DOF
One of the most important concepts in photography is understanding depth of field (DOF) and how to control this to enhance your work. DOF is best defined as the zone of sharp focus in your image. A ‘shallow’ depth of field will only focus on a small zone so that in (A) only the butterfly and surrounding leaves are focused leaving a blurred background. Conversely, an extensive depth of field will keep the subject and background in focus as in the daisies (B).
Proper use often separates ‘snapshots’ from truly striking fine art photographs. Ansel Adams was a master at extensive depth of field where all parts of his landscapes from the grassy plains to the moon and mountains were regularly tack sharp. Similarly, great portrait photographers such as Josef Karsh, often shot with a shallow depth of field giving subjects a blurry, ethereal touch when only their eyes or a bit of hair was clearly in focus.
There are three main factors affecting DOF: aperture setting, focal length of the lens, and distance from the subject.
One of the easier factors to control is aperture. All cameras, from a pro model Single Lens Reflex (SLR) to an economical point and shoot, are equipped to allow you to manipulate DOF. The camera will automatically adjust DOF when on “P” or program mode but better results are achieved if you move the setting to “A” or aperture mode.
A small aperture such as f 4.0 or f 5.6 produces a limited depth of field so that not all parts of a subject are in focus, for example only a horse’s eyes and not the mane. As your aperture increases, so does the depth of field. This is why landscapes are best taken at f11.0 or f16.0 on most cameras.
However, at higher f stops, the lens opening is smaller and requires more light. This means your camera will compensate by increasing the exposure time such as from 1/125 second at f 5.6 to 1/15 second at f 16.0; you will need a tripod for these longer exposures.
Focal length refers to the length of a lens and for most inexpensive point and shoot cameras ranges from 28 to 105 mm or more whereas for SLRs, the lenses may range from 10mm (wide angle) to 400+ mm (telephoto). The longer the length, the less depth of field. This means that if you zoom in on a subject, you are using the ‘long’ end of the range, the background will be blurry, less in focus than if you use the ‘short’ end of the lens.
Sometimes, you might not be able to choose the best length for DOF if your subject is far away. For example, if you’re photographing two friends from a distance; if you use the short end of the lens such as 30mm, then the friends will appear as a tiny speck compared to a telephoto shot at 85mm. Yet at 85mm, the picture will have less DOF than at 30mm and one person may have a blurry face.
This leads us to the last factor affecting depth of field: distance. The further you are from a subject, the greater DOF. So, if you photograph a distant skyscraper, depth of field is extensive whereas a close-up shot may only allow less than an inch of DOF.
It’s one thing to read about depth of field but in order to become proficient with your camera you need to experiment and take photographs of the same subject from different f stops, distances and lens lengths. Do this for several weeks with different types of shots such as buildings compared to people and you will quickly develop technical skill.
Mastering this technique means you’ll spend less time concentrating on all the particulars and more time focusing on the creative and unique side of photograph. Soon you will acquire your own style!
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