Wednesday, April 18, 2007

Depth of Field article - Ron Bigelow

Ron Bigelow has a series of excellent technical articles on photography. A recent one which has been educational to me is his article titled Depth of Field -- Part I.

In the article he gives a good explanation of how DOF works and what factors contribute.

A couple of interesting things for me were:

1. DOF is not absolute for a given apperture, focal length and subject distance. There is only one plane of focus and the extent of areas in front of and behind that plane that are in apparent sharp focus, depends on the size of the print or image display and also the viewing distance.

Small prints will have larger DOF as will downsized jpgs. That is why web sized images at f/1.4 still have sufficient DOF ( a good example is using a 35mm wide open for low light candids at family gatherings destined for email.) When viewing the image at 100% or on large prints, the out of focus areas are more easily apparent.

2. For the same field of view and same apperture, a crop camera will have a larger DOF than a full frame camera. (e.g. 30D with 50mm lens vs 5D with 80mm lens.)

So in choosing you apperture, sometimes it's useful to consider the final destination of the image. If there is a chance you will want to enlarge it, consider stopping down a couple of stops...