Spotmeters

A spotmeter is a reflective light meter that measures how much light is reflected (or emitted) from an object. This is very similar to an on-camera exposure meter. However, a spotmeter measures a very well defined and small angular cone, often down to one degree. And, a spotmeter most likely is more accurate and sensitive than on-camera sensors.

Because of the use of TTL (through-the-lens) metering, a spotmeter requires a bit of optics. Consequently, spotmeters are a bit more expensive than incident meters. Expect to pay about US$400 for a decent spot-capable meter.

Spotmeters are very useful if you want to control the exposure of various portions of a frame. For example, if you want to capture the highlight and shadow details of a tree, partly in the sun, you want to measure the lit side, and measure the shadow side. If the two exposure values are too different, then you need to decide which side to sacrifice.

Sure, you can do the same by walking up to the tree, measure one side, then measure the other side using an incident meter. However, if the tree is not accessible, then you cannot use an incident meter for this purpose anymore! For the same reason, a spotmeter is very helpful if you want to know the exposure value of the white top of a mountain in the background.