Photographically Speaking: The Exposure Triangle

Kevin Bradshaw
Kevin Bradshaw

Controlling the light. This is what the world’s most successful photographers do best.

Getting the correct exposure, not over exposed, (too much light), or under exposed, (too dark of a photo), is the battle that photographers constantly fight on each and every shot they take. We can of course put the camera on fully automatic or program mode and shoot away all day and get reasonable photo’s, ….but this does not always work?  Why?……

First we must understand that if the camera is left up to controlling the exposure it is going to measure the light coming in through the lens and automatically adjust the aperture, shutter speed, and I.S.O. to achieve a medium grey tone to the overall picture. So what does that mean if you are down at the beach one evening shooting a bridal couple with the gorgeous sunset behind them?  Sounds like a great shot doesn’t it? You line your couple up to take up about 1/3 of the frame in a beautiful romantic pose with the gorgeous South African sunset behind them and snap the shutter! You look at the image that your camera produced and find that the couple is terribly underexposed, (too dark), but the sunset is beautiful!  Not much good if you cannot tell who the couple is you think!  Your camera has attempted to get an overall medium gray tone to the photo, so to offset the bright sunset, it underexposed the couple.  This is when you realize that sooner or later you are going to have to learn how to operate your camera on fully manual mode to get these tough shots.

As the photographer you have three controls to manipulate the amount of light coming into your camera. First the size of the opening of your lens, or the aperture.  This can be likened to the iris of your eye. In the bright daylight your iris closes to limit the amount of light entering your eye, in the darkness the opposite occurs.  The next control is your shutter speed, this could be compared to blinking your eye. The faster you blink, the less light gets in, the slower you blink the more light that enters your eye.   The final control adjusts the sensitivity of your camera sensor to the light, this is referred to as the I.S.O. .  A low I.S.O. of say 100 will give you the least amount of sensitivity and the highest quality image, where a high I.S.O. of say 1600 will be much more sensitive to light, but produce a grainier image.  In the weeks to come we are going to explore these settings in greater detail, starting with the aperture setting in next week’s column.

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