Working In Multi-segment Metering Mode

Right Image: Minolta Maxxum 9, Tokina 80-200mm f-2.8 ATX lens, Fuji Velvia, Bogen tripod and ball head.
Multi-segment metering, aperture priority, 1/30 sec at f-11. Autofocus.

Multi-segment metering also called evaluative metering,  is the standard metering system built into most cameras made today. It wasn't long ago when centerweighted metering was the standard metering, plus spot metering for times when you needed to meter only a small portion of the scene. Centerweighted metering reads the light reflected from the subject with attention given to the center of the frame. Spot meters work the same way, except you can get a reading from very small part of the scene, around 2 to 5 percent of the area. In either of these two modes, meters want to make everything a medium tone or 18% gray. If your subject is medium tone, you don't need to make any adjustments. Otherwise you need to open up for light and close down for dark subjects. You simply add or reduce 1/3, 1/2, 1, or 2 stops of light depending on how light or dark you want the results to be. You can do this in manual exposure mode or use exposure compensation dial in auto exposure modes. (See Exposure for more detail).

Multi-segment metering is also reflected type, except the meter divides the frame into several areas and calculates exposure based on these readings.


Multi-segment metering with several areas which divide the scene for more precise light measurement.


The problem is that you have no idea how your meter calculated each area. How many stops of light was reduced for the dark upper left portion of the frame? how many stops were added for the light lower portion? What about all the other tonalities in between? We don't know. If you add or subtract from multi-segment metering reading as you would with centerweighted and spot metering, results can be unpredictable and usually unacceptable.

For example, you can spot meter a light red object and simply add 1 stop of light to make the object light red. Do the same with multi-segment metering, and you get the same result only if the light red object fills the whole frame otherwise you will affect all other tonalities in the frame including the light red portion. Again, you don't know how the multi-segment metering calculated the areas and how much light it added for the light red portion if any.

We know if one tonality is calculated correctly, all others fall into place. Meter a light red area and add 1 stop of light, and dark red area in the same scene will record as dark red, medium red records as medium red, and all other colors as they are. Multi-segment metering gives an exposure based on reading of the light red, dark red, medium red, and other tonalities in the scene. We don't know how much to compensate or if we should trust the multi-segment reading.

It took me a while to learn how to work with multi-segment metering when they were introduced several years ago. Compare the multi-segment exposure reading with that of spot or centerweighted. If the difference is 1 stop, make no adjustments. Most of the time the multi-segment reading gives good results. Anything under or over one stop may require compensation. In this case, switch to spot or centerweighted and add or subtract light.   My advice is not to make any exposure adjustments in multi-segment metering mode unless the whole scene is of the same tonality and you want to make it lighter or darker than they appear.

Recommended reading: Understanding Exposure: How to Shoot Great Photographs with a Film or Digital Camera Synopsis More than 100 vivid, graphic comparison pictures illustrate every point in this classic and can help any photographer maximize the creative impact of his or her exposure decisions. Peterson stresses the importance of metering the subject for a starting exposure and then explains how to use various exposure meters and different kinds of lighting. The book contains lessons on each element of the triangle and how it relates to the other two in terms of depth of field, freezing and blurring action, and shooting in low light or at night. A section on special techniques explores such options as deliberate under-and over-exposures, how to produce double exposures, bracketing, shooting the moon, and the use of filters. Understanding Exposure demonstrates that there are always creative choices about how to expose a picture - and that the decision is up to the photographer, not the camera.