Metering is the measurement of light in the scene that will give you the correct exposure. Previously, I discussed exposure compensation, and how making an adjustment with this affected the brightness or darkness of your photograph. With metering, you are going to learn how to meter for your subject for a more perfect exposure.
Sorry to say, the in-camera light meters in your DSLR can be fooled resulting in an incorrect exposure. Read on.
Metering light is measured two ways, by Reflective and Incident light. When the meter suggests a correct exposure it will be aligned at 0.
This is how your DSLR measures light. The light source on your subject is reflected back to your camera’s metering system through the lens (TTL).
Most times this type of metering is accurate. Times when it has more difficulty are:
- Back-lit Subjects: a person in front of a sunset
- Dark photographs: a black cat in shadow
- Bright backgrounds: front lit subject in the midday sun
- Light Subjects: Snow, white birds
To evaluate your exposure I strongly recommend understanding and reviewing your histogram after the first shot. I’ve written a short article to help you use the histogram.
Types of In-Camera Meters
Matrix and Evaluative metering is usually the default on many DSLRs and it’s the one I use the majority of the time, with a few exceptions.
Matrix (Nikon) Evaluative(Canon)
This type of metering creates lightness and darkness zones in the image depending on where your focus point is. After evaluating the entire image it will mark where you focused at and make this more important than the other zones.
In the Center-Weighted Metering Mode, the camera does not evaluate the entire frame, but just the middle leaving out the corners. It is also not based on where your focus point is, just the middle of the frame.
This is useful for head-shots, or a portrait that is being back-lit as it is only metering in the middle. The background elements will be overexposed.
I use this metering mode for my bird photography, small subjects with a bright background and my moon photography.
Spot metering uses a single focus point/cell to meter on. Where you place your focus point it will meter just in that tiny area. If you tried bird photography with matrix/evaluative or center-weighted (unless the bird filled most of the frame), you likely ended up with an underexposed bird or silhouette.
Partial Metering – Canon
Partial and spot metering modes work similarly.
On a Canon, partial metering takes the exposure from approximately 6.5% of the viewfinder area, whereas for spot metering the brightness is measured using just 2.5% of the viewfinder area.
On Nikon cameras, spot metering takes the exposure from approximately 5% of the scene depending on the model. This makes partial metering on a Canon and spot imaging on a Nikon very similar.
As they are both similar, consider using partial metering the same as you would for bird photography. Experiment and see which mode you prefer.
18% Gray Card
Another type of reflective metering is with an 18% gray card. 18% gray represent the middle, neutral color. Looking at your histogram black would be on the left edge, neutral (18% gray) in the middle, and white to the right edge.
To use a grey card:
- Have the subject hold it close to their face or place it in the area you will be focusing on. If your subject is in shadow the card needs to be in shadow as well.
- Fill the frame of your camera with the gray card, either by stepping closing or by zooming in.
- Make sure the card is not tilted but flat up to the lens.
- Now, make your adjustments to the desired aperture, shutter speed, and ISO until the meter reads at zero.
- Remove the gray card and shoot away.
Larger 18% gray panels are available, like this one. Find one that suits your needs.
Incident Light Metering
Incident light is the light that falls on the subject and is measured with a handheld light meter. It is not affected by the brightness or tone of the subject you are metering on and is much more accurate.
This type of meter is held near the subject and the light is measured. First, you dial in the ISO you are going to use Hold the meter near your subject. When measured you are given the speed and aperture for correct exposure.
You do not have to use that recommended shutter speed or aperture. Instead, let’s say you wanted to open the aperture from the recommend f/5.6 to f/8 for more depth of field. That is one full stop.
Recall by stopping down the light by 1 Stop will reduce the light by half. To recover the loss of light we need to slow our shutter speed by 1 Stop, to allow more time for the light to enter.
You can review this by reading my article about Manual Mode.
**Although the incident light meter is more accurate it is more often used for some types of photography, like portraits, and studio work for very precise light metering.
I’ve discussed the two types of metering, in-camera meters, the 18% gray and a general overview of hand-held light meters.
At this point you are becoming a master of your camera. Continue to follow my new blog post to stay up to date and add to that new fund of camera knowledge you have.
Assignment (if you choose)
Use two metering modes. Use Matrix or Evaluative to take a photograph of any subject you like. Second, use the spot metering mode and take a photograph of a bird, or small object you want to be exposed properly. Try the same subject with different metering modes and compare them.
As always, have fun and keep shooting!