Plugged In: Look sharp — Don’t set your hopes on luck

Joe Kashi, Redoubt Reporter

Returning to “first principles,” the fundamentals underlying any subject, is often one of the best ways to ensure the correctness of more advanced practice in any field. That’s also true of digital photography, and our topic this week.

Certainly, there is no single, unvarying, correct approach to making photographs that holds true for every photo. As a first principle, though, a good default starting point is that photos generally should be sharp and correctly exposed. That usually requires a well-balanced compromise among competing technical factors.

Several factors affect optimum sharpness, including proper focus, avoiding blur due to camera shake and subject motion, a good lens used at or near its best aperture, and sufficient depth of field. As we discussed in prior articles, avoiding camera shake and subject blur are dependent upon using a shutter speed that’s fast enough for the specific condition. Photographing a high-speed air show or a racing car requires a faster shutter speed than a landscape on a still day.

Achieving proper focus is not guaranteed, even with cameras that include good autofocus. Unless used carefully, it’s common for autofocus mechanisms to focus on the wrong part of photo. Most modern cameras are difficult to accurately focus manually unless their feature set includes good “focus-peaking,” or they’ve been modified to include an after-market, split-image screen.

The traditional phase-detection focus mechanisms used in digital SLR cameras, while very fast, can go out of calibration while theoretically more-accurate contrast detection focus mechanisms found in compact cameras, smartphones and compact-system cameras can have a hard time focusing in dim light and low-contrast conditions.

Image-stabilization hardware can help a great deal to minimize camera shake but has no benefit with a fast-moving subject. Some image-stabilization systems are more effective than others, such as the “five-axis,” in-body systems used by Olympus and Sony.

Lens sharpness is endlessly disputed, resulting in slews of articles and test results. There are several first principles here, as well. A good lens on a mediocre camera will usually result in better photos than a mediocre lens on a good camera. There’s an adage that remains true — spend your money on the “glass.”

Zoom lenses are usually not as sharp as single focal-length prime lenses, although there are some exceptions. Price is not always a reliable guide to optical sharpness. I’ve seen, and personally experienced, a number of instances where the less-expensive lens performed noticeably better. Careful research and comparison before making that purchase is key.

Lenses are usually sharpest in their middle apertures, in the range of f/4 to f/8 but, again, there are exceptions and you’ll need to do some tests with your own lenses to determine its best range. Modern digital photo software helps correct some older optical problems like chromatic aberration and low contrast, but a lens that doesn’t require a lot of post-processing almost always produces better photos.

Depth of field, which can be thought of as the acceptably sharp area in front and back of the point of focus, increases as you use a smaller lens aperture. Depth of field is razor-thin at a very wide, bright lens aperture like f/1.4 or f/2, but fairly deep by f/8 to f/11. Remember, though, that overall lens sharpness inevitably declines beyond a certain point due to a physical phenomenon called diffraction.

These small apertures let in less light, so require a longer exposure, increasing the risk of camera shake. As we mentioned above, it’s a matter of finding the best tradeoff. Wide-angle lenses have more depth of field than higher-magnification telephoto lenses on the same camera. The shorter focal-length lenses used for smaller-sensor cameras likewise show more depth of field for a given magnification and lens aperture.

More depth of field is not always better. It depends on your specific image and intent. We generally prefer more depth of field for landscape shots in which both foreground and background are important and hence probably should be sharp. On the other hand, portraits tend to look better with shallow depth of field. In some situations, a wide, bright lens aperture will be used deliberately to reduce depth of field and blur the background, making the subject stand out better.

All of these first principles affect proper exposure, but that’s a topic that deserves, and needs, a separate article, so we’ll save it for another week.

Local attorney Joe Kashi received degrees from MIT and his law degree from Georgetown University. He has published articles about computer technology, law practice and digital photography in national media since 1990. Many of his articles can be accessed through his website, http://www.kashilaw.com.

1 Comment

Filed under photography, Plugged in

One response to “Plugged In: Look sharp — Don’t set your hopes on luck

  1. jack

    if using an enlarger set at 5.6 aperture , how much leeway is there in the focusing… is it measurable? like is it one or two mils?

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