Monday, June 18, 2007
The Handheld Meter
Far from becoming obsolete, handheld exposure meters are at least as useful in the digital age as they are for film photography
Consistency is key to my livelihood, and I've touted the benefits of incident metering for some time, both in my workshops and in postings on the web. When capturing images in the field, I eliminate as many variables as possible. Incident metering affords me this advantage, allowing me to transfer an image to my CompactFlash card quicker, with more accuracy and consistency than other methods.
Many photographers become frustrated with in-camera metering inconsistencies and the need to compensate regularly. After trying the incident meter for themselves, most have come to the same realization as I have—that obtaining correct exposure can be much simpler and more consistent using a handheld incident meter than an in-camera reflected meter.
Although the reflective meters built into cameras are convenient, they're burdened with problems. In-camera meters measure the intensity of light illuminating the sensor. The light can come directly from the sun, a flash, specular highlights into the lens or reflected off elements within the frame. The in-camera reflected metering recommendation varies with the size of the subject relative to the meter pattern, background and subject tonality, and built-in algorithms. You need only shift the camera, keeping the subject in the same position within the frame, from horizontal to vertical, when using Evaluative/Matrix metering to see the meter recommendation change. More often than not, the exposure recommended will need to be altered to suit your vision of the scene: how you want the main subject to be rendered in tone relative to the background environment. I choose not to use in-camera metering in situations where experience has shown the readings to be erroneous, inconsistent or in doubt.
You can use a digital camera's histogram to check exposures after the fact, but while in-camera histograms are handy, useful tools, you don't always have the ability to stop shooting and consult the histogram to see that you have the correct exposure. Also, an in-camera histogram represents the global tonal values present in the frame; it doesn't tell us if the most significant element is appropriately exposed. You easily could be off your ideal exposure and not know that from the in-camera histogram. Isolating the element/subject/area of most importance via a selection in Photoshop and viewing the histogram therein is more beneficial in ascertaining critical exposure as it relates to the overall image.
Light meters presume all subjects are of average reflectance, often called the midtone because it falls in the middle of the zones between pure black and pure white. All light meters measure one thing: the intensity of light, be it an in-camera reading by measuring the light reflecting off a subject or an incident reading by measuring the light as it falls onto the subject.