Basic Digital SLR Photography - What is Exposure?

Exposure in photography language is the "exposing" of an image sensor to light. In a digital SLR camera this involves opening up the front of the camera at the lens opening by pressing the shutter release button and allowing the light to hit the CCD or CMOS image sensor. Three things control the amount of light entering the camera.

1. First is the size or diameter of the lens opening, called the aperture. Aperture is measured as f-stops, such as f/2.8 or f/11. The smaller the number, or f-stop, the more light is allowed into the camera. So, a lens set at f/4.0 will allow much more light to hit the image sensor than a lens set at f/9.0.

2. The second is the length of time the lens is allowed to open; this is called the shutter speed. Shutter speed is measured in seconds. For instance a shutter speed of 1/40 indicates that the shutter will be open for 1/40 of a second. Obviously, the longer the shutter is open, the more light is allowed into the camera.

3. ISO is the third way to control light. ISO is a control in the camera's computer to set just how sensitive the image sensor will be to light. ISO settings range from 100 to 3200 (and higher in the newer DSLRs). With ISO, the higher the number, the more "sensitive" the image sensor is to light. So you could conceivably set your ISO at a higher number, like 1600, and take pictures in darker areas without the use of a flash. On the other hand, you can use ISO setting of lower values, like 100, when there is plenty of light.

In order for just the right amount of light to enter, there has to be a perfect combination of shutter speed, aperture and ISO. The sensor contains light receptors that are affected by the light that enters the camera during exposure. These light receptors are commonly know as pixels (short for picture element). The light entering the camera will cause the pixels to record information in the form of digital data which is converted into a photograph by a computer program, either inside your camera or in your computer after you have uploaded your images.

By controlling the three elements of exposure, Aperture, Shutter Speed, and ISO, a photographer gain a balance of color and light that is the best possible combination for that image. The goal of exposure in photography is to be able to obtain the exact effect you desire when you press the shutter button. If you get the exposure settings correct you can get many different effects and a wide range of color and brightness values.

The wider the range of color and brightness values you are able to capture, the richer and more striking the image you record. This is why it is important to know the capabilities of your digital SLR and your lens.

A majority of digital SLR users do not know the power of the tool they weild. That camera is a marvel of technology. Yes, it does have the ability to automatically record correctly exposed pictures (most of the time). However, if you know how to use the settings on your camera in different lighting situations, you will be able to create many more pleasing photos.