By Joe Kashi, for the Redoubt Reporter
Making sharp photographs with crisp detail is photography’s natural starting point, but reaching that starting line often requires careful balancing of opposing factors. In other words, good “shot discipline.”
Before diving into the details, let’s list some factors that may need to be consciously thought through and balanced before pressing the shutter. This process is more important to those important, once-in-a-lifetime moments that can’t be repeated later.
- Optics: Use a sharp lens at its optimum aperture and with sufficient depth of field that everything important is acceptably sharp.
- Motion and blur: Use a shutter speed that’s fast enough for the situation, unless you’re consciously trying to blur the image for effect.
- ISO sensitivity: Wherever possible, use the lowest suitable ISO sensitivity.
- Camera settings: Turn image stabilization on or off as needed. Decide which exposure mode to use and whether to use automatic or manual focus and exposure. Optimally setting these camera functions for a particular situation warrants a separate “shot discipline” article next week.
Notice that I didn’t include a camera’s “megapixels.” Assuming you’re using a modern camera with a relatively large Micro Four-Thirds, APS-C or full-frame sensor, and that’s an increasingly high proportion of serious cameras sold since 2012, then you’ve already passed the point where the number of megapixels or sensor size makes much difference in any but the most critical professional situations. Relatively large sensors with 10 or 12 megapixels probably have more than enough potential resolution for most people.
There’s only one optimum exposure for a given scene as you envision it. That optimum exposure is just the right combination of shutter speed and lens aperture to allow a specific amount of light to strike the sensor. The correct amount of light varies, depending on the ISO sensitivity to which your camera is set and upon your desired effect. Proper exposure is rather like a three-legged stool that’s stable only when all three legs — ISO sensitivity, shutter speed and lens opening — are in balance.
Increase the ISO sensitivity and you need less light, which allows you to make photos in darker situations or to use either a faster shutter speed or a smaller lens opening that increases your depth of field, or a balanced combination of both. Sounds good if you say it fast enough, but increasing ISO sensitivity brings its own set of problems.
Those include more image noise (graininess), blurred fine detail and reduced ability to handle extremes of brightness in shadow and highlight areas. Although newer sensors do better at high ISO sensitivities, I still try to limit my ISO sensitivity to the camera’s lowest (base) regular ISO setting, usually about ISO 200, and not more than one or two EV higher (ISO 400 or ISO 800), as necessary. Sometimes, though, using a high ISO setting and dealing later with noise and reduced sharpness is the only way to get the photo and we simply have to make do. Using an RAW image format and a good pre-processing program like DXO Optics Pro helps minimize the negative effects of high ISO settings.
Using a sharp lens is obvious, but less obvious is using that lens within its optimum sharpness range whenever possible. Usually, optimum sharpness is found at intermediate lens settings, in the range of f/4 to f/5.6 for Micro Four-Thirds lenses, and about f/5.6 to f/8 for lenses used with larger APS-C and full-frame cameras. Although good lens reviews, such as the sharpness “field maps” at sites like http://www.imaging-resource.com and http://www.dxomark.com can provide a good general indication of your lens’ optimum range, it’s best to do some informal personal tests of your own gear, as well.
Theoretically, a perfect lens is sharpest at its widest, brightest aperture, but that’s never entirely true in practice because of the cost and difficulty of actually constructing a “perfect” lens. Every lens contains at least some imperfections, called aberrations, which improve when the lens is closed from its widest opening, with improvement especially noticeable toward the corners.
Close the lens too much, though, and an unavoidable physical problem, diffraction, quickly degrades sharpness and crisp rendering. Diffraction usually begins to reduce image quality at about f/8 for Micro Four-Thirds lenses and about f/8 to f/11 for APS-C and full-frame lenses.
What seems most unfair is that we sometimes need more depth of field, the area of sharp focus in front and behind the main focus point. Greater depth of field requires smaller lens openings while very shallow depth of field requires a very wide, bright lens aperture.
Thus, the depth of field needed for a particular photo may force you to use a particular lens aperture, even if it’s not a setting where your lens is at its best. Great depth of field resulting from a small lens aperture is needed when making landscape photographs where both foreground and background areas should be sharp. On the other hand, a portrait photographer usually cares little about great depth of field, preferring that everything but the subject’s face be out of focus in order to avoid distracting sharp detail in other areas.
That brings us to the third leg of exposure, the right shutter speed. Generally, faster shutter speeds are better unless you’re trying for a dreamy blurred effect. The typical rule for a 35-mm film camera, what we would now term a “full-frame” digital camera, was that a handheld photograph should be taken at a shutter speed at least as fast as the focal length of the lens used. That meant a shutter speed of 1/60 second or faster when using a 50-mm standard lens, and at least 1/125 second when using a modestly magnifying telephoto lens.
It’s not quite that simple anymore. As lenses become sharper and sensors become smaller, subtle motion blurring is more evident, reducing the crispness that makes a sharp photograph satisfying. Further, sensors smaller than “full-frame” 35-mm require even faster shutter speeds to reduce motion blur due to minute body motion to acceptable levels. A 50-mm lens used on a Micro Four-Thirds camera isn’t a standard lens anymore. Instead, it acts optically like a 100-mm telephoto on that smaller sensor, magnifying any motion blur and requiring a 1/100 second or faster shutter speed to neutralize camera shake caused by minute body motions.
Image-stabilization hardware doesn’t always help. Indeed, my own recent tests, not to mention Internet lore, suggest that image stabilization sometimes makes motion blurring worse. In our final “shot discipline” article next week, we’ll consider when to use or turn off image stabilization, autofocus and other camera functions that we too often take for granted.
Local attorney Joe Kashi received his bachelor’s and master’s degrees from MIT and his law degree from Georgetown University. He has published many articles about computer technology, law practice and digital photography in national media since 1990. Many of his technology and photography articles can be accessed through his website, http://www.kashilaw.com.