No matter how smart your camera’s built-in light meter, it will sometimes under- or over-expose. You can learn to compensate for such errors, but there’s a more accurate and reliable method – using a hand held light meter, such as the Sekonic L-308S hand held light meter shown here.
When using your DSLR’s internal light meter you’re measuring the light reflected from the subject, and the camera assumes that the tones in the scene will average out to a mid-grey. This is fine for most subjects, but when the subject is mainly white or black, the meter will set an exposure to record this as grey. So with white subjects you’ll end up with an under-exposed shot, and with black subjects you’ll end up with an over-exposed shot.
Hand-held light meters avoid these headaches by measuring the light falling onto the subject. Known as an incident reading, this is a much more accurate way of measuring exposure because it isn’t affected by the colour or tone of the subject. Take a meter reading from the subject position rather than where you’re shooting from, and point the meter back towards the camera. This technique is ideal for portraits and still life.
How to use a hand held light meter for perfect exposures
Step 1: Select metering mode
Most meters measure flash as well as ambient light, so pick the right mode – in this case ambient, usually indicated by a sun symbol. You also need to set the ISO to correspond with the ISO choice on your camera.
Step 2: Set up for incident light
To measure the light falling on the subject, ensure the white dome is covering the light-sensitive cell. Put the meter by the subject, and check that the white dome is pointing towards where your lens will be.
Step 3: Take the reading
Now press the button on the side of the meter to measure the light falling on the subject. You can then scroll through the combination of shutter speeds and apertures that correspond to this reading by using the meter’s up and down buttons.
Step 4: Transfer the reading
Choice of settings is down to whether you need a particular shutter speed or aperture for depth of field. With your camera on manual exposure mode (M), simply enter the shutter speed and aperture from the readout of the meter.