Tuesday, February 1, 2005

An exposure to exposure meters


By James Booth

Throughout my articles on the basics of photography, I've emphasized getting the correct exposure. I've given you mathematical formulas and various theories for achieving the ever-elusive perfect exposure. During some of these articles, you may recall me mentioning the use of exposure meters. In this piece, I'll finally be acquainting you with this indispensable little gadget.

What it's for

What does an exposure meter do? It gives you the correct exposure for any photographic situation you'll encounter. By measuring either the light reflecting off of, or falling on the subject, the exposure meter will calculate the perfect aperture (f-stop) and/or shutter speed for every shot. Using the exposure from your meter, your shots will have perfect depth of field every time.

Different types of exposure meters

Exposure meters come in several different varieties, and can be used a couple of different ways. Light meters are designed to measure ambient light only, flash meters are used in flash photography, and combination meters perform the functions of both light and flash meters.

The simplest exposure meter is the one built into the camera. These TTL (through the lens) meters measure the reflected light coming off of the subject. Some of them are center-weighted, measuring the center section of the frame, and some use intelligent metering, measuring multiple areas of the frame and computing for what it thinks is the best exposure.

These meters typically convey the measurement in the form of a balance scale visible inside the viewfinder, with (+) pluses indicating overexposed, and (-) minuses underexposed. The goal with these is to adjust your shutter speed and aperture, even the amount of light if possible, in order to get the exposure reading of the meter in the center for a basically-correct exposure. You may actually want to expose with the reading a mark or so on the over side.

Unless you're using a flash device that's specifically designed to work with the TTL metering of your camera, these meters will not work in flash photography, you'll need a flash meter for that.

While these reflected-light TTL meters will get you in the ballpark, they aren't going to put the ball over the plate. You need something a little more sophisticated to get the "perfect" exposure. For this, we need to move away from the camera to a dedicated gadget.

A light meter is a handheld exposure meter for reading the exposure of ambient lighting, or non-flash photography. Although it's a rather old model, an example of a light meter can be found in Figure A.


Light meters measure ambient, or available light. (click for larger image)