How Light Is Used To Create Images-4
(Electronic Flash)
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 variety:
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, except in rare instances. 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. This is sometimes needed to shoot products or groups of people.
Electronic flash is the lighting of choice for most professional studios these days and has been for decades. Learning how to use them successfully is important for any professional-type photographic situation.
