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In-Camera vs. Handheld Light Meters
by Chuck McKern

We have all grown accustomed to the convenience of having a light meter built in to the camera. They have always done a pretty good job and as the years and technology have moved on, these on-board meters have become much more accurate. With that in mind, is there still a reason to have a handheld meter? To honestly answer this question we have to take a close look at how the in-camera meters work.

All modern cameras have a built in meter

The primary metering type for most cameras today is an overall meter. Meaning, it will take readings from different parts of the scene to cover most, if not all, of the viewfinder. These types of meters have different names depending the manufacturer (Matrix, Honeycomb, Evaluative). Although all the manufacturers have a different approach to how they take their readings, the fundamentals behind them are the same.  To provide an accurate overall exposure for a scene, the camera's meter looks at the brightness level of multiple areas of the picture and determines the correct exposure based on what it sees. This technique is pretty good for average pictures. When you get into areas where the light is restricted from reaching large areas of the scene, it can cause false or inaccurate readings. 

Let's say for example, you're shooting a play on a theater stage. The backgrounds are usually very dark and the subjects are being lit with bright stage lights. Most meters will see the dominate area of the scene as being dark (backgrounds are usually dominant unless you can get in close using a zoom lens).  The meter will want to brighten that dark area up by calling for more exposure. This, in turn, will cause your subjects to become over-exposed and possibly blurred if the shutter speed dips too low.

For times like this, higher end cameras (as well as a few point-and-shoot models) have a spot meter feature. This spot meter will allow you to tell the camera to ignore the background readings and worry only about what is in the center circle (bracket in some cameras) of the viewfinder. 

In the scenario described above, the camera will ignore the background and will meter for just your subject (assuming you keep your subject in the appropriate markings in the viewfinder). But if you are off in centering your subject, the meter will expose for whatever it sees. So watch out!

Center weighted meters are still around in most SLRs as a third option. This type of meter comes in handy for a couple of reasons. First, if you are moving up from an older manual camera to one of these newer sophisticated machines, chances are you have been using a center weighted meter and know exactly what it's short comings are. Having a center-weighted option will allow you to use your new camera right away while getting the results that you are accustomed to getting - allowing you to learn the camera's other meters at your leisure. 

The second reason for the center-weighted meter is a technical need. For shooting a scene where the light level is distinctly different on your subject than on your background, but your background still has some importance, you would use this option. 

Most cameras have a large circle in the viewfinder.  When using center weighted metering, the inner part of the circle will make up a majority of your exposure and the remainder, outside the circle, will make up a smaller part of the exposure. The amount of weight given to the center portion will vary depending on the make and model of your camera. The most common combinations range from 65%/35% to 75%/25%, the larger number being percentage of weight given to the inner circle.

All of these styles of metering are accurate when used effectively. So why would we need anything else? The problem with in-camera meters is that they are calibrated to 18% gray. To understand what this means, lets look at an extreme situation. If you were shooting a high key (white on white) or a low key (black on black) image, your in-camera meter would not give you a correct reading. It will want to make everything 18% gray. Your whites will become blown out (over exposed) and your blacks will be muddy. If you were to include an 18% gray card in your scene and set your camera based on the reading you get from it, you would then get the correct exposure. With out it, your exposure would be several stops off. 

One last area of concern with the in-camera meters is that they meter the light being reflected by your subject, not the light falling on it. This is usually not a problem unless your subject is highly reflective. Highly reflective objects can throw off camera meters causing them to over expose. 

Gossen reflective meter

This brings us to the handheld meter. There are two basic types of handheld meters. The first is a basic reflective meter. It works in basically the same way as your in-camera meter and measures light being reflected by your subject. Reflective meters are good with the old manual cameras that work great but their internal meter quit and is not repairable. 

The next common handheld meter is the incident meter - my preferred meter. They are usually available with or without flash meter capability.  Flash meter capability is needed for use with studio strobes. An incident meter will allow you to get the most accurate reading of light on your subject. It reads the amount of light falling on your subject and cannot be fooled by reflective surfaces. It also doesn't cause a shift to 18% gray as in the examples of high and low key shots mentioned above. 

Sekonic incident meter

You could even use an incident meter in the theatre example. If you can get in during a dress rehearsal (just ask, you may be surprised by how easy it will be to get in), get a reading with the meter. Be sure to ask if they are rehearsing with the same light levels as they will use in the actual show (they probably are), and if they are, get your reading and manually set your camera.  You now will be able to shoot the same situations without having to stay concentrated on that small area in the viewfinder. 

Most handheld meters can be adapted to be used as a reflective meter by changing a piece over the light sensor. In this same manner, a lot these meters can also be converted to a spot meter. 

While there are some advantages to shooting with the handheld meter, if you are well experienced with your in-camera meter, you will probably have learned what types of shots trip it up, and how to compensate for them.  Also, with the wide exposure latitude of most films today, you probably will not need a handheld meter for most situations. 

But those of us, who are sticklers to get the most accurate exposure possible, or those of us shooting with studio lighting, will still carry  handheld meters for when the need arises.

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Is there still a reason to have a handheld meter?

The problem with in-camera meters is that they are calibrated to 18% 
gray

Those of us who are sticklers or are shooting with studio lighting will still carry  handheld meters

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