Depth of Field Refresher
Understanding depth of field, and how it relates to the aperture setting of your lens, is one of the most fundamental skills in photography. Indeed, being able to carefully control depth of field, along with being able to control shutter speed, are the hallmarks of a truly creative photographer. Let’s begin with a quick recap.
Depth of field refers to how to much of your image is in focus, from front to back. This is easier to illustrate than to explain – pick up most magazines, and you will see a portrait where the subject’s head (particularly their eyes) are in careful focus, while the background is blurred out.
This is an example of a shallow depth of field, and is often achieved by widening the aperture in the lens (indicated by a lower f number). In the same magazine, you might see a cityscape or landscape, where the whole image is in sharp focus, from foreground to background.
This is an example of ‘deep,’ or extended depth of field, and is usually achieved by narrowing the aperture (indicated by a higher f number). Actually, t’s not quite as simple as that, as the closer you are to something, and the closer you focus, the shallower the depth of field.
The easiest ways to control aperture are to shoot in Aperture Priority mode, as the camera then works out the right shutter speed for you; shoot in Manual mode and can you specify both aperture and shutter speed yourself, but this is not for beginners.
So, armed with this knowledge, here’s a quick guide to the kind of depth of field decisions you should be making according to different subjects and circumstances.
* Landscapes: you will find that choosing an extended depth of field will help give you sharper results from front to back. Try focusing a third of the way into the scene, too, using Manual focus (magnifying the area using Live View can help you tell whether or not you are in focus).
Don’t be tempted to use the very narrowest aperture on your lens, e.g. f/22, as this can actually result in softer images than mid-range settings. It’s also important to use a tripod with narrower apertures, unless you’re shooting in blazing sunlight; less light is being is let into the camera so it will try and choose a slower shutter speed.
* Portraits: using a wide aperture can actually make your subject appear sharper than if the whole scene was in focus. Blurring out the background is also a good way to minimise the impact of distractions.
Again though, don’t automatically go for the widest possible aperture on your lens. Very wide apertures make it harder to keep the main subject sharp and you can inadvertently soften other important areas of the face, such as the ears, or jewellery. When shooting wide, it’s absolutely essential that the AF point is bang over the eyes – the eyes simply must be in focus.
Finally, don’t forget many cameras also have a depth of field preview button, that let you ascertain the depth of field before you actually take the image. Please let me know how you get on!