Thursday, October 2, 2008

Photography tip: Shallow depth of field

It is my experience that the use of shallow depth of field (dof) is one of the easiest ways to impress people with your photography skills. Obviously, we're not here to impress people with our photography skills, so it's good to note that shallow dof is also a great way to isolate your subject from busy backgrounds.
The picture to the left clearly shows this latter function. Despite the fact that the background is a pretty girl with fresh-colored clothing, there is no doubt where your eyes want to go. The orange draws the attention away from the face, which would be the natural focus point in such a picture. It is the narrow dof that creates this effect. The sharpness is carefully laid in only one place in the picture. That's the 'why', now for the 'how'.
The obvious way to create shallow dof is using a wide aperture (i.e. a small f-number). The example picture was shot at f/1.8, which obviously requires a lens capable of such a wide aperture. Do not despair if you do not have such a lens however, the effect can be reached at f/4 or f/5 as well.
Focussing distance
Your depth of field is also narrowed if you approach your subject closer. If your lens or camera is not capable of wide apertures, just move in a little closer. In macro-photography, this is even considered a disadvantage, as the extreme close focussing distances do not leave room for sufficient depth of field in the picture. I allready explained that, remember?
Focal length
Finally, focal length also influences the depth of field. The longer (more tele) the focal length of your lens is, the narrower the depth of field will be. Of course, there is a rade off between focal length and focussing distance. You can calculate the your depth of field from the website given in the link below.
Don't overdo
Some people are so impressed with the wide aperture of their lens that they use it wide open all the time. Next thing you know they start complaining about lack of sharpness in user reviews. Let's face it, using a 50 mm lens at f/1.8 at 1 meter shooting distance, leaves you a depth of field of 3 cm. Nice for an orange, but hardly suited for anything bigger. Use a dof-calculator or your good judgement to choose the aperture that keeps the larger part of your subject in focus.
More resources:

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