The Light Meter

I have owned a Sekonic L-300 light meter for decades. I now have two more external light meters including a better Sekonic meter (L-358) and a (Lunasix 3). Plus every camera I currently own including two old film cameras (Nikkormat and FM2) and my Olympus OM-1 and OM-5 all have light meters built in.

Why not just use the built-in meters on the cameras? While super convenient and included in the camera the built-in light meters are what’s called a reflected light meter. In other words this built-in light meter reads the light that is being reflected from the subject and seen through the lens as it hits the sensor.

On many a modern camera this reflected light meter can be configured to read everything at once or a selected portion of the scene or even just a tiny spot. (In the old days a spot meter was an expensive and highly coveted device.)

Internal light meters are usually activated by holding the shutter button half way down and can lock in an exposure while the photographer re-composes the image. This is helpful when shooting images under changing or contrasting lighting situations.

So again the question come up: why use an external meter?

Reflective meters in cameras can be easily fooled by challenging lighting. Remember our black and white cats against contrasting backgrounds. While in the hands of a competent photographer using the reflective light meter in spot metering mode it can be done but by using an external light meter in what’s called incident light meter mode it’s a lot easier and more accurate.

Incident light meters have a dome (as seen above) that represents the image being photographed. The photographer takes an incident light meter reading by walking into the scene (or person for that matter) being photographed and points the light meter dome back toward the camera position.

The meter measures the light falling on the dome which is designed to represent a gray card which is actually what it sounds like. This $10 accessory is a card that has a middle gray colour that is what’s called 18% gray,

This 18% gray is what your camera’s meter is using when it calculates the correct exposure for a scene. If you were to put a gray card in front of your camera where the light falling on it was the same as the light falling on your scene itself you’d get a proper light meter reading regardless of the contrast of the scene itself (again remember our cats).

The easiest way to demonstrate the use of a gray card is to take your camera outside during a snowstorm and take a photo. The exposure of the snow as measured by the internal reflective light meter will set the exposure and the snow will appear to it as 18% gray which will be reproduced looking dull and ugly.

Using a gray card as your target with your built-in meter will result in a snow scene that’s bright white. You can do the same thing by by opening up (allowing more light) the lens by two stops (a stop is a unit that describes the change or difference between exposure values. You’ll hear photographers talk about adding one or two stops to their exposure.) and again the snow will be reproduces as white and not gray.

Now for the kicker!

An incident light meter’s dome replaces the 18% gray card and results in more accurate exposure control. Besides walking around using an incident light meter makes you look cool LOL.