Anyone who owns a camera will be familiar with the Auto mode setting. This mode is great for point and shoot cameras, but can produce unwanted results on Digital SLR cameras.
Auto mode looks at your image and automatically adjusts it according to what the camera thinks it should look like. This includes adjusting white balance, sharpness, exposure, colour balance etc…
I am not saying never use auto mode, but once you figure out your camera settings you may never want to use it again. Lets look at some of the different modes you can and definitely should be using:
A or AV (Aperture Priority Mode)
Aperture priority mode allows you to adjust the aperture and lets the camera automatically determine the shutter speed. This allows you to change the depth of field for the images. With the aperture wide open (F2.8), the subject will usually be in focus with the background blurred out. This is called a bokeh effect.
When the aperture is smaller (F8 or higher), your image will be in complete focus. Using this mode allows you to add some artistic effects to your images.
S or Tv (Shutter Priority Mode)
Shutter priority mode allows you to adjust the shutter speed manually while the camera adjusts the aperture. This mode is great for situations where you are shooting a moving object. You can adjust the shutter speed to 1/500 seconds and the aperture will automatically adjust.
Generally the higher you adjust your shutter speed the lower your aperture will be.
A great exercise is to take a person and try out the 2 different modes to get used to being out of auto mode. You will definitely find your images looking a lot different from what you have shot in the past.