Plugged In: Light exposed — Good shots on the spot

By Joe Kashi, for the Redoubt Reporter

Unusual situations often fool the automatic metering of any camera, which is tuned for routine conditions. Those same unusual conditions, though, often result in the most striking and beautiful photos if you have the skill to capture the moment.

One of the most famous and valuable American fine art photographs of all time, Ansel Adams’ “Moonrise, Hernandez, New Mexico, 1941,” is an excellent example of why good technical skills can make or break a memorable image. Original prints of “Moonrise” have sold for as much as $609,000 at Sotheby’s auctions and finally provided Adams with financial security after a lifetime of struggle.

Properly printed, “Moonrise” is a beautiful and powerful image of a small town in the rural U.S. West just before World War II. Copyright law and newsprint limitations don’t allow us to adequately reproduce the photo here, but I urge you to find and study a quality reproduction.

Out of curiosity, I looked at the current town of Hernandez with Google Streetview. I prefer Adams’s 1941 original. Modern Hernandez looks like just another rundown rural town that’s gained a four-lane road, some big box stores and power lines, and, in the process, lost its charm.

Adams had less than a minute to recognize and visualize the photo, stop and park his truck, set up a cumbersome 8-by-10-inch view camera on a tripod atop his truck, estimate the correct exposure without a meter, compose and manually focus the photograph and take a single image before the sun dropped below the horizon and the cemetery’s crosses ceased to glow so brilliantly. Most of us couldn’t properly take that photo in less than a minute with a fast handheld digital camera.

Most digital cameras set to some automatic mode would have been completely fooled by the large expanses of dark foreground and sky. If Adams had made his exposure using a modern digital camera and its default metering, the photo would have failed. The full moon, brilliant clouds on the horizon and small white crosses, all highlights critical to the impact of that photo, would have been so overexposed by a typically metered digital exposure that the critical highlight detail would have been irretrievably lost.

Adams’ unmetered exposure was “spot-on,” though, because he already knew the inherent brightness of the full moon, the brightest and most important highlight. Already knowing the correct exposure for the brightest highlight in which detail must be retained, he was able to work backward to determine the correct overall exposure.

Once you’ve gained some experience and knowledge, you’ll find that spot metering is the most precise approach to determining proper exposure in unusual, demanding circumstances like “Moonrise.” A spot meter precisely measures a very small area, such as a face, or the darkest shadows and brightest highlights that must retain detail in the final image. That makes spot metering ideal for high-precision photography.

Spot metering is not new. In the 1970s, handheld spot meters were commonly used by serious photographers. In fact, I still have my Pentax spot meter. Modern, upper-tier digital cameras often include one or more spot-metering exposure modes. My Olympus OM-D E-M5, in fact, has three different spot-metering modes, one intended for normal measurement, a mode intended to measure an important highlight and then automatically calculate the correct exposure, and a mode that measures the darkest shadow requiring good detail.

You may recall from a recent article that a camera’s typical automatic metering assumes that it’s measuring a neutral middle grey and sets exposure to render whatever it’s pointed at as a middle gray. That usually works, but exposure compensation is required to correct exposure readings metered off bright subjects like a snowy landscape or dark subjects like a spruce forest.

Because it measures such a small area, spot metering must be used carefully. If you spot meter a highlight area, then you’ll need to give more exposure than indicated. When measuring a Caucasian human face or a cloudless sky, adjust your camera to give a full +1 EV more exposure than indicated. A spot-metered exposure taken of snow in bright sunshine requires a subject brightness compensation of +2 EV more exposure.

Conversely, darker subjects require less light than indicated by spot metering. Darker human skin should usually be compensated by -1 EV reduced exposure while very dark shadow areas require -2 EV exposure reduction.

Remember that a 1 EV change is equal to doubling or halving exposure by either doubling or halving the shutter speed or by using a lens aperture that’s a full “stop” brighter or darker. For example, by using a wider, brighter lens aperture of, say, f/5.6 rather than the indicated f/8 or f/4, you are doubling exposure. You halve exposure by using a smaller than indicated aperture, for example, f/8 rather than the indicated f/5.6.

How would this work in practice? With my Olympus E-M5, for example, I would typically decide that the highlights are both the most fragile and the most important part of the image and expose for the highlights, letting shadows fall where they may. I’ve found that it’s easier to retrieve usable detail from too-dark shadows than from overexposed highlights. I would spot meter the most important highlight and then increase exposure by +2 EV. If the light is very contrasty, with deep shadows that I decided were important, then I might instead spot meter the deep shadow area and decrease exposure by -1.7 EV to -2 EV.

Much of the above should ring a bell with photographers familiar with Ansel Adams’ Zone System. Digital spot-metering exposure techniques differ only slightly from film photography.

With some upper-tier cameras, like the Olympus, though, there are specific spot-metering modes specifically intended for metering highlights or shadows. After some testing to assure myself of how it works, I could just set the highlight spot-metering mode, meter just the highlight, and let the camera do the exposure compensation. The same is true for the shadow-biased spot-metering mode.

If you want the greatest degree of precision and control, though, spot meter the brightest highlight in which you want detail. Write down that exposure. Do the same for the darkest shadow area in which you want good detail. Calculate the difference in EV between the two readings. You may decide to split the difference and set an intermediate exposure setting, perhaps slightly biased additionally toward either shadows or highlights as the situation warrants.

In uncertain or demanding circumstances, bracketing your exposures always makes sense as additional insurance. Images with an exceptionally broad range between highlight and shadow exposure may benefit from so-called “HDR,” high-dynamic range techniques, but those are beyond the scope of this article. Some cameras can automatically make HDR exposures, but it’s best to reserve HDR for those situations where it’s really needed.

Local attorney Joe Kashi received 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.

1 Comment

Filed under photography, Plugged in

One response to “Plugged In: Light exposed — Good shots on the spot

  1. jack

    another excellent paper, keep it up, and thank you

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