With light meters being added to almost all cameras in production, the hand-held meter has been forgotten to a great degree. There are however still plenty of uses for a hand-held meter even with such good meters in the cameras.

Categories of meters-
Ambient light
Ambient & Flash
Spot Meters
Incident Meter/ Reflective
Ambient meters read only constant light and will not respond to light from a flash. Most of the meters on the market in this category are primarily reflective metering. Reflective metering can be a wide-angle of coverage and the meter takes into account all of the various densities within the field. A reflective meter is calibrated to read 18% gray. If you are metering an object with very white or very dark areas, the meter will not be totally accurate. For the best accuracy with a reflective reading, you ideally should use an 18% gray card in the light that you are shooting and meter off of the card. Without a card, there are a couple of tricks that can be used to get a more accurate reading. Outdoors, you can meter off of trees or grass. The gray density on these is approximately 18% gray. Another trick to use is to meter off of the palm of your hand and take off 1 stop (if the meter reads f8 you set to f11).
An ambient meter can also be primarily an incident meter. This type of meter is used by pointing the meter toward the camera from the area that you are shooting. The meter gathers the light and gives a reading that is correct. This type of meter was used and still is used by motion picture studios. They sometimes are referred to as a “studio” meter. The sensor is a white globe, and is usually much larger than a primary reflective meter. Both types will work, either incident or reflective, but they are usually better at one type or another. For example, the Sekonic L398 meter is primarily an incident meter that will do reflective, and a Sekonic L308S or L358 is primarily a reflective meter, with incident available.
Flash meters read light from electronic flash. These are incident light meters. They are used at the subject point, and aimed at the camera. When the flash is tripped, the proper f-stop will be shown. High-end flash meters, such as the Minolta Flash Meter, read in very precise measurements. Some of these types can collect various readings and you can determine an average exposure.
Ambient & Flash meters can do both types of metering. The flash metering is not as precise as a dedicated flash meter, but the readings are still very good. This type of meter is currently the most common one.
Color meters have become the least valuable in today’s digital world. With computer manipulation available, a photo that is off-color can usually be fixed in the computer. If you are using transparency film, a color meter is used to identify the exact filtration needed for correct color.
A spot meter is a reflective meter that can identify the exposure within a very small visible area, which can be as small a one degree. These are very useful when you are not able to get close to the subject. With this type of meter, you select from areas that you know will produce a result the same as 18% gray. Some meters in the Gossen line had an option of adding spot metering to a normal meter. These were in the Luna Pro line.
Cell types and power sources:
Older meters and a few of the newer ones use a light sensitive cell that requires no battery. The most common is the Sekonic L398A.
Meters that require batteries are various types such as CDS, (cadmium sulfite), Silcon Blue, Gallium and others. The oldest type, and not used in new meters at all, is the CDS. The CDS meter retained light and could not be moved from situation to situation without the metering needing to “rest” to eliminate any bright reading. The newer meters in cameras and in hand-held meters have cells that do not retain light. Battery type can be AA or button batteries depending on the model and brand.
Remember this – The correct exposure is always the best whether you are shooting digital or film. You can only adjust an image so much. If a picture is seriously under or over exposed, no amount of manipulation can totally fix it.
~ Ed Warrick