The digital SLR camera’s metering system is a complex process which involves evaluation of the reflected light in a scene and then assessing the correct exposure value to make a well-exposed photo. Metering modes such as Matrix or Evaluative metering works fairly well in even lighting conditions. In an even lighting conditions these metering modes can correctly assess the amount of light in a scene and determines the right aperture and shutter speed, leading to a proper exposure. However, when the lighting changes or there are more than one light sources or there are different zones of brightness and shadow things start to get complicated for the camera’s built-in metering system.
In a scene which has both shadows and brightness the camera will try to even out the exposure so that it can retain as much detail as possible from both the shadow areas and the highlights. In technical words the built-in metering system will try to make everything 18% grey. This ‘averaging’ of exposure is the reason why sometimes you get perfectly exposed pictures whereas in other situations the picture is either washed out or is under-exposed. Learn more about exposure settings and how to set the correct exposure in this online tutorial.
Different camera manufacturers uses different names to refer to their metering modes. Regardless of the names assigned, here is a list of the usual metering modes on a camera.
Unless you have tinkered with the metering settings of your DSLR, chances are that you are using the default mode which is Matrix Metering. This is the default metering mode set by the camera manufactures on their DSLRs as it is the safest and the most accurate metering system when you don’t know what you are doing.
In this mode the camera divides the entire frame into a number of zones. Each of these zones are then evaluated for the purpose of calculating the amount of shadow and highlights, as well as color, measurement of the distance from the camera and a few other aspects. Depending on the analysis of this information the camera then selects the right exposure value (aperture & shutter speed) to achieve a correct exposure for the scene. Matrix metering also takes into account the AF point(s) that is (are) currently active, giving it greater importance that any other point on the frame.
Matrix metering is the name used by Nikon to refer to the metering system in their cameras. It is the same thing as Evaluative Metering used by Canon to describe the complex metering system in their DSLRs.
Matrix metering system is the preferred mode for shooting in such conditions where a scene is improperly lit-up or if there are multiple zones of highlights and shadows including no specific zone / subject which demands priority. One possible genre of photography that you can shoot using Matrix metering is landscapes. Having said that you could also Matrix metering for cityscapes and in most wide-angle shooting requirements.
Matrix Metering can sometimes be frustratingly difficult to produce good results with. At other times, still, it seems like it can read your mind and produce fantastic results. This is because Matrix / Evaluative metering is not designed to be the perfect metering mode in all possible shooting situations. It is more of a generalised metering mode where the average brightness across the whole scene has to be considered for assessing the correct exposure value.
Spot metering is suitable when a large part of the scene has highlights blown out and you need to expose for the subject which is comparatively in a darker zone and or is at the center of the frame. This mode is also suitable when you need to highlight a face which occupies a very small part of the frame. Spot metering is ideal for all the above situations and evaluates the reflected light and color for a small spot of the frame, which is usually the area that is immediately around the active focusing point. Spot metering is also suitable for backlighting situations as is Center-weighted metering mode.
Center Weighted Metering
Center-weighted metering mode, as the name suggests, gives preferences to the center zone of the frame. This is a go between Matrix / Evaluative metering and Spot metering and uses more than the area that the later uses to correctly meter a scene. However, in this case, just as in spot metering, a larger importance is placed on the active focusing point.
Center-weighted metering mode is suitable in situations where you have a one or more people standing for a shot and together they occupy a somewhat larger area than what can be covered by Spot Metering. Center-weighted metering is also suitable for backlighting situations where the subject may be standing back against a window or outdoors directly in front of the sun. If you use Evaluative / Matrix metering you are only going to get a silhouette of the person and no noticeable detail.
Working With the Metering Modes
Due to the relative complexity that is associated with the use of exposure metering, camera manufacturers have come up with more than one modes. This is under the notion that at least one of them will be suitable under a given condition. In most of the cases either Matrix / Evaluative, Spot or Center-Weighted metering mode is applicable, but in some cases it becomes necessary to override what the camera thinks is right and what you know is correct.
One such situation is when a given scene has a lot of white color in it. Let’s say you are trying to photograph a snow scene. The camera sees all that white color and decides that the scene is way too bright to be properly exposed. Now, every digital camera sensor is designed to make a scene 18% grey. It is a middle tone that averages out the highlights and shadows in a scene. In the above example the over-abundance of the white color in the scene means the camera will try to meter it and then under-expose it so that the scene is ‘greyer’. The result will be a darker picture. This is a classic example when the camera’s metering system can get it awfully wrong. In this situation you will need to use the Exposure Compensation button and use 1 or even 2 stops of positive exposure bias in order to get the exposure correct.
In another example, let’s say a model is standing against a black wall wearing a black dress. In this situation the camera will see there is huge quantity of black tone in the scene. The face of the model which covers only a tiny fraction of the whole scene is not going to convince the camera that the scene has any sufficient highlights. Thus the camera will meter the scene and try to over-expose, making the subject’s face too white / washed out. Thus in this condition, you will need to use negative exposure compensation by 1 or even 2 stops to get the right exposure.
What is Exposure Compensation?
Exposure Compensation is an adjustment of the exposure values as suggested by the camera. Most cameras allow you to adjust the exposure values in P (Programmed-Auto), A (Aperture Priority) and S (Shutter Priority) modes. It is possible to adjust up to two whole stops of compensation in either direction in most DSLR cameras. In some semi-professional and professional DSLRs it is possible to adjust exposure compensation by more than 3 stops. Please note that exposure compensation can be adjusted in full 1 stops, 2/3rd of a stop and 1/3rd of a stop in most DSLRs.
The exact process of adjustment differs from camera to camera and from brand to brand but usually it involves pressing the Exposure Compensation button (denoted by the markings +/-) and then rotating a dial. Please note that in aperture priority mode rotating the dial changes shutter speed and in shutter priority it changes the aperture value. If used in programmed auto mode it will change both aperture and shutter speed values. This tutorial explains in further detail the relationship between Shutter speed and Aperture.
The final straw in your hand, when everything else seems to have failed is to use the manual shooting mode and use the metering indicator just as a guideline. In Nikon cameras manual mode does not allow you to use exposure compensation. However it will still show you the exposure meter, working pretty much like a light meter in this mode.
When you look through the viewfinder you will notice the meter readouts and a marker (like that in a thermometer). If your exposure if off, either too bright or too dark, the meter is going to slide to the left or right. You will need to change either the shutter speed or the aperture value (depending on your preference) and balance the exposure. The reason why you are using the manual mode is so that you can manually set the exposure value and have creative control over your photos. Thus, you can use whatever values you need based on the desired results. Learn more about manual exposure in this tutorial.