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Commentary

Why use electronic flash?

-Cont'd from HOME

The fact is that good lighting is not always available. And good lighting is one of the requisites for good photography. You can and sometimes must make do with what you find, for all the reasons we discuss under the general subject of lighting. But control of light, indoors and out, is a mark of the accomplished photographer (that includes the landscapists who use only natural light, and rearrange their lives to meet Earth’s demands).

We use auxiliary lighting to balance existing illumination when the natural or ambient artificial light is extremely low or high in contrast, or when there is simply not enough light for practical picture taking.

At times, the artificial light can be totally dominant and completely under the photographer’s control. Done professionally, total artificial lighting calls for a fair amount of electronic or tungsten (quartz) equipment, setup time and photographic savvy. It is simpler and quicker, and closer to the reality of the average amateur, to learn to work with ambient light in combination with the common, small flash units that most amateurs have available.

Electronic flash is sometimes the sure way to capture a fast-breaking event, when light levels can be uncertain or too low for adequate shutter speeds. If the ambient reading calls for a shutter speed of 1/125 or 1/60 of a second, it’s sometimes safer to rely on your flash with its fast exposure time to freeze the action you are trying to report.

What is electronic flash anyway?

Electronic flash is, effectively, bottled lightning. A volume of energy is stored in a capacitor -- more or less energy, depending upon the size and type of electronic flash unit. At the discretion of the photographer (when you hit the shutter release, usually) that pent-up energy is discharged through a gas-filled tube, exciting all the ticklish molecules in the inert gas and creating a burst of light.

In its nature, the duration of that flash is very brief. Early, high-energy units were spectacularly quick, on the order of brevity of freezing a bullet in mid-air. Today’s portable units are much slower, from 1/1000 to 1/2000 of a second to as slow as 1/800 of a second. Even so, they are many times faster than most camera shutter speeds. (Some of today’s shutters rival flash speeds).

Before the digital revolution, most cameras were equipped with a focal plane shutter requiring a shutter speed of 1/60 of a second or lower, usually, to safely record the flash exposure across the film surface. These days, digital cameras allow faster flash sync speeds.

Most of today’s flash units come with a sensor, a thyristor or other system which measures the amount of light being emitted, and stops the output when it reaches a predetermined, dialed-in level. But in order to understand what’s happening there, we have to examine the basic physics of flash.

In spite of cultural relativity, there are some universals. One of them is our old friend, the inverse square rule: Light Diminishes According to the Square of the Distance, now and forevermore. Using this law, we can gain freedom from computer dependence and figure out our own camera settings, if we want to.

We can calculate the exposure setting for the camera, based on our ISO, the amount of light that particular flash unit can produce, and the distance from the light source to the subject. The combination of ISO and flash output is represented by a guide number, which is used in the calculations. There is a formula for the proper f-stop:

Guide Number Formula

f-stop = flash to subject distance in feet
10ft = f8
Your Guide Number = 80

To determine your guide number, you can make a series of test exposures at a known distance (10 feet makes your arithmetic easier) and select your best exposure. If the optimum exposure is at f8 at 10 feet, the guide number is 80.

Do your testing in a reasonably sized room for average conditions of reflectance, after making a few test exposures, examine the skin tones and/or a color test target, or you can use a flash meter to test the unit at ten feet (you can rent one, or borrow one from that friend who has all the gadgets.

The starting point in using flash is, of course, with the flash on the camera. It’s basic. It is also a tool of last resort, because it produces nasty light. Flash-on-camera lighting creates a flattened view of the world: all the contours, all the shadings that give dimension to a photograph, are washed away. The shadow from direct flash has a hard edge, particularly if a person is near the background. If your camera has a built-in pop-up flash, it can be used for supplementary, fill flash. But you should have a separate, self-powered unit for more sophisticated results. The rule is, avoid direct flash when practical, because the light is not attractive. The exception to the rule is when on-camera flash is used as a fill light, in direct sunlight (or in a multiple-flash setup). Your fill light should be lower in intensity than the main light(Earth has only one sun, remember?).

Read your basic exposure, with the camera or auxiliary meter, and set the flash to produce one to two stops less light than the basic exposure. Remember that you may be working at 1/60 or less. That may mean a rather small lens opening, or a change to a lower ISO. If you are working at f16 or f22 you may be at maximum output for the flash, and can simply fire away. Okay, scratch the direct flash. Now what?

Now it gets interesting. But it could mean some equipment upgrades.Alternatives include diffused flash on camera, bounce light, diffused or direct off-camera flash, and multiple flash. The simplest of these is diffusion or a combination of diffusion and bounce. A lot depends upon that neat little thyristor that eliminates the calculations and guesswork.

Diffused flash on camera can be as simple as using a doubled handkerchief or taping a square of frosted acetate in front of the flash lens. There are also store-bought diffusion domes that slip over the flash. However you do it, the idea is to diffuse the light -- to reduce the hard shadows of a point source, and soften the effective image.

Bounce light can also operate right at the camera, but it requires a flash head that swivels. Up is basic, to the side is also handy. The idea is to direct the flash onto the ceiling or wall and ceiling combination, or just the wall, so that the subject is illuminated by the light that caroms off the reflector. The result is a light which can be relatively directional, but quite diffused.

If your handy thyristor works in this mode, you’re home free. If not, you’ll have to do a manual setting. Figure the distance the light must travel from camera to reflector to subject back to camera, and discount at least a stop for loss of light by absorption and scatter. Bracket exposures while you’re testing.

There’s a law of physics that applies to bounce light, also: The Angle of Reflectance is Equal to the Angle of Incidence.

For a demonstration of that, ask any pool player. What that means is that a light bounced straight up will come straight down, and you will have a face full of shadows. And a light bounced at a 45 degree angle off an eight foot ceiling will probably fall behind a subject six feet away. Setting the angle of the light can be critical.

The big problem with bounce flash is a tendency toward deep shadows in eye sockets and under chins. An answer is a 3X5 card taped to the back of the flash, to kick some of the light forward, into the faces. It’s a down and dirty, low tech trick that works -- a file card and a rubber band will do.

I use a white card in the back of a diffuser dome to kick light forward rather than back towards the photographer, to make the dome just a tad more efficient. But the dome is the most effective simple piece of equipment I use. I have domes glued to each flash unit -- used straight on, the loss of light is negligible. In bounce position, it’s very effective and simple.

Off-camera flash, diffused or direct, takes a giant step forward in the feel of the photograph. It calls for a remote connector, a flex or extension cord from flash unit to camera. The more sophisticated the flash system, the more directly it is linked electronically to the camera, the more complicated the remote system gets. Details need to be worked out individually, depending on your equipment and setup. You’ve got to study the manual that comes with the camera and the flash to really get this right -- intuitive ( i.e., guessing ) won’t cut it here.

The idea is to control the angle of the light, and direction of the flash.The same rules apply to this use of light as in static-light portraiture: the starting place is 45 degrees to the side and 45 degrees up from eye level. Getting the light off and up adds dimension and shape to the subject, and can usually throw the shadow behind the subject rather than onto the image background.

The same concept works with a diffuser on the flash -- the light is still directional, but softer. If your flash unit has a fixed head, the only way you can produce a bounce effect is by taking the unit off the camera. It also allows you to bounce off a wall or partition, either directly as a light source or counter to the ambient light as a fill.

Multiple flash is possible with small units, but it takes some thinking about and practice. Even the mid-sized units can be adapted to light stands with photo-sensitive triggers, to be used with the on-camera flash in a relatively inexpensive portable lighting kit. It won’t light an auditorium, but it is wonderfully effective on the 6 to 10 foot portrait and small group photos.