Thursday, June 16, 2011

Elements of Exposure - Part I

In my last Elements of Photography entries, I discusses Elements of Composition in a two part series. In this upcoming multi-part series I will cover the basics of exposure entitled Elements of Exposure. In Part I, I will introduce this element and in the successive parts I will discuss the key elements that a photographer uses to control exposure before shifting topics to dynamic range and how we control this important element as part of the exposure process.

The Exposure Triangle
Getting your exposure right is the fundamental skill every photographer must master in order to progress. Exposure or proper exposure is the right amount of light being recorded to convey the photographer’s intent with the greatest amount of detail in the image. In photography, we measure that light in Exposure Values or commonly referred to as stops or f-stops. A stop is a doubling or halving in the amount of light. The standard camera has three ways of doubling or cutting in half the amount of light so that the proper amount of light hits the recording medium. ISO, aperture and shutter are the three controls a photographer has to affect exposure.

If you think about a triangle, we can place the exposure controls at each corner of that triangle. At the top is our ISO setting or the sensitivity of the film or sensor to the light. At the bottom two corners are the aperture, the size of the opening in the lens that the light must pass through and the shutter speed, how long the curtain in front of the recording medium is left open to the light. Our mission is to adjust each of these controls in concert to produce an image that is properly exposed with the artistic effects we desire. And it is the later part of this exposure equation that separates the professionals from the amateurs. While all modern cameras can set all three of these controls for you, it is only when you take your camera off fully-automatic mode can you dial in the appropriate setting to achieve the affect you in vision and retain proper exposure. What is proper exposure? In most cases the proper exposure combines these three setting to produce an image with details visible from the darkest shadows to the brightest highlights with the least amount of pure blacks or pure whites that the camera will allow. The proper exposure is illustrated as the dead center in the above exposure triangle. However, at times our camera may not be capable of recording the entire range of light form the brightest whites to the darkest blacks. Better known as dynamic range, the ability to capture this range by our cameras is limited. The human eye is capable of seeing a much wider dynamic range than a camera is capable of capturing. The eye can easily distinguish a dozen or more stop differences in a scene where a good DSLR camera is only capable of recording half as many and most point and shoot camera are even more limited.

Let us first review the exposure controls and how they affect our images and how we can control them to introduce certain characteristics to our images and then we will look at some techniques that allow us to reduce the dynamic range in a scene or different techniques we can use to capture a greater dynamic range.

In the next part I will cover the first of these controls, ISO.  I want to hear from you, please leave your comments, questions or topic suggestion for future blogs in the comments section.

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