Understanding Your Camera: Exposure and Depth of Field

Exposure This refers to the amount of light collected by a camera’s sensor to create a photograph. It is important to gauge how much light is needed for the photo; too much light and the picture will be blown out (too bright), not enough light, and the picture will be too dark. There are three main factors that contribute to and affect exposure and depth-of-field; aperture, shutter speed, and ISO. An understanding of each and how they relate to each other is necessary to get the right amount of exposure for your subject and lighting conditions. Most modern cameras have a light meter to show how much light the sensor is collecting, and indicate the best exposure for your shot. Many cameras also have an “Auto” mode that will set aperture, shutter speed and ISO for you. To move beyond the AUTo Mode and get good photos, you need to understand exposure, framing and focus, and have the ability to manually adjust your camera’s settings to achieve the desired effect. 
Aperture This is the size of the lens opening that allows light to hit the sensor. When looking at the settings on a camera, aperture is called F-stop, and shown like this F8.0, or this f/2.8. The size of the F-Stop number is inversely related to the size of the lens opening, so lower numbers mean a larger aperture, which will let in more light to the sensor. Sometimes, the phrase “aperture value” is used instead of F-stop value. Aperture dictates what is actually in focus (depth-of-field). A low F-stop can be used to focus on a single object, blurring the background, and higher F-stop values can be used to focus on a lot of stuff at once.
Shutter Speed This regulates how long the shutter stays open to admit light to the sensor. The slower your shutter speed, the more light will be gathered by the sensor, thus exposing the photo more. Shutter speed is measured in very small increments of time; seconds and fractions of seconds. With fractions of seconds, larger denominators indicate faster shutter speed. For most hand-held photos, shutter speeds of 1/60 of a second or faster will be optimal. Because it is very difficult to hold a camera perfectly steady for any length of time, lower speeds (longer exposure time) often result in blurry photos. Some cameras come with image stabilization, which helps with camera shake. Also, using a tripod is a good idea if you need a longer exposure for your shot.
ISO This expresses the light sensitivity of a digital camera’s sensor. Film ISO is not adjusted on the camera, but film can be bought in several ISO values. Higher ISO number means the digital camera’s sensor is “getting more out of” the light it receives. Higher ISO settings are good for low-light situations, when you need the camera to make as much use of available light as possible. Lower ISO settings are preferable when there is plenty of available light. The higher the ISO, the more noise (grain, in film) you will get in your photo. Generally, it is best to use the lowest ISO setting that will also allow for proper exposure. 
Since F-stop and shutter speed affect the amount of light received by the sensor, and ISO dictates the sensor’s sensitivity to that light, they can be manipulated together for just the right exposure. 
As with any skill, good photography takes a lot of practice, all the best sports photography and wedding photography shots have been taken after learning and of course practicing for years , but the satisfaction of taking beautiful, artistic photos is well worth the trial and error.