Friday, June 10, 2011

Understanding In-Camera Metering

One of the most challenging things to do in photography is to transition from being an amateur to an advanced amateur or a professional. Understanding in-camera metering helps to make this transition smoother. The following information will be given with a Digital SLR in mind for the user.

In today's digital landscape, the 3 most common types of in-camera metering the user can select is: Spot, Center-weighted, and Evaluative/ Multi-zone/Matrix metering. Each metering type is available so the user can select the most appropriate one depending on the location and lighting conditions. Knowing the advantages and disadvantages of each metering type will help the user to set up your shot correctly and get the best exposure.


Spot Metering
Spot metering only takes the subject of the scene into consideration, and usually no more than 5% of the scene. Typically, spot metering is selected when your meter can be fooled by a strong back light or a very dark background. This selection enables the camera to measure a very small area of the scene. The result many times can be over-exposure or under-exposure of everything except the subject. That is why Spot metering is not used as your primary metering but only for specific exposure situations as mentioned previously. One tool to help the user be more accurate with Spot metering is to use the AEL (auto exposure lock). Locking in your reading reduces the chance of a bad exposure if you need to recompose your shot.

Center-weighted average metering
Center-weighted metering concentrates on the central part of the scene (typically 60 to 80% of the viewfinder area). Your camera will evaluate the light levels of the entire frame but will place much more weight in the center of the image. The result is that the focal point is the more ideally exposed without dramatically over-exposing or under-exposing the edges of the frame.

Multi-zone metering
Another common name for this type if metering is Matrix metering. This type of metering measures the light intensity in several zones in the scene, then combines the results to find the setting for the best exposure. The type of factors taken into consideration in multi-zone metering are: autofocus points, distance to the subject, areas in or out of focus, colors in the scene, and backlighting. Typically the multi-zone system will expose most correctly in the area of the auto focus point. The concept behind multi-zone metering is to reduce the need for manual exposure compensation.


Reading the Meter Scale:
What a metering scale in a DSLR viewfinder may look like
You typically want your scale to read 0 for a correct exposure (there are some exceptions to this). If the metering marker is on the negative side of the scale, then you are underexposing your image which means there is not enough light. If your marker is on the positive side of the scale, then you are overexposing your image which means there is too much light.
Photos above: Left- an underexposed image which would read on the negative ( -) side of the scale. Center- exposed at 0 for a correct exposure. Right- an overexposed image which would read on the positive (+) side of the scale.

 
Exposure compensation
Some cameras include a manual exposure compensation feature to adjust for less-than-optimal exposure situations. Commonly, the adjustments are available in third or half stop increments. Usually the exposure can be adjusted up to 2 or 3 stops in either the positive or negative direction.


So why is metering correctly so important? The correct exposure is always the best whether you are shooting digital or film. By underexposing or overexposing you are loosing important information and details. You can also only adjust an image so much during the editing/printing stages. If a picture is seriously under or over exposed, no amount of manipulation can totally fix it. Plus, having a good exposure to start with will also save lots of time during editing!


Miss our article on hand-held light meters? Check it out here.