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Friday, April 1, 2005

What Is Sharpness?


A Deeper Understanding Of Sharpness Can Help Better Control It


Selective Focus
Our eyes respond strongly to contrast, but light/dark contrast is only part of the story. You can achieve a higher degree of sharpness by selective focus, a technique where the subject is sharp and much of the rest of the photograph is deliberately out of focus. This contrast makes the sharp areas look extra-sharp, and is best achieved with wide-open apertures (small ƒ-stop numbers) and telephoto lenses.

Sharpness Tips
While these seven elements of sharpness often aren't discussed, they're valuable techniques to use to increase the quality of your own images. Follow these guidelines for sharper photos.

1) Use a tripod and lens shade to ensure you capture the brilliance
and sharpness built into
a lens.

2) Look for ways to use contrast in and around your subject.

3) Use the direction of
the light effectively.

4) Watch out for image flare.

5) Contrast sharp subjects with out-of-focus surroundings.

6) Use a larger imaging format.

7) Be aware of grain or noise issues.

Selective focus can be a real benefit when you're handholding a camera. A small aperture may mean too slow a shutter speed to keep everything sharp (especially retaining image brilliance), resulting in much depth of field perhaps, but fuzzy sharpness. It's better to get something perfectly sharp using a wider lens opening and a faster shutter speed.

The concept of sharp/unsharp contrast also can be used to make a less-sharp image look better. Bring the image into the computer, then sharpen the part that needs to be sharp as best you can. Next, select the other parts of the photo and apply a Gaussian Blur until the sharp areas contrast with the blurred areas enough so that they look sharper.

Formats
Larger film formats and more megapixels offer more sharpness in larger images. This type of sharpness is strongly related to final image size. If you only printed small photos, you'd see little difference in image quality from 35mm to 4x5, or 4 megapixels to 17. But as your image size increases, such as going to a 16x20-inch print, the contrasty edges that define sharpness will become bigger. In the case of smaller-format cameras, that means those edges will start to lose detail, dropping sharpness.

Another effect not as commonly known is related to image brilliance. Medium-and large-format cameras, as well as larger-megapixel digital cameras, often will have superior image brilliance than 35mm or lower-megapixel cameras in moderate-sized prints. Sometimes, however, this is due to medium- and large-format cameras being used almost exclusively on a tripod compared to the more casual use of 35mm-sized cameras.

Gain or Noise
An anomaly of sorts regarding sharpness appears in grain or noise. Normally, we try to get rid of those image artifacts (something that appears in an image due to the technology used) or at least minimize them. But grain (and the digital equivalent, noise) can make a photo look both less and more sharp.

When grain becomes too strong, it obscures details, making sharpness an issue. On the other hand, if a viewer sees crisp grain in a print, he or she often assumes the photo is sharper than it really is.

One reason why many photographers wanted to use Kodak's black-and-white TriX film way past the time the company wanted to discontinue it was for its unique tonal qualities. On the downside, it's a grainy film, but photographers discovered that if you made sure the grain looked very sharp when printing the film in the darkroom, the image always appeared sharp.

The same goes for digital. A camera rep had pros complaining that the latest, high-megapixel camera was less sharp than the older models. He checked and discovered that the latest camera was so clean and noise-free that these photographers were missing it. He actually had to add grain to the photos to get them to believe it, too!


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