Photography requires greater technical understanding than any other art form. I’ve been teaching people at all levels of photography for well over a decade. At the start of each workshop, I always begin by explaining metering and basic exposure settings. A major foundation of good photography, these settings are often the least understood, but they are among the easiest things to get right.
Before We Start
Last time, I wrote about how to buy your first camera. This and my future articles will focus on how to use it. There is a lot to learn, and I will break it down into bite-sized pieces. In this article, we are discussing metering and exposure. Everything that follows is a simplified version of what is happening. My intention is not to delve into the intricacies of quantum mechanics and the physics of photography. Instead, I want to help you, the novice photographer, understand what happens when you adjust your camera’s settings.
How Do Metering and Exposure Work?
I use a simple analogy to help my clients understand the concept of exposure.
Imagine holding a small drinking glass under a shower. Covering the top of the glass with a lid, we call it a shutter. You turn on the shower. When you remove the shutter, it takes two seconds for the glass to fill to the top. You then put the shutter back on before the glass overflows.
Obviously, if you removed the lid for just one second, the glass would be half full. That’s what we want to achieve from now on, just half-filling the glass.
The same applies to light reaching the sensor. In simplest terms, you can think of it as needing to be half-filled with droplets of light. If the sensor were empty, the resulting photograph would be black. Equally, if the sensor were full, the picture would be white. So, you want to fill it halfway, to mid-gray.
Adding an Aperture
Next, you place a piece of card to cover half top of the glass, leaving a smaller opening, or aperture. You now need to remove the shutter for double the time – two seconds — to half fill the glass. If you halve the aperture’s size again, it will take four seconds to half-fill the glass, and so on.
Similarly, camera systems have apertures and shutters. Light passes through the lens’s adjustable aperture. The smaller the aperture, the longer the shutter must remain open to let the same amount of light through.
When the Light Changes
Let’s return to my analogy. If we increase the water flow of the shower, the glass will fill more quickly. If you reduce the stream, it takes longer. That is equivalent to photographing on a bright or dull day. As more light droplets pass through the lens, you need to increase the shutter speed or decrease the aperture to gather the same amount of light.
Just as you can measure the amount of water and know when the glass is half full, the camera can measure, or meter, the amount of light reaching the sensor. It knows when it is time to close the shutter.
It’s Not Just One Glass, It’s Millions
Instead of having one glass, imagine a tray full of glasses. When placed under the shower for one second, some glasses fill more quickly than others. Where there is a lot of water flowing, the glasses will fill to the brim. Meanwhile, some glasses will be half full, while others will not receive any water at all and will be empty. However, on average, they are half full.
When you shoot a photo, the millions of microscopic light receptors on the sensor, called photosites, receive varying amounts of light. Well-lit areas of a scene deliver a lot of light and make those areas of the picture bright. Other areas of the sensor will receive hardly any light, and the corresponding regions of the photo will appear dark. Meanwhile, all the remaining receptors will collect enough light to match that part of the scene.
Like the glasses under the shower, they average out at being half-full of light.
So, when you take a photo, the camera usually meters the entire scene and judges the average amount of light it needs. Consequently, it sets the exposure it thinks is correct by balancing the aperture and shutter speed.
It’s a bit more complex than that with a lot of variables, but let’s not confuse the matter for now.
ISO is a Dirty Word
We have discussed the amount of light, the duration of the shutter being open, and the size of the aperture. But there is one more adjustable setting: the ISO.
Returning to my analogy, on average, it takes one second to half-fill those glasses. But what would happen if we first quarter-filled them with sand? It would only take half a second to reach the halfway mark. Consequently, we can achieve a shorter exposure (a faster shutter speed). However, the water will be grainy.
In a camera, increasing the ISO amplifies the signal from the sensor inside the camera. Consequently, the sensor needs less light to be exposed correctly.
Most cameras are designed to give their cleanest images at ISO 100 (or 200 for Micro Four Thirds). If you double the ISO, the camera will need half the amount of light to expose correctly. This means the shutter will open and close twice as quickly, e.g., from 1/1000th to 2/2000thof a second.
With every advantage in photography, there’s always a disadvantage. The payoff here is that as you increase the ISO, the picture will appear noisier, with more speckles on it.
Why is that? If you own a hi-fi, turn up the volume with no music playing. You will hear a hissing or buzzing noise. That noise is always present and is produced by the electronics, but music helps drown it out. It’s the same in your camera. As you increase the ISO, you decrease the amount of light reaching the sensor. So there is less light to drown out the noise. That makes the noise more evident in the photo. The picture appears dirtier with a grainy texture embedded in it. However, it can be cleaned up using denoising software.
Why Change the Exposure Settings?
If you are reading this, it’s likely that you want to enhance your photography skills. Changing the aperture, shutter speed, ISO, and the amount of light available alters the appearance of a picture. I’ll go into each of those in more depth in future articles. If so, you’ll want to get your camera out of auto mode and take more control over your shots. In that case, understanding metering and learning to control exposure are essential first steps. Understanding them will help you override the camera’s default settings and achieve more pleasing results, especially in unusual lighting conditions.
Setting up Your Camera
If you want to take control of your camera and move beyond auto modes, setting it to aperture priority mode is a great place to start. You will find a mode dial on top of your camera, displaying P, A, S, M, and various other letters or symbols. Set it to A. If you own a Canon, it uses Av instead of A.
A stands for aperture priority and not auto. This mode allows you to change the aperture, and the camera will set the shutter to expose correctly. It’s a quick and easy way of adjusting your camera.
Next, look for a button or menu item labelled ‘ISO.’ Selecting this option should prompt you to change the setting, usually by spinning the command dial, also known as the adjustment dial. By default, the ISO is often set to auto. Change it to 100, or 200 if you own a Micro Four Thirds camera. Every camera is different, and you may need to refer to the manual for instructions on how to do that.
Briefly half-press the shutter release button. On the back screen, or through the viewfinder, you will see a series of numbers. One of those will be fixed at 100 (or 200). That is the ISO you just set.
You should also see a smaller number. The letter f may precede it. This is the aperture. Depending on your lens, it is most likely to be set somewhere between f/1.8 and f/22. Use your command dial to make this number as small as possible. A lower f-number corresponds to a wider aperture. That allows more light to enter than a higher number, thus resulting in a faster shutter speed.
There will be a third number. On some cameras, this feature appears briefly after you half-press the shutter button, while on other cameras, it remains visible at all times. That is the shutter speed. If you point the camera at a bright light source (without looking directly at the sun), this number will increase. Correspondingly, it decreases as you point it towards the shade.
That number is a fraction of a second, showing how long the shutter is open. For example, if it says 1000, it means 1/1000th of a second, and 60 is 1/60th of a second. If the number is followed by “, it is whole seconds.
An Exercise
Take a picture of both a bright area and a dark one, and you should notice the shutter speed change. You might even hear the difference in sound between a fast and slow shutter speed. Now use the command dial to adjust the aperture and note how this changes the shutter speed as well. Go outside with your camera and practice. Familiarize yourself with the varying exposure settings. You will be using those in the following few articles.
In Conclusion
To summarize, we now know the camera meters the amount of light in the scene. It can then adjust the exposure settings to collect the correct amount of light. In aperture priority mode, you choose the aperture. With the ISO fixed, the camera changes the shutter speed according to the amount of light available.
What Comes Next?
That is your very first exciting step into the world of photography. Next time, we will discover the aperture and its impact on the appearance of the photograph. Then, in the following pieces, we shall gradually expand that knowledge, providing you with the complete set of skills to become a fully competent photographer.
Please bookmark this page so you can return to it, and click on my name to subscribe to future articles. But, most importantly, go out and practice.
