Shutter Speed and Film Speed or ISO

Words and photography by Paul Worsley

Last month I discussed apertures and depth of field. Shutter and film speeds have a close and vital working relationship with apertures. Shutter speeds also control the amount of light that passes through but they also control how well an image can be frozen or blurred. Imagine the shutter as a curtain that opens then closes at different speeds. The longer that curtain is open the more light but also more time for movement. On a dark or cloudy day for example, you may want to shoot some crashing waves against a cliff. A shutter open for longer will give you the light you need and will also soften up the water if so desired, by the constant movement of the ocean. If you wanted it frozen, you would quicken your shutter speed. This is where your aperture and film speed come into play.

Opening up your aperture will let in the light you may need whilst increasing your film speed and ISO will give you even more light if you still need it.

There are a few basic rules that apply to film or ISO speeds. The higher the number, the more light sensitive it is. If you are using 800 ISO there will be a noticeable amount of grain or noise as opposed to using 100 ISO.

Shutter speeds are many and varied, but here are some general guidelines. If you are steady enough you can hand hold your camera at a very still subject at 1/20th of a second but this is not really recommended, especially with a larger lens so use a tripod for that or slower speeds. 1/125th sec will freeze a subject that is still but will blur slightly where there is movement eg, a guitarist’s hand. 1/500th sec will pretty much freeze any fast moving subject whereas 1/1000th sec and more will freeze just about anything bar a bullet or a hummingbirds wings. Some cameras have 10/000th sec, which sounds impressive but I have never used anything faster than 1/2000th sec, besides you can freeze a bullet with a flash. The speed of light still beats a bullet any day of the week!