Metering is one of the most important things I learnt after joining Mr. Munish Khanna’s course a couple of years ago(www.munishkhannaacademy.com). It actually came about after a disastrous assignment in which I had to do a portrait of someone in my family. After much coaxing and cajoling, my dear wife agreed to be my model. Inspired by some great images I had seen, I asked her to pose next to a window such that one part of her face was lit by the morning light streaming in, while the other part was in relative darkness. Try as I might, I never managed to get the image right. The problem was that the lit part of her face was always getting over-exposed, with all details getting burnt out. Here is what the image looked like.
First of all, my wife hates having photos taken. And on top of that, this is what I come up with. You can imagine the grief I got after taking this photograph! It was only later, once I learnt about metering, that I understood why this was happening.
Most cameras have 2 or 3 metering modes, the selection of which determines how a particular image is exposed by the camera. In the case of the image above, the camera was in the default “matrix” metering mode(called the evaluative mode in Canon cameras). In this mode the camera averages out the light coming into it by sampling the light equally from all parts of the image, and then uses this average light reading as the correct exposure for the image. The problem with my wife’s photo was that while the part of the image where sunlight was falling on her face was extremely bright, the rest of the image was significantly darker.
To describe this simply, let’s say that the intensity of the light coming from the lit part of her face is measured by a number, & let's say that this number was 5, while the intensity from the dark part of the image was significantly lower at 1. The average intensity of light would work out to 3, which is what the camera would set as the exposure. (This is a very simplistic explanation, & in reality how the camera sets the exposure is nowhere as simply arithmetical as this). Now when the image is exposed at 3, what happens is that the while one gets to see some details from the dark areas of the image, the bright areas get totally over-exposed, resulting in the problem that I faced.
Now, don’t take this to mean that using the matrix metering mode is wrong. In fact, Nikon’s matrix mode is justly famous for giving excellent exposures for most images. To the best of my knowledge, a lot of pros simply put the camera of matrix mode and trust Nikon to handle the exposure. It is only in special cases like the one described above, where the matrix mode does not turn out to be the right solution to the problem. Here is an example of a recent photograph taken using the matrix metering mode. As you can see, the image is overall decently exposed, so the mode obviously works well.
So, getting back to the photograph of my wife, you can understand how important it was for domestic peace to figure out how not to make such mistakes again in future. Well, with such high stakes at play, I did figure out the solution, & here it is.
The ready-made, in-camera solution is to switch to the “spot” metering mode when you are photographing such situations. (In Nikon cameras, this mode is visually identified by a square with a dot in its centre).
In spot metering, when you focus on a certain point in the image, the camera sets the exposure for that spot, so that the point of focus is not just properly focused, it is also perfectly exposed. So, going back to the example of my wife’s photo, if I had used spot metering and focused on the part of her face on which light was falling, then that part would have been perfectly exposed, showing all the details, and thus avoiding the problem that I faced.
Simple, isn’t it? However, one also needs to understand how this will impact the rest of the image. In my example, since the exposure would now be set for the brightest part of the image, the shutter speed would be much higher than in the matrix mode. This means that the darker parts of the scene would be under-exposed, & would therefore appear to be very dark(close to black), & you may not be able to see any details in those parts of the image. Therefore, you need to be clear whether this is the effect you want before you choose to use spot metering.
Here is an example of an image where I have used spot metering to ensure that the bright part of the image is properly exposed.
In this case, the rose was lit up by the sun’s rays and I was shooting against the light. By spot metering on the brightest part of the rose , I was able to retain enough detail there so that one can see the folds of the petals even in this part of the image.
Other than these two, there is a third mode of metering called the “centre-weighted” metering. In this mode, the camera assigns maximum weightage to the light it received from the centre of the image, & correspondingly reduces the weightage as one moves out concentrically towards the edges of the image. I have found this mode very useful for shooting sunsets, and for shooting silhouettes of people against some bright light or against the setting sun. Here is an image in which I have used centre-weighted metering.
Now that I’ve talked about metering, it’s time to get down to the practical issues. For example, where would you find the metering option on your camera? Since I own a Nikon D80 camera, let me show you where to find the option on that. If you own a Canon or any other brand, I assume you would be able to find this option without too much difficulty.
In the photo of my D80 below, what you need to do is to press the button in the darkened circle at the top right side of the camera(immediately above the LCD screen), and then rotate the wheel in the brownish area at the bottom right of the camera(next to the strap), to shift from one metering mode to another. When you do so, the metering mode selected is displayed on the LCD screen.