You probably realize that a small aperture will provide you with the most depth-of-field, but stopping ALL the way down to your smallest aperture (usually the largest number, i.e., f/16, f/22, etc.) is not typically a good idea. Many lenses perform best at one or two stops shy of their smallest aperture. As you stop down from there, performance suffers. This is because of diffraction.
Sometimes you need more depth-of-field and when you do, you have no choice but to stop down (or focus stack at a larger aperture, but that's a topic for another presentation.)
It's okay to stop down when you need to, but just keep in mind that stopping ALL the way down will usually degrade image quality.
Simply put, diffraction is a phenomena that occurs with light when it interacts with an obstacle. (You’ve probably seen light diffraction patterns on the backs of DVDs, or in water molecules in the air.) If you stop all the way down to your smallest aperture, diffraction can cause your images to lose their sharpness.
ABOUT THE AUTHOR
Scott Bourne is a member of The Board Of Advisors at Macphun, an Olympus Visionary and a professional wildlife photographer, author and lecturer who specializes in birds. He was one of the founders of This Week In Photo, Founded Photofocus.com and is co-founder of the new Photo Podcast Network (photopodcasts.com.)
Scott is a regular contributor to several photography related blogs and podcasts and is the author of 11 photography books.
Scott is available to speak to your birding group, photography group and for both private and small group bird photography workshops. For more information on engaging Scott as a speaker or workshop leader, or for image licensing and print information, e-mail email@example.com.