Learn to Measure and Distribute Light Correctly

To "photograph" literally means "drawing with light". The strength of light, the type of light, and the direction of the light, the way these parameters interact with your subject is decisive for the outcome of the finished photo. Light metering is the measuring of the amount of light passing through the lens onto the sensor of your dSLR. For this task the camera is equipped with a light meter that passes on information to you and to other parts of the camera with the help of a tiny computer. The more precise the metering the better exposure the photographer will get.
  

In order to get a good exposure (= a photo that is exposed well / has good light) it is necessary for the camera to measure the light falling on the subject with great precision. Metering is an automatic process that takes place before the shutter is fully depressed. In some cases you, however, need to give your camera a helping hand.
 
Metering Correctly
In order to understand the process of metering you need to understand the following tools: shutter speed, aperture, and ISO values. We suggest you read about these tools before continuing. If you have chosen the aperture priority mode (A or AV) and you have chosen a specific aperture, e.g. f/5.6 and a specific ISO value, e.g. 200, the metering of the camera will decide the resultant shutter speed. The more light available the faster shutter speeds, less light available means slower shutter speeds. Regardless of the specific shutter speed your camera calculates, what is important to know is that this shutter speed is the result of the metering.
 

The Norwegian Defence Research Establishment during an assignment on the Vestfjord near the Lofoten Islands. The camera has been tricked by a relatively dark sky and the dark surface of the ocean and has consequently allowed too much light in the photo which has been overexposed (too light).

 

For this photo the photographer has taken control of the light measurement in accordance with the theories presented on this page. The result is a correctly exposed subject with improved colours and a much better mood.
 
When you start out as a photographer you want to get the photos that other photographers get: photos with beautiful light, pretty colours, good dynamics, and an interesting use of light. Despite the fact that modern digital cameras have become very good at measuring light they do unfortunately not always succeed at first try. Photos simply turn out differently than you had imagined they would. They may turn out too dark, too light, with too much contrast or with colours that are much too dull. When you do not succeed the problem is almost always that, being an inexperienced photographer, you have insufficient knowledge about metering
 
Different Ways of Metering Light
A modern single lens reflex camera uses something called reflected-light metering.
 The light metering unit is placed inside the camera and the unit bases its measurement on light reflected by the subject. There are many other types of light metering. Such as, for instance, the hand held incident light meter. Reflected-light metering is, however, used for 99 % of all exposures today and this is the kind that we will focus on.

 

Back in the old days, using the so-called reflected-light meters was the best way of getting a good result. Nowadays, the built in light meter of the camera is so accurate that you can use it for 99 % of all photos. There are, however, still photographers who choose to use light meters like the two models depicted above because they want to be 100 % in control.

 

Find your camera manual and look up light metering. The manual will inform you about what kinds of metering you can choose from and where the metering control is located.

  

Mercantour, France. The light meter of your camera will have no problem figuring out evenly lighted subjects such as this. In most cases you can simply select the standard metering mode: light is measured in the entire scene or in most of the scene.

 

Basically, (standard metering mode, evaluative metering mode) light is measured in the entire scene or in most of the scene. Depending on the mode you have selected (A, S or P) shutter speeds and aperture are adjusted in accordance with an average of the entire photo. In most cases this process will be sufficient. You may, however, experience some problems if a small part of the image is significantly brighter than the rest of the photo or if you want a part of the photo to be very bright or completely black.

 

Tongariro NP, New Zealand. For this shot we used centre-weighted metering giving priority to the most bright parts of the landscape. Put differently, the photographer asked the camera to ignore the very dark area in the left side of the scene. Using standard metering would have resulted in an overexposed image.

 
Centre-weighted metering focuses on a smaller part of the subject than standard metering. This type of metering opens up new vistas for creative use when used in connection with, for instance, landscape photography in bright sunlight. See the above example. 

 

The Illulisat Icefiord, Greenland. For this shot spot metering was used. The actual metering was done focusing on the very bright sky. Had we, instead, used standard metering the photo would have turned out much less colourful.
 
Spot metering is performed using only a tiny part of the scene. The camera uses the input from just the precise spot that the photographer chooses. You can use spot metering for shooting silhouette photos, portraits or really well-exposed sunsets.
 
When to Use What Method?
It is difficult to give any general advice on what light metering technique will be best suited to your needs, as this depends on the available light in the location you are shooting. Generally speaking, practice makes perfect.  Try out different metering techniques in many different lights to find out what works for you. The standard metering mode works well when all of the subject is more or less evenly lighted. Spot metering and centre-weighted metering generally provide the best results in situations where the subject has very bright areas. Such as, for instance, a white object placed in dark surroundings or an object with a metallic surface reflecting a direct source of light.
 

Container cleaning, Europoort, Rotterdam. It is important that the photographer has an understanding of light metering that enables him to help his camera interpret light when shooting in difficult circumstances. For this photo we used spot metering giving priority to the daylight outside the container.

 
The Limitations of Your Camera

Even if you practice a lot and become skilled at light metering, you can still find yourself shooting in light that is impossible to render effectively. The human eye is far more advanced than the camera and it is able to determine details in difficult circumstances such as, for instance, strong backlight. The example below depicts a situation that is impossible to render for the camera regardless of the type of light metering you choose. These photos were even shot with a camera housing priced at $ 8000, this simply goes to show that even the most expensive camera housings have their limitations.

 

The Wadi el Gemal desert, Egypt. When metering for this shot the powerful desert sun was adjusted for. Consequently, the desert sand appears much too dark (underexposed).

 

The subject is the same, this time the photographer has, however, given priority to lighting the sand correctly. The result is that the sky is overexposed and that the colours have become very dull. This is, in other words, a situation where the camera is unable to reproduce what the human eye can see.

 
Exposure Compensation
You will often find yourself shooting in a situation where making small adjustments in the values suggested by the camera light meter will improve your results. You might, for instance, want your photo to be somewhat brighter than it would be if you went along with the values supplied by the camera. Or you might want your photo to be slightly darker? These approaches are called intended overexposure and intended underexposure or, in one word, exposure compensation. 

 

This is an example of how the camera light meter can be tricked by a relatively dark background.  The consequence is that the photo becomes slightly overexposed reducing colour saturation (colours will appear rather flat and dull).

 

A few seconds later the girl gives her buddy a friendly pat on the behind. A great subject and a funny story, there is, however, no time for metering light differently. Speedy exposure compensation saves the shot - and the colours even look good.

 

The term “exposure compensation” is rather lengthy, and it all sounds very technical and complicated, the principle is however quite simple. Your camera is equipped with a button or a wheel that controls this function. Check your manual to find out the exact location and how it is used. This function allows you to overexpose or underexpose your photo. You usually adjust exposure in steps of one third of an f-stop, this is a very quick way to get photos that are significantly different from what you would get by simply using the camera metering. You should however note that exposure compensation cannot be used if you have chosen the M (fully manual) mode.

 

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