Using Aperture Priority
When do I use Aperture Priority mode and why?
Anjali Ghosh, via email
The Aperture Priority mode is a semi automated mode in which you have control over the aperture chosen by the camera. It is represented as A or Av, depending on the camera brand you use. In this mode, you have control over ISO and aperture, while the camera automatically chooses the appropriate shutterspeed depending on the scene. To fine tune exposure, you can also dial in exposure compensation and accordingly make the image brighter or darker.
The Aperture Priority mode is very useful because it allows you to control the amount of depth in your photograph. You can select a small aperture like f/8 or f/16 to maximise depth-of-field or a large aperture like f/2.8 to minimise DOF and get background blur. Furthermore, a large aperture is useful if you are shooting in low light, so that you can get a fast enough shutterspeed to handhold the photograph.
Besides controlling the depth in your image, the Aperture Priority mode is useful if you wish to get the best possible sharpness from your lens—every lens has a particular aperture at which it is sharpest. All you need to do is to test your lens at various apertures and find out when it is sharpest. Then, you can choose to use that particular aperture when optimal sharpness is of essence.