By Joe Kashi, for the Redoubt Reporter
As I wrote this week’s article on a rainy Sunday evening, I found myself reviewing dozens of intensely colorful fireweed photos taken on sunny high-summer days. I’m not ready for winter after such a nice summer, but reviewing those photos and remembering those lovely days is the next best thing. Isn’t that reason enough to photograph?
Properly exposing any image is critical, particularly with JPEG files, which have little or no capability for later correction of slightly off exposures. As little as 1/3 EV (1/3 f stop to traditional film photographers) can make or break a JPEG image. When using JPEG files directly out of the camera, you need to really nail the exposure and bracket the exposure of each important shot.
Several factors affect the accuracy of any exposure. Virtually all cameras expose a bit differently despite allegedly being set to the same ISO sensitivity, shutter speed and lens aperture. Look at images made by several different cameras and you’ll find a noticeable variation in the amount of light reaching the sensor, with each image brighter or darker than those made by other cameras.
This generally results from how each camera manufacturer decides to calibrate and set their cameras. For example, my Olympus E-M5 Micro Four-Thirds cameras generally require that I set a -0.7EV exposure compensation for best results in most circumstances. If I had used that camera at its factory default settings, most of the images would seem overexposed and too light directly out of the camera.
That’s not a fatal problem with correctable RAW images, but results in serious degradation of JPEG images. Even with RAW files, though, overexposing the image reduces the amount of highlight detail salvageable in post-processing. With the E-M5 cameras, there’s less margin to recover overexposed highlight detail while more detail can be salvaged from dark shadows.
Because each camera meters differently, you should do some informal tests with your own cameras to find the exposure compensation settings that produce the best results, particularly when using JPEG files straight out of the camera. Use those settings when encountering similar situations. Exposure compensation can be adjusted on most midtier and better cameras by turning the wheel control or arrow control that’s dedicated to exposure compensation. It’s likely different with each camera model, so you’ll need to check your manual.
Your optimum exposure will also vary depending on how you or the manufacturer set the camera’s metering. For most casual photographers, the default multiarea metering works best in typical circumstances. The camera simultaneously meters many different areas of the photo and then calculates the exposure that best fits the overall situation. It’s a compromise approach, but often a very workable compromise.
When using this metering method with JPEG files, though, I recommend that you bracket the exposure. A camera makes a bracketed set of exposures by taking at least three images in which the camera first takes the calculated base exposure, then an exposure that’s .7 EV brighter than the base exposure, and another that’s .7EV darker than the base exposure.
One of these image files should be close enough to your intended result, unless you’re photographing in a very bright area, like sunlit snow, or in a very dark situation that you want to remain dark in the final image. In such cases, bracketing still makes sense but you’ll want to increase the base exposure by .7 EV for bright areas and decrease the base exposure by .7 EV for dark scenes.
Most cameras allow you to choose a variety of metering patterns beyond the default multiarea setting. I generally prefer “center-weighted” exposure, a carryover from 35-mm film cameras that assumes that the center of the image is more important than the edges and sets the exposure based on the brightness of the central portion of the image. This usually works well enough but still may require exposure compensation from time to time. A third metering method, the spot exposure reading, is best avoided by casual photographers, unless they understand how to use it to precisely set highlight and shadow area exposure.
These are simply techniques to keep in mind when making photos, particularly important ones. Your intended result is the most important factor affecting your decision about how to expose a particular photo.
Although the default average metering built into your camera will usually produce an acceptable depiction of an average scene, that default metering rarely works as well in the less common lighting situations that often result in the most striking photos. For example, when fireweed is photographed in a backlit situation, such photos often look most striking when exposure compensation is set to cause a somewhat underexposed image. That darkens the foliage and emphasizes the brightly lit flowers. Sweeping vistas, on the other hand, may look unpleasantly dark with the same exposure compensation.
To generally illustrate these differences, we’ve produced several sets of photographs, each composed of three uncorrected images from a bracketed sequence, each exactly as recorded by the camera. The intermediate image is the base exposure calculated by my camera using center-weighted metering. The darker image in each set is underexposed by -.7 EV while the brighter image is overexposed by +.7 EV. You can compare all of the example sets on our website, www.redoubtreporter.wordpress.com.
There’s no hard-and-fast rule as to which exposure is best. Individual circumstances, your own camera, your personal taste and your intended result should be the determining factors.
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.