Beauty and Frailties of Modern Digital Metering Systems

Virtually all modern cameras now implement reflective lighting metering system. The fact that they do makes it possible in so many ways to make better images not only in good lighting condition but also when lighting is not so conducive. Essentially this system is what measures the light and calculates what settings should be used when in all other modes but full manual.

The biggest benefactor of modern digital metering systems are the newbie photographers. These are the juvenile exponents of photography who are the future of this vocation. Thanks to built-in metering systems these photographers are capable of producing great quality images even in the most trying of circumstances.

A question that most certainly be in your mind at this point would be – “what on earth is a metering system?” The phrase ‘metering system’ sounds like it has been taken out of science fiction. No it isn’t. Metering is science but it isn’t fiction.

Back in the days of film photography there was no option to meter a scene automatically. Photographers would have to work the scene using very basic techniques. These would include tried and tested methods that would be considered as guidelines. We still use some of those guidelines today. These would be the sunny 16 rule, the f/22 rule and the inverse focal length rule. There are many such other rules like them.

These days we are much luckier. We don’t have to depend on these rules alone. We have digital meters in our cameras to take care of the dirty work. But even then some of the rules are quite handy when you are not absolutely sure that the built in metering system has got it absolutely right.

So what is about metering manually that seems to freak out photographers? Even the professional ones that is? To understand we need to know how modern digital meters operate, understand how they can accurately meter in certain situations and at other times get things horribly wrong.

You see digital meters are designed so that they can give you an average estimate of the reflectance of a scene and accordingly help you dial in the right exposure values. By this time you must have understood that the right exposure values are a combination of shutter speed and aperture value.


Digital meters are driven by the reflectance of a scene. Reflectance means how much light is reflected off of a scene. This you would agree depends on the colors. If a color is bright it would reflect more than if were darker. A scene which is predominantly white, in that sense will be at the extreme end of the reflectance scale, reflecting all of the light falling on it.

On the other hand a scene with predominantly black colors, will absorb much of the light and reflect none. In the first case, if you are in the aperture priority mode, the digital meter will automatically give you a faster shutter speed so that the lens does not remain open for a long period of time. It sees the scene to be too bright anyways and so a longer shutter speed risks blowing out an image.


If you are in the shutter priority mode the camera will automatically select a smaller aperture to allow less light in for the same reasons. In the second case, you get a slower shutter speed and wider aperture in aperture priority and shutter priority modes respectively.

Did you notice something unusual in the previous four paragraphs? I bet you didn’t. Before you hurriedly try to skim through the paragraphs again let me tell you something. This whole business of reflected light metering isn’t something that is perfect for metering all types of scenes. This system has a basic flaw. It is dependent on the reflectance of a scene. In the reflected mode when the scene has too many bright colors the camera will automatically under-expose. If the scene has too many dark colors it will automatically over-expose.

This is why photographers, especially those who have shot their entire life with film cameras and without the aid of a built-in light meter still use a hand-held light meter. This is because hand – held light meters don’t depend on the light reflected off of a scene in order to assess the right exposure values. Instead, it measures the incident light that falls on a scene. This is why these light meters are accurate in giving the perfect exposure values regardless of the distribution of colors in a scene.

So, we come back to the question of why metering manually for a scene is such a big challenge. When we meter manually we disregard what the camera says. With a built-in light meter it takes a good understanding of exposure values and also a lot of confidence to tell the camera whether to over or under expose a scene.

But the hand-held light meters gives us an edge. These light meters only measure incident light and thus the reflectance of the scene is not something that would sway their assessment of the correct exposure value. All you need to do is set the aperture value you want on your camera, dial the same on the light meter and then take a reading. The light meter will tell you what shutter speed you need for an accurate exposure.

Does it mean that for all possible reasons the built-in light meter is an unnecessary feature on your camera? No I wouldn’t go that distance to label it as unnecessary. The built-in light meter is still an effective tool in the right hands.

For example when you are shooting with the spot metering mode it still gives you the option to sample a small percentage of the frame in order to accurately meter a scene. The spot metering mode is often used by photographers when they want to sample a middle-grey subject from a scene. This allows them to get a reference point and then accordingly balance the exposure. You can read up more about different metering modes in our Camera Metering Modes Explained article.

Then again the matrix metering mode is an excellent example of technical ingenuity. Nikon 3D Color Matrix Metering System II, for example, uses an actual database comprising of more than 30,000 images to refer to when metering for a scene and uses all that information to correctly set the exposure values. Matrix metering is generally used for landscape photography.

If you have enjoyed this post and wish to receive updates about any future content subscribe, like and follow us!
This entry was posted by Rajib Mukherjee.

Leave a Reply

Your email address will not be published. Required fields are marked *