing all natural light with brighter artificial sources. The large lights must very often be hung above the set, giving limited realistic lighting angles. Faster film stocks and lenses enable a more subdued lighting approach, with fewer and smaller artificial lights brought to bear. The small lights are easier to hide, allowing more realistic angles for the light. The cinematographer can use existing light to a greater extent.

Optimizing Lens Characteristics

Lenses tend to have the greatest clarity and definition in the middle of the f-stop scale, between f/4 and f/8. Some loss of quality occurs at the ends of the scale. For this reason, many cinematographers ask for sufficient foot-candles to work in the center of the scale. Also, because lens characteristics change very slightly at different f-stops and for simplicity of lighting, DPs often prefer to shoot all the shots for a particular sequence at the same f-stop.

Depth of field is the amount of depth that appears in focus. As the iris is opened up to lower f-stops, the depth of field decreases. (Depth of field also decreases with an increase in the focal length and a decrease in the subject’s distance to the lens.)

Depth of field is directly proportional to the f-stop. The DP who wants shallow focus with a given lens needs to use a low f-stop (f/2 or f/2.8) and, therefore, low light levels or filters must be used. Lots of depth requires a higher f-stop, necessi-tating higher light levels. Thus, the depth of field also affects the size and type of lighting fixtures used to light the scene.

Varying Exposure Time

When the camera is operated at high speed for slow-motion photography, the exposure time is decreased and the aperture must be opened up to compensate. For example, when filming a car stunt at night with multiple cameras, the working light level must be high enough to accommodate a lower f-stop setting on high-speed cameras. An f/4 (uncompensated) would force a camera running at 120 fps to expose at under an f/2. This could be accomplished with the use of super-speed lenses, which open up to about f/1.4, but could not be accomplished with many standard lenses, which typically open up to between f/2 and f/2.8, or zoom and telephoto lenses, which are slower still. Similarly, if the shutter angle is reduced, the exposure time is reduced.

When shutter speed or shutter angle is not standard, everyone must be very clear when giving f-stops as to whether the f-stop compensation has been taken into account. When giving the f-stop, you would say it is an “f/4 on the lens,” meaning that the compensation has been taken into account. If not, you should say you are giving an uncompensated reading.

The Genesis of Lighting Ideas

If ten world-class DPs each planned the lighting for a particular room, each

If ten world-class DPs each planned the lighting for a particular room, each