Tuesday, March 2, 2010
Watch Out For Blowout
Exposures In All The Bright Places • Traveling With Photo Gear • Fine-Art Prints, Or Not
Exposures In All The Bright Places
Q I’m a serious amateur photographer using a Canon EOS 5D Mark II. I’ll be traveling to Antarctica next year; how can I be sure to get correct exposures in such a bright environment?
Via the Internet
A In the days of film, exposure in bright areas was always a challenge, and we’d constantly try to outthink the meter by over- or underexposing our images. It was hit or miss, and especially a problem in snow and ice environments. In the age of digital, there’s no guessing; you can be absolutely sure you have the right exposure before you leave your subject by checking the histogram on the back LCD screen.
The histogram on your camera offers two modes, a color display and a brightness display. I typically use only the latter, which graphs the number of pixels of each tonal value in the image, from true black (without detail) on the left margin to true white (white without detail) on the right. If your histogram displays many pixels lined up against the right margin, your image contains areas that are “blown out”—that is, they have no detail. The cure is to change your exposure to bring the histogram off of the right edge so there’s detail in your whitest whites. Another overexposure indicator on your camera is the “blinking highlights” option. If this mode is enabled, any area of the image that’s blown out will blink when you view it on the back LCD screen. But don’t rely only on “the blinkies.” Check your histogram to get the whole story, and adjust your exposure accordingly.
By the way, when you go to Hawai’i and photograph black lava, you’ll want to pay attention to the other end of the histogram spectrum. Anything touching the left (dark) side of the histogram will have no detail. In that case, you’d open up the exposure to solve the problem.
The histogram will help you to get the best single exposure you can. In high-contrast situations, one exposure won’t be perfect. High Dynamic Range (HDR) techniques allow you to composite a full set of exposures to render an image with complete tonal range. You may want to explore this technique and practice it before you leave for Antarctica (or Hawai’i), and you’ll find information about it in previous issues of this magazine.
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