The first exposure meter I ever had was a little reflected light gadget made, I recall, by an outfit named Kalimar.
I was fascinated by the way a needle came alive and moved up and down to the intensity of the light around me when I pushed the meter's little button. (I was in junior high school in the Bronx at the time. I admit: it didn't take much to fascinate me.)
More than four decades later I still am measuring light in much the same way when I am about to photograph. Only now my tools are far more sophisticated (and, sad to say, far more expensive) but they rarely let me down.
If the most important thing in photography is learning to see, the second most important thing is learning to meter, i.e: to gauge exposure correctly.
Somewhere in the dim mists of photographic history someone a scientist, an artist, a shaman, whoever figured out a standardized way to measure exposure on light-sensitive materials. For our purposes today, all we have to know is that, when shooting with film, a given emulsion will react to light in a specific way. [For that matter, in manual digital shooting, in which the camera's sensitivity is calibrated in traditional film speeds, or ISOs, the same rule applies.]
As Bruce Warren notes in his seminal textbook Photography, "the definition of exposure can be given as a formula: Film Exposure=Illuminance of the image [multiplied by] Time."
Time is easy to figure out: it's the length of time one's shutter is open. "Illuminance" is something different, though. This odd-sounding word, Warren says, means "the amount of light falling on a surface, in this case the image formed on the film from light coming from the subject." Illuminance is affected by two variables: 1. Illumination, which is the amount of light falling on the subject and 2. Reflectance, which is the ability of the surface to reflect light."
All of which leads us to Bruce Warren's shorthand definition of correct exposure:
"Film exposure depends upon subject illuminance (illumination and reflectance) and camera settings (f-stop and shutter speed). If we wish to get correct exposure we must be able to measure or control all of these factors."
Sounds simple, right? [Actually, I don't think any of the above sounds simple, but I never was much for scientific formulas.]
In the real world of measuring exposure to make a picture, there are a number of things that can rise up and bite us on the rear lens element and ruin our shot. Promising to forego any further tech lingo, I'll try to run through the ones I've been able to overcome, as the result of trial-and-error, technical reading, and valuable help from expensive toys.
First up is the story of snow blindness, reading the grass, and a good grey card.
It's almost a sure bet that the first pictures you ever made in the snow did not have the crystalline brightness that prompted you to make the shot to begin with. That's because of the immutable rule of 18% reflectance.
Basically, all conventional exposure meters (those that measure light reflected off a subject) are calibrated to measure exposure as if they were reading light coming off a grey card that is reflecting 18% of the light coming to it. It's a nice average a midway point between black and whiteand one that works remarkably well, except when it doesn't.
Which is why my first snow pix stank.
That's because snow especially snow in the sun is a hell of a lot brighter than a grey piece of cardboard. Any meter reading, now matter how carefully made, will be wildly inaccurate if it is simply made by measuring light reflecting off the snow. Remember: the meter will think, "wow, this 'grey card' is in a lot of light. Frank sure doesn't need much light to make this pic, so I'll tell him to stop his lens way, way down."
The result? An underexposed snow picture in which the bright white snow will look like 18% grey slush. [Conversely, if I had read from a grey card placed in the same light as the snow, the meter would have had me open up my lens accordingly and my exposure would have resulted in a much brighter, more accurate, picture.]
My wife Judy hammered this theory into my head when we started shooting weddings together 20 years ago. "Read the grass!" she'd say, when she wasn't pointing her old Nikon F2 downward and actually making an exposure reading off...the grass...before she straightened up to make a perfect shot of the bride and groom.
Why the grass? Because it turns out that grass in shade is a fairly good substitute for a grey card. So is the [shaded] palm of your hand. Probably the most frequent error made by an amateur is underexposing pictures because his or her in-camera meter has been tricked by a bright element in the frame and caused the camera lens to let in less light than it should. Moral: Read the grass, etc., and then get over the fear that, when you straighten up and aim at your subject, your meter likely will be showing overexposure. Remember: you're the one with the real brain, not your camera.
While I'm at this: another way to get a good exposure with an in-camera meter is to walk up to your subject and literally stick the camera in his or her face to make a reading off the skin. Think about it: in such a pic, the most important element is the person. Meter for people and in most cases, especially when using bxw or color negative film, the rest will fall into place.
Still another hint, when your meter fails, etc.: remember the "sunny 16" rule. Outdoors in direct sun, you usually can get a workable exposure by setting your aperture to f.16, then simply making a fraction of your film's ISO to get a shutter speed. For example, with 125-speed film, shoot f.16 at 1/125th; with 400-speed film, the closest might be f.16 at 1/500th. [Bracketing exposure is always a good idea here.]
If sticking a camera into a subject's face is neither desirable nor practical, a good spotmeter is just the ticket. This wonderful tool lets you sight through its viewfinder and measure reflected light far away be it a vase a flowers a few feet from you, or a mountain range way off in the distance. The beauty part of a spotmeter's tiny angle of measurement is that you can make spotmeter readings off several elements of your proposed picture and accurately come to an average reading that should cover everything.
Note: this bit of help is not cheap. Current spotmeters, similar to my older Minolta Spotmeter F (pictured at right) now generally run between $350-550.
Generally, the most accurate method of measuring ambient light is through an incident light meter, usually distinguished by a white plastic globe at its top. If reflected light is the light bouncing off a subject, incident light is the light coming to a subject. An incident reading which, again, has to be made at the source, i.e.: right near your subject doesn't worry about a subject's confusing or differing reflectivity (all the 18% grey stuff). All that matters to this meter is the light showering the thing you want to shoot. If you've ever seen still and video news photographers getting ready to shoot a press conference or similar event, you may have seen one person standing at the podium holding up to his or her face a meter with a white bulb pointing toward the TV lights. The white bulb [the light gathering cone] is pointed that way to accurately measure the light hitting the podium and then translate that into an equally accurate exposure reading.
Flash photography outdoors often requires metering both the flash and the existing ambient light, especially if you want to incorporate flattering ambient light for a more natural-looking photograph. [A flash meter, like the two pictured at right, can instantaneously measure the light from a strobe or flash unit. Figure spending around $400-650.] In the color bridal portrait here, note how the couple is perfectly lit by my flash, while I also have let in enough light to register the gorgeous late afternoon shadows and sunlight. In this case I made a spotmeter reading of the darkest and lightest elements of the background, then averaged them. I then made a flashmeter reading to get a working aperture for my flash.
Say the average ambient reading for the background was f.8 at 1/250th, and the flash reading gave me a working aperture of f. 5.6. I'd set my shutter at 1/250th (since my camera's flsh sync would go that high) and my aperture at f.5.6, effectively combining elements of the ambient and flash exposure readings for a perfectly exposed shot.
Look for Bruce Warren's Photography at area bookshops. (Delmar Publishing, 576 pages, or search online.
Frank Van Riper is a Washington-based commercial and documentary photographer and author. His latest book is Talking Photography (Allworth Press), a collection of his Washington Post columns and other photography writing over the past decade. He can be reached through his website www.GVRphoto.com.