ASA - ISO Ambient Light Rule

If you have been taking photographs for years or just now starting there is one quick rule of thumb that is key to understanding how cameras work. I call it the Ambient Light Rule. There are two standard agencies that regulate camera speeds; in the old days film used ASA (American Standards Association) now film cameras and digital cameras use ISO (International Standards Organization) with both the higher the ASA or ISO number the faster the film or computer chip will accept light therefore allowing the camera to manipulate shutter speed and aperture opening.

Ambient Light Rule is quickly this, the faster the shutter speed (stop motion) the lower the aperture opening (depth of field). This can be changed by using a higher or lower ASA or ISO. This all depends on what kind of picture you want to take. Automatic cameras make it easy to take pictures they will adjust the shutter speed and aperture without you needing to know the Ambient Light Rule.

However sometimes it is necessary to go off automatic mode for the shot you want to take. For example, say you go to a Nascar race and you want a picture of your favorite Nascar Driver going over 200 miles per hour. In this case you may want to take your film or digital camera off auto and go with shutter preferred and choose a fast stutter speed probably at least 1/500th of a second. The faster the better, but this setting does effect how clear the items are in the foreground and background.

Another situation is when you want to take a close up and want as clear of shot that is possible. Here you may want to go with aperture preferred. In this case the higher the aperture (means the smaller the light source kind of like squinting your eyes to see better) means that you will get a sharper photograph. But the higher the aperture the slower the shutter speed. You either need more light or you may want to use a tripod.

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