Tuesday, December 10, 2013
Sharpness The Deadly Dozen
Defeat these threats to sharp photos and create images that get optimum sharpness from any camera and lens
There's no question that lenses aren't at their sharpest when shot wide open. But as lenses have improved, sharpness at maximum aperture has gotten better. Also, modern lenses become excellent stopped down as little as one stop from maximum. Yet, many photographers fear maximum apertures and consistently stop down their lenses to ƒ/16 or smaller. That results in slow shutter speeds and increased diffraction, which reduce sharpness either on or off a tripod. Wide apertures give you the option of fast shutter speeds, which minimizes camera movement during exposure, plus the contrast of a sharp subject against an out-of-focus background makes the subject look sharper.
It's better to have a sharp photo with a little noise than a soft photo with no noise.
11 The Diffraction Challenge.
This was explained in detail in "Limiting Diffraction" in the October issue of OP (you can also find it at www.outdoorphotographer.com). Years ago, some manufacturers made few lenses that stopped down below ƒ/16 because image sharpness fell off because of diffraction. Diffraction occurs when the light goes through a very small lens opening (small ƒ-stop). The light scatters slightly, which yields softness in the image. Most lenses show a significant drop in image sharpness as you go smaller than ƒ/22 (and some show big drops even by ƒ/22). Test your lenses to see where diffraction takes hold and your photos begin to look unsharp, and don't assume that just because your lens can go to ƒ-stops like ƒ/22 or smaller that you'll get good image quality at those ƒ-stops.
A low ISO was always the key to image quality back in the days of film and also in the early days of digital photography. Unfortunately, the impression that you have to use a low ISO has endured, even though newer digital cameras can handle higher ISOs beautifully. Every DSLR or digital interchangeable-lens mirrorless camera I've seen on the market today can shoot at ISO 400 and produce image quality exceeding the ISO 100 slide films of a few years ago, and these digital cameras handily beat the old high-ISO films. Do some quick tests, and you'll see that you can shoot at ISO 400 or 800 with excellent sharpness and overall image quality.
Rob Sheppard's new blog is www.mirrorlessnature.com, and his latest books are a series of e-books from Peachpit Press about black-and-white, color and lens choice in nature and landscape photography.
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