Flash and Shutter Speed

An electronic flash is an important accessory that most photographers add to their kit

- Ashok Kandimalla

It provides a portable light source that can come in handy in several ways. The effect of a flash on the overall image captured can vary considerably depending on how you use the flash. This article attempts to explain a few basics of flash operation and how you can control the result by varying the shutter speed.

First, a few words on the nomenclature. An electronic flash that can be mounted on the accessory shoe of your camera is also called a flash gun or a portable strobe (Picture 1). Some manufacturers give their own names too, a couple of examples being Speedlight (Nikon) or Speedlite (Canon). A shorter form is simply ‘flash’ that we are going to use in this article. Apart from these, there are flashes used in studios. These are called studio strobes (Picture 2) or just strobes. These are large units that cannot be mounted on the shoe. They usually need an external power source (from a wall socket, for example) but now many are being powered by high-energy batteries making them more portable.

So, how does a flash work? A flash consists of a gas-filled tube into which a high voltage is discharged. This generates an arc causing an intense pulse of light of a very short duration. Typically, the duration of the flash can be as low as 1/40,000 of a second (sec), much faster than the shutter speeds that cameras offer (though there are some exceptions). The result is that shutter speed usually has no effect on flash exposure but has a significant impact on the overall exposure under some circumstances.