How Light Is Used To Create Images-4
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, 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.
Here are some examples of flash generators for the studio:
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 and multiple heads in order to cover various lighting needs.
These are some sample flash heads:
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 of no use unless one knows how to use them. These units must also be powered by a generator and although portable, are no where 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 usually only around 100 watt/seconds of power, 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. One should get used to using these speedlights 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).