How Light Is Used To Create Images- IV
by William Lulow
Most photographers these days use various types of electronic flash units to provide illumination for their images. The gamut runs from simple, inexpensive on-camera flashes to large, studio ones. The studio models can cost thousands of dollars and even the smaller, professional grade portable units can be expensive as well. They are designed to replicate the effects of hotlights so, in order to use them correctly, an understanding of how light works is necessary. In the previous article I introduced the various types of electronic flash units as well as the smaller speedlight.
You can see that I’m using two “packs” and five “heads” in my small studio. My normal portrait exposures are f/11 @ 1/125th of a second at ISO 100. The packs are capable of putting out 1000 watt/seconds each, but I’m only using 250 watt/seconds on my main light, 125 on my fill-in light and 125 each on my accents and background lights. This is a”typical” setup which allows me to use all lights or as little as one, depending on the effect desired.
The relative power of these units is measured in WATT/SECONDS. (How much power is put out in a one-second flash). This is usually not very helpful when comparing studio flash units. What is helpful is knowing that if your exposure with a 500 watt/second unit is f/8, say, with a 1000 watt/second unit you would have twice the light output , allowing you to shoot at f/11. Some studio units are rated at 3200 watt/seconds or higher. This enables studio photographers to achieve a fairly high degree of light output allowing them to do things like stop motion, create stroboscopic effects, or to shoot at very small lens openings. This used to be important in the days of large, studio view cameras and slow film that required small lens openings to carry focus (lots of depth-of-field) and provide crystal clear images for advertising and catalog use.
Today, with digital camera sensors that are far more sensitive to light than film ever was, such large amounts of studio flash power are simply not needed. I have photographed products with settings of 1/125th of a second at f/22 with only 500 watt/seconds of power. The flexibility of these studio flash units allows the photographer to connect several lights (known as flash heads), to one power pack. Many of them can power three or more heads and some can power up to five heads. Of course, the more flash heads you plug into one unit, the more the power to each is diminished. This is the reason that many studios have several flash generators (packs) and multiple heads in order to cover various lighting needs.
These flash heads are all professional quality and capable of flash output of around 2400 watt/seconds. But having many flash heads and power packs are no help unless one knows how to use them. These units must also be powered by a generator and although portable, are nowhere near as easy to carry as many, lighter, off camera speedlights.
The term “speedlight” refers to smaller, less powerful flash units like the one below:
These are not professional studio flash units and, by comparison are only capable of putting out only around 50 – 100 watt/seconds of power (depending on the unit), but they are small and very handy. They can be mounted on a camera or used off-camera when mounted on a light stand or other place, but even though light modifying accessories are available for them, they probably don’t have enough power to be used with umbrellas, and setting them up with umbrellas can be tricky. Also, note the size of the light itself is quite small. Not particularly good for lighting portraits. Speedlights can also be set up to fire with radios. Some have these radios built in to them. For others, you will need to buy a radio transmitter to put on top of your camera.
You can also purchase what is called a “monolight” which is an electronic flash unit with the generator built in. Here is an example:
The beauty of these lights is that they have no cords and don’t need the extra weight of a generator.
But today, speedlights may be the only lights you would need. Unless you are doing regular studio shoots requiring one of the larger units above, one or two of these flashes may suffice for many events and other outdoor use. One should get used to using them by following some of the earlier articles detailing specific lighting effects obtainable by placing these lights in different positions. (If you wish more information, kindly refer to the blog archives). Again, use the same positioning of lights to create desired effects by referring to the articles which talk about the various classical lightings for portraits. Here again, is what my normal studio setup looks like:
Studio quality electronic flash units allow the photographer complete control over lighting. They last a long time, give constant quantity and quality of light output, are fairly easy to set up and strike and generally, make using artificial light in any setting easier than it has ever been.