We discuss the creative possibilities using different apertures to vary the depth of field to your preference.
Aperture is the most commonly applied creative control that photographers use. You probably already know that it is also a critical variable where exposure is concerned. If you are not sure about this, please refer to the previous article. We learnt that exposure is governed by 3 variables of aperture, shutter speed and ISO; and various combinations of these 3 can be used to arrive at identical exposures.
But why would you WANT to use a different combination of aperture and shutter speed to arrive at the identical exposure? Well, because apart from exposure control, aperture and shutter speed have different side effects. A change in aperture changes the ‘depth of field’ created by a lens, and this is probably to most common creative tool at the hands of a photographer.
The depth of field can simply be defined as the distance between the nearest subject of acceptable sharpness and the furthest subject of acceptable sharpness, ‘acceptable sharpness’ being the largest circle that appears as a dot but let us not get into that in a complicated way. In other words, the depth of field is that range of distance that appear nice and sharp in your photograph…further or nearer objects which fall outside of this depth of field appear blurry and out of focus. A change in the aperture setting on your lens has a direct impact on the depth of field that is created. The smaller the aperture (in other words high ‘f’ numbers such as f 11 or f 16), the longer or deeper is the depth of field; and the larger the aperture (meaning small f numbers such as f 2.8 and f 4), the shallower is the depth of field.
A shallow depth of field could be employed when shooting portraits – of course you would want the background out of focus and the subject ‘in focus’ and something like an aperture of f2 can nicely create this separation. On the other hand, a photographer shooting landscapes would probably want everything from the nearest to the furthest object in the composition to appear ‘in focus’ and therefore use an aperture of something like f22. More often than not, a shallow depth of field can give impressive results with commonplace subjects such as people and pets.
Your kit lens probably does not allow for larger apertures than f 3.5, and the 3.5 turns itself into f 5.6 when you zoom in (this happens because the aperture is a fraction of the focal length divided by diameter). A good addition to your kit as a next buy could well be a 50mm fixed focal length lens which gives you something like f2 or f1.8.
Try prioritizing the need of the hour and fix your aperture to the largest opening possible, and then use the camera meter to get the right shutter speed and ISO setting, and shoot ‘aperture priority’ for a while to get the hang of aperture control and depth of field.