At Earthboundlight a blog entry appeared this week to answer a reader’s question: ‘Why would you want to have an f/2.8 lens?’ Bob Johnson, the author of Earthboundlight, looked at this question from the landscape photographer’s point of view. In Ansel Adams’s days, with the big plate cameras, you needed f/64 to get the ‘grand vistas’ sharp from front to end—that’s why Ansel Adams was member of the Group f/64. Current lenses ‘only’ go to f/22 (sometimes f/32), so landscape photographers tend to use those small apertures—and a tripod, because you get long exposure time at small lens openings. Luckily landscapes tend to stay in place long enough ;-)
What Johnson did not say was that at smaller formats, you get the same depth-of-field at lower aperture numbers. That is why it is so easy (relatively!) to make macro photos with compact cameras: with their tiny sensors, they get that flower detail all sharp at full opening, where a DSLR (especially a full-frame one) must stop down to f/22 to get the same. So for a landscape to be sharp from foreground to horizon, you can make do with f/22 rather than f/64 on a DSLR—if you want it all sharp.
It gives a classical look to—especially—landscape photos to have them sharp all over. Give it a sepia toning and you’d almost believe it was a 19th century picture! But most of the time, you don’t need sharpness all over to get the effect you want: selective sharpness is much more creative. You don’t need that grass and branch in the foreground to be sharp for them to have the effect of suggesting more depth to the photo with the manor house in the background.
Selective sharpness also works in close-up photos: this minuscule blueberry flower was all you need to see sharply—it conveys the spring feeling much better with the strong bokeh (‘unsharpness’) than a picture bewilderingly full of sharp details would have done.
Both these photos were taken at f/2.8—I only have one lens that opens so widely. The wide aperture has the advantage that you get more light into the viewfinder, so you see more clearly and you (or the camera) can focus more precisely. Moreover, f/2.8 often signals professional lenses, which also have other advantages, like minimum distortion of straight lines, minimum flare, minimum chromatic aberration and other flaws. Their only disadvantages are weight (that kept me from choosing one as my standard lens)—and price…