It's important to know just how your digital camera light meter works if you want properly exposed images. The metering system more or less controls the camera's aperture and shutter speed settings and it does this based on the ISO speed and the image's lighting conditions. The metering usually includes spot, evaluative zone or matrix, partial, and centre-weighted metering. All of these have lighting conditions that they excel at as well as those they fail at. It will help your end results if you understand these options.
Incident and reflected light
All light
meters in cameras are a little flawed from the start since reflected light is
the only type they can measure. This means the camera has to guess how much
actual light is shining on your subject. If each object reflected the exact
same amount of incident light it wouldn't pose a problem. However, all objects
reflect different amounts of light. Due to this, camera light meters are
standardized and they base their metering on how much light a middle grey
object would reflect. When the camera is pointed at something that's lighter or
darker than this shade of grey the meter can't properly calculate how much
light is being reflected and this will result in images that are over or
underexposed.
Middle grey
is typically an 18 per cent reflection of incident light, but most cameras
figure it out to be anywhere between 10 and 18 percent. If the object in the
image reflects less or more light then the exposure will likely be off.
However, even if the photo has dark and light objects in it, the average amount
of reflected light could fall into the camera's middle grey range. If your
image is of a black cat sitting on a black rug or a white object in the snow
then you may have a problem getting the correct exposure.
Metering options
If you
want properly exposed shots for a wide range of reflectance and lighting
options you can try and meter different areas of the scene. The whitest parts
of a scene are used the most for exposure calculation while black sections are
basically ignored. The best way to meter the image is to calculate the
reflected light for each part of the photo. This means the scene is divided
into sections and you can calculate the amount of light for each of them.
Partial and spot metering
These
types of metering will allow you to control the exposure since you can select
the part of the image you want to meter. However, it takes a bit of practice to
get used to them. With partial metering, it would be useful when taking a shot
of somebody who is backlit. If you meter off of their face it will make sure
they person doesn't turn out underexposed in front of a bright background as
this would make them appear to be a silhouette. If the person's skin shade is a
long way from middle grey though, it might not be perfect. Spot metering is
mainly used when you need to meter a small or specific area of a scene.
Centre-weighted metering and exposure compensation
Centre-weighted
metering used to be quite common as a camera's default setting. But these days,
matrix and evaluative are more common, especially partial and spot metering. Centre-weighted
metering will produce predictable results while evaluative and matrix modes use
complicated algorithms that are more difficult to predict.
You can
use exposure compensation with any light metering mode. This will allow you to
change the settings if your photos are consistently under or overexposed. For
instance, the white object in the snow as mentioned above would result in an
underexposed shot unless you manually adjusted the exposure compensation to
plus 1.
By: Stephen Hockman
Article Source: http://EzineArticles.com/7559297