The word strobe is just another way of saying “flash” but seems to be the term preferred by professional photographers. In any case, when dealing with strobe we’re manipulating very short bursts of light. The light is very intense and can expose film or a digital back in less than 1000th of a second.
There are several advantages to shooting with strobe. If you’re in a completely dark studio, you can handhold. This is because the exposure is determined by the duration of the light from the strobe (which is very short) instead of the time needed for your shutter to open and close. In fact, in a dark room or studio, the shutter speed is completely irrelevant–you need only think of aperture and of course your ISO. A good rule of thumb (for ISO around a hundred) is to keep your shutter speed fast enough–say 125th of a second–to eliminate or at least mute any stray light in the studio and then adjust the exposure by controlling the intensity of the strobe and the aperture.
Another advantage is strobe’s light color, which is daylight “neutral.” By neutral, we mean 5500 degrees Kelvin, which is about the color of the sky on a cloudy day. (The sun, which has a warmer color, and the cloudless sky, which has a cooler color, are shining together onto the back of the clouds.) This neutrality, while less important in this digital era when it’s possible to set custom white balance, was a great advantage in the days of film when tungsten lights typically had to be “gelled” to get them to have the right color. This often meant the loss of a stop or two of light.
Because strobe is instantaneous, it allows us to freeze motion. It’s perfect for drinks shots when the liquid is swirling around in the glass or even splashing out of it. It would be ideal for sports except that most strobe setups aren’t powerful enough to reach far out onto a playing field. When shooting very rapidly, when the burst of the strobe has to be as short as possible (such as when shooting a splashing drink), it’s helpful to use multiple low-power strobes instead of one high-powered one. The reason for this is that the low-power strobes’ duration is shorter, making them more effective at freezing motion.
Sometimes we want to combine strobe with continuous light. We may find hot lights perfect for providing hard warm light and strobes good for soft cool light. In a situation like this, we might set up a soft box with a strobe in it over the set and have the hot light off to the side. The easiest way to do this is simply to have the camera fire the strobe and then just hold the shutter open long enough to “burn in” the hot light. You may find it useful to take an exposure of the hot light(s) by itself and a separate shot of the strobe by itself to get a sense of what are the right settings.
One example of combining strobes with hot lights or natural light is when we want to show motion with a ghosting effect following a relatively still image. The strobe produces a still, frozen, image while ambient light, reflecting off the subject, shows motion. However, what typically happens is that the strobe fires as soon as the shutter opens and the ghosting effect follows the image that’s frozen by the strobe. Usually what’s desired instead is for the frozen image to follow the ghosting effect. To accommodate this, some fancier cameras have settings that allow you to open the shutter for a given duration and have the strobe fire at the end. In these situations the appearance of motion is controlled with the intensity of the ambient lights while the frozen image exposure is determined by the strobe.
Strobes come in various forms. The best known, of course, is the small flash attached to a camera. While often necessary in some settings where there’s no other choice, shooting with the on-camera flash is less than desirable. The light comes from the direction of the camera and creates a distinctive hardness and harshness that are unpleasant to the eye. There are a couple of ways to attenuate this problem. One is to “bounce” the light off of some larger surface such that the surface becomes the light source and provides softer light. The surface is usually a white ceiling or a wall. (Don’t try this with a colored ceiling or the shots will all take on that hue.) To accomplish this, your flash should swivel upward so you can aim it. Another half solution is to put a card or plastic reflector behind the flash so the card forms a larger surface area and creates a softer light. Third, you can attach your portable flash to a cord and hold it with one hand while firing the camera with the other. In this way you can adjust the light so it comes somewhat from the side of the subject instead of head on.
There is a time when shooting directly from the camera is advantageous: when providing fill flash. Fill flash is simply fill light used to fill in dark parts of the photograph, especially shadows. A typical scenario is when shooting a person in sunlight with the sunlight behind or overhead–in some postion from which it is casting strong shadows between the camera and the subject such that the subject, especially the subject’s face, is in shade. By hitting the front of the person with a strobe, the shadows are filled in (this is especially important when the face is in shadow) and a catch light shows up in the eyes.
There are times in professional photography when we have to adjust the light color of our strobes. In digital photography an overall color hue, warmth or coolness, is unimportant because the color balance tools in the camera (and, if need be, in post production) make it easy to make up for it with custom white balance. What you should keep in mind, however, are differences in light color since no overall balance adjustment can compensate for them. This is rarely important in outdoor scenes because the strobe is balanced for daylight, but what if you’re in a room lit with incandescent (tungsten) lights? Your first reflex may be to assume that the lights are irrelevant since you’re shooting with strobe. If you’re shooting with your on-camera flash, it is possible to eliminate the tungsten lights from the shot by keeping the shutter speed fast (set at a 125th of a second). The problem with this system is that it produces ugly shots, those typical deer-in-the-headlights kind of shots with the subject lit fiercely in the foreground and the background perfectly black. One way around this would be to light the whole room with flash heads placed in strategic locations. Unfortunately, this is often not practical. The best way to make the shot more agreeable, is to let in some of the ambient incandescent light by keeping the shutter open for a longer time, say a 30th of a second (assuming you have image stabilization and that you’re hand holding). This gives the tungsten lights time to expose the digital back. The flash then comes in and provides the extra light needed to light the front of the the subject. A problem with this system has to do with the difference in light color between the warm ambient lights and the relatively cool, daylight-balanaced, strobe. This difference can cause the picture to look artificial. To compensate for this we can gel the lights with blue gels so they match the strobe, but this isn’t usually practical since there are generally more lights than there are strobes. The usual system is to place an appropriately colored gel (in this case a warming gel) over the flash head so that it matches the color of the room lights.
While using fill flash for outdoor shots makes a lot of sense, indoor shooting with fill flash can cause red eye, the characteristic devil-like eyes shining red instead of blue or brown. Red eye is caused by the eye being dilated and by exposing the now-visible bright red retina to sudden unexpected light. The eye doesn’t have a chance to adjust to the light and shut down in time, which is why red eye rarely occurs outdoors when the pupil is made small and constricted by the ambient sunlight. To eliminate red eye, some cameras have flashes that flash once or twice before they actually expose the shot, the idea being that the light will cause the pupils to constrict. The problem is that this system delays the shot such that you may loose the photo’s potential spontaneity. Nowadays, red eye is usually eliminated with software, even in camera. If worst comes to worst, Photoshop will do the trick.
Other strobe systems are based on monolights, which are lights with their own power supplies and adjustments for light intensity. These are convenient when cords would get in the way (monolights are often battery powered and fired with a radio signal) and allow the lights to be adjusted individually for maximum control.
Most typical, at least for professional commercial photographers, is the pack-powered system of strobes in which a central power pack supplies the juice for more than one light. Power packs come with various features including the ability to adjust power to each individual light separately.
When using strobe with adjustable intensity (which is available on about everthing except, perhaps your own in-camera strobe), your first concern is what intensity to use to get the right exposure. Nowadays, it’s easy enough to fire off a shot with low power, check the exposure and make adjustments accordingly, but in the days of film, judging the exposure was much more critical.
Nowadays, many cameras have TTL (Through The Lens) metering which measures the amount of light emitted by the strobe as it reflects off the subject. The camera immediately shuts off the strobe as soon as it has projected enough light. In lieu of this, a flash meter comes in handy–if you’re buying a light meter be sure it has this capability.
When professionals shoot with strobe, they usually shoot in a darkened studio. The problem is that it’s impossible to see where the light falls from the strobes. For this reason, most professional strobe heads have modeling lights. Modeling lights are incandescent lights that are positioned in the same place as the strobe and thus give a good sense of where the light is going to land.
