Plugged In: In motion — Don’t let good shots pass in a blur

By Joe Kashi, for the Redoubt Reporter

Motion blur degrades image quality to a greater extent than bad gear, but good “shot discipline” can often tame these problems.

Blurring due to subject motion is the most obvious example. Motion blur occurs when the subject is moving too fast to be crisply imaged at a particular shutter speed, noticeably moving across the image area while the shutter’s open. In these situations, image-stabilization hardware is of no value — it simply compensates for the minute shaking of your body. Only a fast-enough shutter speed will help.

Subject blurring can occur with any moving subject, even windblown leaves, but it’s most common with fast-moving subjects, such as wildlife, aircraft and sports like auto racing, football and basketball. Fast-moving subjects frequently require use of a telephoto lens to magnify the relatively distant subject enough to fill the image frame. Subject blur is magnified, literally, when you’re using a telephoto lens, magnifying not only the subject’s motion but also the normal camera shake caused by your body’s tiny natural motions.

Although photographing out-door events can be challenging, indoor sporting events like school basketball games are even more difficult to photograph well. Basketball or volleyball players, for example, are usually too distant for effective use of a camera’s built-in electronic flash. Gym lights are typically too dim for fast-enough shutter speeds at normal high-quality camera settings.

This week, we’ll consider outdoor situations where there’s usually more available light and, thus, a broader range of options. In bright midday sunshine, a good starting point for proper exposure is the old “Sunny 16” rule of thumb, which suggests using the very small f/16 lens aperture and a shutter speed equal to the ISO sensitivity. Thus, at high noon on a bright summer day, your basic exposure at a camera’s typical ISO 200 base sensitivity would be a shutter speed of 1/200 second at f/16. Similarly, increasing ISO sensitivity to 400 would result in starting at a shutter speed of 1/400 second.

Now, f/16 is a very small lens opening, small enough that the sharpness of modern lenses is unavoidably reduced by diffraction. However, if we widen the lens aperture from that small f/16 starting point to the usual optimum optical range of f/4 to f/8, then we can shorten the shutter speed by an equal amount while still exposing the same amount of light on the sensor.

Every “full stop” change in lens aperture doubles or halves the area of the circular lens opening and thus doubles or halves the amount of light transmitted to the sensor. Thus, changing from f/16 to f/11 results in twice as much light reaching the sensor, and again going from f/11 to f/8 again doubles the amount of light, as does the change from f/8 to f/5.6 and from f/5.6 to f/4, etc. Going in reverse order back toward f/16 halves the amount of light with each “full stop” change. Each would be a 1 EV (Exposure Value) change and would be equivalent to doubling or halving the shutter speed.

So, if we open the lens to f/5.6 in bright summer noon sunshine, that doubles the brightness three times (2-by-2-by-2), thus the intensity of the light striking the sensor is eight times as bright. Then, for the same ISO 200 sensitivity, we can use a shutter speed only 1/8 as long (1/1600 second) while still providing enough light onto the sensor for proper exposure. That’s fast enough for practically any fast-moving subject except, perhaps, high-speed aircraft roaring overhead at an air show.

For more sedate subjects, such as grass or foliage blowing about on a windy day, you’ll likely need a shutter speed of at least 1/250 of a second, if it’s fairly windy, faster if you’re using a telephoto lens. Fast-breaking action at a football game might require shutter speeds in the 1/800 second to 1/1000 second range, or even faster. At base ISO on a cloudless summer day, these are feasible shutter speeds and lens apertures. When the sun’s lower in the sky, if it’s somewhat cloudy, or if the subject is shadowed, then a balanced combination of higher ISO sensitivity, wider lens apertures, and/or slower shutter speeds becomes necessary.

In situations where subject motion will likely blur the image, there’s little reason to be concerned about using a lens at its optimum optical settings, nor about using a camera at its base ISO settings. Instead, focus on the primary challenge to image quality — subject motion.

Set your camera to shutter priority mode (sometimes labeled as T or Tv on the mode dial) and then set a shutter speed that’s fast enough to freeze the motion of your subject. If time and circumstances permit, take a few test shots of the subject, and then magnify and examine them in playback/review mode on your rear LCD screen. Many cameras allow you to magnify images as much as 10 to 14 times in the review process. If the subject appears to be smeared from motion blur, then you’ll need to set an even faster shutter speed and test again if feasible.

Engage image-stabilization hardware if you’re using a telephoto lens. Remember, though, that stabilization hardware really doesn’t reduce blur due to subject motion and that a shutter speed fast enough to stop subject motion will likely also neutralize camera shake.

If you find a shutter speed that stops motion in your tests but requires a wide-open or nearly wide-open lens aperture, then you should consider increasing ISO sensitivity. That allows your camera to use a somewhat smaller lens aperture at the same fast shutter speed. As always, it’s a matter of finding the right combination of settings that compensates for the highest priority constraints, in this instance the need for very fast shutter speeds.

Wide, bright lens apertures tend to be less sharp, with less depth of field than midrange settings. A good 1-inch sensor camera like Panasonic’s FZ1000 or Sony’s RX10, both of which have bright, high-magnification telephoto capabilities, should be adequate at sensitivity settings up to ISO 800. Newer Micro Four-Thirds from Olympus and Panasonic work well up to ISO 1600, while better Nikon, Pentax and Fujifilm cameras with APS-C size sensors should provide acceptable results up to ISO 3200. RAW file formats allow more exposure leeway.

Auto-ISO features may be especially useful, automatically varying ISO sensitivity as needed. The most sophisticated such feature is found in Pentax digital SLR cameras as the TAv mode. This mode allows you to specify both the desired shutter speed and the desired lens aperture, with the camera then setting the ISO sensitivity as appropriate. Used knowledgeably, features like Pentax’s TAv mode are a very effective way to photograph fast-breaking action.

You’ll be able to at least partially counteract the degraded image quality that normally accompanies high ISO settings and nonoptimum lens apertures by shooting in an RAW image file format and pre-processing those images with DXO Optics Pro before final processing in Lightroom or Photoshop.

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.

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