Aperture Priority Mode (often it has a symbol of ‘A’ or Av’ to indicate it’s selected)
Before going to this .. lets understand First Depth of Field,
Depth of Field (DOF) is that amount of your shot that will be in focus. Large depth of field means that most of your image will be in focus whether it’s close to your camera or far away (like the picture to the left where both the foreground and background are largely in focus – taken with an aperture of f/22).
Small (or shallow) depth of field means that only part of the image will be in focus and the rest will be fuzzy or blur. You’ll see in it that the tip of the yellow stems are in focus but even though they are only 1cm or so behind them that the petals are out of focus. This is a very shallow depth of field and was taken with an aperture of f/4.5).
When would you use Aperture Priority Mode? –
Basically this mode is used to control the DOF. If you want a shallow, select a large aperture (for example f/1.4 – ) and let the camera choose an appropriate shutter speed.
If you wanted an image with everything in focus they’d pick a smaller aperture (for example f/22) and let the camera choose an appropriate shutter speed (generally a longer one).
In most landscape photography you’ll see small aperture settings (large F numbers) selected by photographers. This ensures that from the foreground to the horizon is relatively in focus.
On the other hand in portrait photography it can be very handy to have your subject perfectly in focus but to have a nice blurry background in order to ensure that your subject is the main focal point and that other elements in the shot are not distracting. In this case you’d choose a large aperture (small F number) to ensure a shallow depth of field.
Shutter Priority Mode : (often has a symbol of Tv or S)
You need to choose shutter priority mode when you want more control over how to photograph a moving subject.
For example: photograph a racing car but want to completely freeze it so there is no motion blur, choose a fast shutter speed (say at 1/2000 like in the first shot below) and the camera would take into consideration how much light there was available and set an appropriate aperture. If instead you wanted to photograph the car but have some motion blur to illustrate how fast the car is moving you might like to choose a slower shutter speed (like the second shot below which has a shutter speed of 1/125) and the camera would choose a smaller aperture as a result.
The best way to learn about Shutter priority and Aperture Priority modes is to grab your camera, to head out with it and to experiment. Switch to Av or Tv and start playing with the different settings (taking lots of shots as you go). Particularly watch how the camera makes changes to compensate for your selections and what impact it has upon the shots that you take.
Happy Clicking …