Tuesday, June 5, 2007
The Case For A Light Meter
There's no substitute for getting the right exposure, and there's no better tool for that than a precision handheld meter
It's a simple rule: The exposure has to be correct. That's it. Period. If the exposure is off, no amount of postproduction Photoshop wizardry will bring it back. Of course, we've all heard about the power of a RAW file and how you can massage the RAW processing to fix exposure problems, but really, the whole “fix it down the line” way of thinking is a fallacy. Now, I'm sure someone will read this and shake their head as they think back to an image that was “saved” through RAW processing, but to that I simply say, think of how much better it could have been if you didn't have to save it.
RAW workflow has generated a certain amount of laziness among photographers because of the early proclamations about exposure latitude. Shooting transparency film gives you almost no latitude for error, and color negative only slightly more, so when we started shooting digitally, it suddenly seemed that we could afford to slack off a bit. If you blew it, just fix it in post. Those “fixed” images are now relegated to a CD on the shelf because the fixes have resulted in files that lack depth, exhibit banding and, generally speaking, aren't professional-quality.
There's a simple reason why you can't rely on fixing an image that's not properly exposed. If the detail is lost at the high end or the low end, no amount of Photoshop magic can bring it back. Miss the exposure by a stop, and the highlights and shadows are all shifted by that stop. Detail that falls out of the range is gone and it's not coming back.
Really, there's no reason in the world why anyone should have a digital image that isn't properly exposed. D-SLRs have more accurate tools for evaluating exposure than film shooters could have imagined. Press the button, access the histogram and you can instantly see the mathematical representation of the full range of tones in the image.
The histogram doesn't lie. You have it or you don't. But while the histogram is a tool that shows you graphically exactly how the image is being recorded, its shortcoming is that you're looking at an image that you shot. Past tense. If your subject isn't moving, you can make an adjustment and reshoot, but if the subject isn't stationary, you missed it.
So as much as the histogram is an excellent tool for evaluating an exposure you just made, you need to use a different tool to establish the proper exposure before you shoot. The ideal predictive tool is the light meter. If you ever hear anyone say that light meters are obsolete in the digital age, see if you can buy theirs cheap. A good meter is at least as important if not more important to use when you're shooting digital.