Excerpt from Scott Kelby's Digital Photography Book, Chapter 3, The Truth About Lenses—Use Your Lens's Sharpest Aperture
This came up in the first chapter, ‘Tips for Taking Sharp Photos,’ but this important technique naturally belongs in a chapter about lenses as well. In short, every lens has an optimal aperture—the f-stop that produces the sharpest possible photos with that lens.
What is that setting? Usually two stops above your lens's lowest possible f-stop . Suppose you have an f/2.8 lens. The optimal aperture is two stops above that, at f/5.6. Are your photos sharper at f/5.6 than when the lens is wide open at f/2.8? Yep.
Kelby's Jargon Translator
Incidentally, when you hear the term ‘wide open’ in conversations about lenses, it means shooting at the lowest possible f-stop on your lens, such as f/2.8 or f/4. Of course, you could say, ‘I shot at f/4.’ But that does not sound nearly as cool as, ‘I shot wide open at f/4.’
You may be laughing now, but just wait until you casually drop the phrase ‘wide open’ at someone's lens party. The hostess will spontaneously drop her lens hood.
