Dec 27
Photo tips #3: Depth of field
There are some aspects of photography that are almost pure science. Luckily you don’t have to be able to do the math in order to take the picture - you just have to learn to understand the principle behind it. Depth of field (DOF) is one of these. DOF is the area in your image which appears to be in sharp focus - everything between yourself and the focus area is blurry (or out of focus, OOF) and everything behind the focus area is blurry.Online DOF and hyperfocal distance calculators and in-depth explanations:
- DOFmaster (DOF and hyperfocal distance)
- Nikonians (DOF and hyperfocal distance)
- Bob Atkins (DOF)
Personally, I like shallow DOF - this is often called for selective focus. The sharp area of the image is so small that you have to be very careful where you place it, otherwise you will give the impression that the whole image is blurry.
There are three things that affect the DOF - focal length, aperture and distance to subject. If we forget for a moment that all three things work together, we can say this:
- longer focal length = less DOF
- bigger aperture = less DOF
- closer to subject = less DOF
Don’t forget that when we talk about a bigger aperture, the actual number indicating the aperture is smaller. Aperture - of F-stop - is the size of the lens opening. The bigger the opening (=bigger aperture, smaller F-stop number), the more light gets to the film or sensor. This, by the way, is directly related to the shutter speed: bigger aperture, faster shutter. Smaller aperture, longer shutter. They always move in equal opposites - if the aperture is stopped down by 1, then the shutter speed is increased by 1 stop. In case you’ve ever wondered what the numbers inprinted to your lens are, they indicate the focal length (prime, or zoom range) and the maximum aperture. For example, the 70-200mm F4 lens has a zoom range from 70 to 200mm and the maximum aperture I can use with the lens is 4 at any focal length. The 17-85mm F4-5.6 zoom has a maximum aperture of F4 at the wideangle end, and F5.6 at the long end. The 100mm F2.8 macro lens is a prime lens with a largest aperture of F2.8 - perfect for those selective focus close-ups!
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