Niagara falls at sunrise. Choosing the correct shutter speed and aperture allowed me to show motion in the water and have the whole image in focus at once.
Before going into long discussions of the physics of photography or describing the technical aspects of some of my best pictures or telling you how to get the best picture possible it is important to understand the basics of photography. 95% of people taking pictures do so with their camera on auto mode, letting the camera decide what kind of picture to take. If you are just trying to get snapshots of memories then this works rather well. The camera has a very intelligent system for picking settings and will get you a decent picture 90% of the time. However the best you will most likely do is snapshots, whether you have a cell phone camera or $10,000 in equipment the result will be the same. In order to understand how to take your pictures from good to great to amazing first we need to get that camera off of auto mode and learn what all those buttons and dials actually do!
The Holy Camera Trinity
Taking a picture comes down to three important aspects in a technical sense. Those three parameters are shutter speed, ISO, and aperture. We will take each of these separately first and then talk about how they interact with each other to give you a final picture. This technical aspect of photography is often overlooked when you have a good eye and a highly trained artistic look on the world, but in order to take a picture from concept to reality you need to know how to master the technical as well as the artistic side of photography.
This is the parameter people are most familiar with and also where we will start. The shutter speed is how long the camera sensor is exposed to the light. This can vary from 1/4000th of a second to up to hour long exposures. The faster the shutter the less light gets in and the more “frozen” the scene appears. For faster shutter speeds of about 1/100 s and faster you will essentially freeze the scene. This will vary depend on how fast the thing you are trying to photograph is moving. Generally we use fast shutters to stop the motion in a photograph and make everything appear sharp and in focus. If you want to convey a sense of motion in the picture you can use a slower shutter speed to give a motion blur effect. Longer exposures/shutter speeds are needed when there is not enough light or you want to convey motion in a slow moving object. Things like the Milky Way are very dim and require longer shutter speeds to capture. The picture below was taken in Arches National Park in Utah.
This area is one of the darkest in the world, letting you see an unimaginable amount of stars. Since the sky and surrounding area is so dark a long shutter speed only collects the light of the stars, revealing them to the camera. A 30 second exposure allowed me to capture the stars but avoid any motion blur. Since the earth is rotating, motion blur is still a consideration when photographing the stars since the earth is moving relative to the stars. After about 30 seconds the stars would start to trail due to the earth’s rotation. If you want to try having semi-control over your camera's shutter speed try the T or Tv mode which allows you to set the shutter speed and let the camera adjust the other settings automatically for the correct exposure.
The aperture setting provides two distinct yet equally important aspects to your photograph. The aperture itself is the opening at the back of your lens that lets the light into the camera itself. This opening can be opened or closed down to let in more or less light. Whenever you buy a camera lens it will come with an aperture rating. For instance most Kit lenses that come with the camera are labeled as 18-55 f/3.5-5.6. The second part after the f/ is where we will focus now. In order to understand aperture it is important to know what that f/ means. This designation is called the f-number of the lens. The f-number of a lens is determined by the focal length of a lens divided by the diameter of the aperture opening. For instance a 50 mm lens with a maximum aperture opening of 27.78 mm would be f/1.8. A 50 mm lens with an opening of 17.85 mm would be an f/2.8 lens. As you can see the smaller the f-number the BIGGER the opening, and therefore the MORE light the lens can collect. When buying lenses, the lens will be labeled with the biggest the aperture can go, not the smallest. All lenses can be “stopped down” where the size of the aperture is decreased for the picture. Generally any lens can go down to f/22 which indicates a very small opening for the light.
You may be wondering, why would you want to close the aperture to a smaller size? There are two reasons to do this. The first brings us back to shutter speed. Say we want a slow shutter speed to capture some motion blur on the thing we are photographing. If we keep the aperture the same but just change the shutter speed then a longer exposure means that more light goes to the camera and thus the picture is brighter. In order to keep the same brightness level for a longer exposure we must decrease the size of the aperture in order to let less light into the camera. The other reason relates to Depth of Field (DoF), which is the amount of the picture that is in focus. We will talk about the specifics and physics of depth of field in a later post, but for now we will keep is simple. The smaller the aperture opening the more of the picture will be in focus. If we are photographing a sweeping landscape where we want everything from the close blades of grass to the furthest reaching mountains to be in focus then we would want a small aperture such as f/11 or more to get everything into focus at once.
Instead if we want to have something really stand out in a picture and be separated from the background then we will want to use a really big aperture such as f/2.8 or wider. When you see “professional” pictures where the people really POP and the background is a smooth blur this is because the person taking the picture used a wide open aperture setting of f/2.8 or larger. Small compact cameras such as cell phone cameras have a very small lens which does not open very wide, meaning you cannot get the large aperture sizes of a DSLR. Aperture is a very powerful tool in creating the picture you want, and one you should experiment with extensively to understand how it works. Most cameras these days have a setting called Av or A which stands for Aperture Priority mode. If you learn to use one mode outside of auto this should be it. What this mode does is allows you to set the aperture to a size of your choosing and then the camera changes all the other settings to get you the correct exposure. This allows you to control the DoF of the image and take either stunning landscapes or professional looking portraits. This is the setting I personally use for probably 60-70% of my pictures as it provides powerful control while still letting the camera do most of the thinking.
Just remember a BIG number is a SMALL opening and a SMALL number is a BIG opening!
The final component of the trinity is the ISO. We can have a lot of technical discussions on ISO and someday I hope we will, but for today we will stick the just the necessary parts. The ISO is the gain the camera uses to amplify the signal. Generally the base ISO is 100 where very little gain is used. As the ISO is increased the signal is amplified more and more. This is good for low light situations where you need a fast shutter speed but don’t have a lot of light to work with. Once you open up the aperture as wide as it can go, and if you want to, say, photograph a person in a dimly lit room you need a shutter speed fast enough to freeze their expression. However if the room is too dark you may be looking at shutter speeds of up to 1 second, which is much too long to both hold your hands steady as well as for the person to not move. The only option left at this point is to increase the ISO. At higher ISO you need less light for the same exposure meaning you can reach more reasonable shutter speeds, however at the trade off of more noise in your image. You are not only amplifying the light entering the camera but also the noise from various sources. This noise is what gives pictures a grainy look where the details are washed out and there are splotches of color throughout the image. In general the larger the camera sensor the better it handles noise since you are collecting more light overall and can therefore amplify it better. This is why trying to take a picture in a dimly lit bar with a cell phone usually doesn’t work very well, while a person with a DSLR might be able to get the picture with ease. In most situations I leave my ISO setting on automatic and let the camera determine what ISO I need for the shot. We will look at the interplay of these settings next.
Looking at the background you can see the grainy appearance of the picture. This shot was taken at ISO 3200 which was too high for my camera, washing out the details and giving a noisy picture. However the only way to get this picture was to increase the ISO since my aperture was fully open and I couldn't shoot at a slower shutter speed. It is better to have a slightly grainy picture then no picture at all!
Bringing the Trinity Together
Now that we’ve done a basic overview of these three important settings it is helpful to know how they interact. For this we will introduce stops of light. Each “stop” indicates a doubling or halving of the amount of light recorded by the camera. The goal of the cameras metering system is to have a well balanced where things aren’t too dark or too light. The easiest of these to understand is the shutter speed. Halving the shutter speed (say 1/100s to 1/200s or 10s to 5s) halves the amount of light and thus is a 1 stop decrease in the amount of light. This would make the picture 1 stop darker and thus underexposed. Doubling the shutter speed (2s to 4s) doubles the amount of light and thus increases the exposure by 1 stop, or makes it 1 stop overexposed. In order to compensate for this change and to make the picture the correct exposure you or the camera can change either the aperture or the ISO to compensate. ISO works in a similar way; where doubling or halving the ISO changes the stops by 1. Typical ISO values are 100, 200, 400, 800, 1600, 3200, 6400, and 12800 and correspond to one stop changes. Finally you can open or close the aperture more to change the stops of light. Since these are circles but are measured using diameters the aperture changes are a little more complicated. We will start with a fully open aperture of the biggest size commonly available of f/1.4. From there full stop changes are f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.
We can use this information to find “equivalent” settings where we get the same exposure but vastly different pictures. Let’s start with a picture where the cameras metering system tells us that f/1.4 aperture, shutter speed of 1/250 and an ISO of 100 gives us the correct exposure. This will give a very shallow DoF, with no noise and very frozen scene. We can get the same exposure by using f/11 (+6 stops), shutter speed of 1/4s and ISO 100. Now we have the same exposure but with a lot of DoF and a very slow shutter speed. At this speed we would need a tripod as you cannot hold a camera steady at 1/4s without having a blurry picture. You can do a whole lot of in between settings that aren’t as extreme such as f/5.6, 1/60 and ISO 400 which is an average mix of DOF, shutter speed and ISO (these are probably the settings your camera would choose on Auto). This is where the beauty of A or Av mode comes in. You can set your aperture as you please then the camera will adjust the shutter speed and ISO automatically to keep the right exposure. In general the camera will slow down the shutter speed until it reaches ~1/focal length and then increase the ISO. The reason for this is that most people can hand hold the camera down to 1/focal length without causing blurry pictures. For instance a 100 mm lens can be hand held down to 1/100s but will need a tripod for slower shutter speeds. This is just a rough rule and your mileage will vary but it generally hold true.
Hopefully this gave you a pretty good idea of how your camera settings work together and how to start thinking about them when taking pictures. I encourage you to get your camera off of auto mode and experiment with the other modes to give you control over the settings. You will find that it may be hard to keep track of your settings at first, but as you experiment and get used to it you will quickly see an improvement in your pictures and getting the look you want.