ISO stands for International Standards Organization. Chance are you’ll never be asked what ISO means so don’t worry about memorizing what it stands for! ISO directly affects how sensitive your camera’s image sensor is to light. The higher the setting, the less light you’ll need to capture a normally-exposed picture.
Years ago, before the advent of digital cameras, all film was rated by ISO. The standard film for daytime use was ISO-100. If you wanted to take pictures of someone blowing out their birthday candles in the dark, you had to switch to a film with a higher ISO rating. Today, all you have to do is switch the camera to a higher ISO setting.
Very few beginning photographers realize their camera can take pictures in almost total darkness. Most digital cameras today have ISO settings up to 6400. The standard settings on most decent digital cameras are ISO 64, 100, 200, 400, 800, 1600, 3200, and even 6400. The 6400 setting requires very little light.
If you switch from ISO 100 to 200, you increase your camera’s sensitivity to light by 100%. In some cases you’d have too much light and need to lower the shutter speed, decrease the aperture, or both. The list below shows the relative changes to shutter speed and aperture based on the ISO settings.
ISO Shutter Speed Aperture
100 1/60 f/4
200 1/125 f/5.6
400 1/250 f/8
800 1/500 f/11
1600 1/1000 f/16
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