Aperture Priority (Av) mode
Aperture Priority (A) mode enables you to choose the lens aperture. Your camera then automatically sets the shutter speed that will give the correct exposure.
This is useful in situations where you want precise control over depth of field. Shallow depth of field means only subjects close to your camera are sharp, while more distant objects are out of focus. Large depth of field means everything is sharp, from nearby objects to the far distance.
Depth of field changes according to the lens aperture, the focal length of the lens (the zoom setting) and the focused distance.
Shallow depth of field is good for isolating portrait subjects sharply against a blurred background, while large depth of field is good for close-ups and landscapes, where you want everything sharp.
If you choose a wide aperture (a low f-number), it will result in reduced depth of field but faster shutter speeds because the lens is allowing more light through to the sensor.
If you choose a small aperture, you will get a greater depth of field, but slower shutter speeds (because less light is now reaching the sensor).
If you want a large depth of field and therefore choose a small lens aperture, you need to keep an eye on the shutter speeds because they could become so low that you risk camera shake.
That’s one reason why professional landscape photographers use tripods – they’re using small lens apertures to get maximum depth of field so nearby objects and the distant horizon are sharp.
You may want to bear in mind that lenses don’t give their sharpest results at the extreme ends of their aperture ranges. At maximum aperture your photographs are likely to look slightly softer than if you stop it down to f/5.6 or f/8. Similarly, at f/16 – and certainly by f22 – the sharpness will begin to diminish again.
As a rule, it’s more important to get the best shot pictorially, so if you need a wide or small aperture to achieve that shot, don’t worry about it.
Generally, though, the aperture range f/5.6 – 11 is best when depth of field isn’t an issue, but you do want to be sure you’re getting the best sharpness.
Lens aperture and focal length
You can set Aperture Priority mode by turning your camera’s Mode dial to A. Press the shutter button halfway down to activate the exposure meter, then turn the Command dial.
This alters the f-number on the camera’s status panel or LCD. The maximum aperture corresponds with the lowest number and depends on the lens and its zoom setting.
Most DSLR kit lenses have a maximum aperture of f3.5 at the wide-angle end of the zoom range and f5.6 at the maximum telephoto setting. In this shot, the lens was originally set to 28mm equivalent and full aperture (f3.5).
We then zoomed in to 50mm equivalent, where the lens’s maximum aperture was f4. The camera made the adjustment automatically.
PAGE 1: Digital camera modes explained – Program Exposure mode
PAGE 2: Digital camera modes explained – Aperture Priority mode
PAGE 3: Digital camera modes explained – Shutter Priority mode
PAGE 4: Digital camera modes explained – Manual mode