In part one of this series you kicked your digital SLR camera's auto mode to the curb with the help of program mode. In doing so, you learned to control the flash, the ISO value, and the white balance. Now in part two we're going straight to manual mode to learn about aperture sizes and shutter speeds. So let's do this thing. Put your camera in manual mode by turning the mode dial to the "M" setting as pictured above.
Your camera is basically just a box with a hole in it and a light sensor inside. If the right amount of light gets through the hole to strike the sensor, you get a properly exposed picture. If you get too much or too little light, you get garbage. You already know that in program mode you can control the sensitivity of the light sensor itself by changing the ISO value, but in manual mode you can also control the amount of light that gets inside in the first place. You do that with the shutter and the aperture.
The shutter controls how long the hole in your camera stays open. Open it for a long time and a lot of light gets in. Open it for a short time and less light gets in. It's that simple!
Well, not really. Having a fast shutter means you can freeze fast action such as athletic performances, splashing water, and so on. The drawback? A lot less light gets inside the camera, and your picture could be too dark. Conversely, you might use a slow shutter speed to compensate for low light conditions—the longer the hole is open, the more light gets in, right? But there's a drawback here, too. With a slow shutter speed it's more likely that you or your subject is going to move while the shutter is open, causing motion blur in your photo.
In auto mode and program mode, the camera decides what shutter speed is needed. Sometimes the result is what you want, sometimes it isn't. The camera doesn't know that you want to freeze a fast-moving subject, for example. All it knows is whether the right amount of light is getting inside the camera for a proper exposure. With the camera in manual mode, however, you control the shutter speed to get the shot you really want.
To change the shutter speed in manual mode, just turn the command dial (1) and watch for the changing numbers in the LCD status screen (2).
While shutter speed is how long the hole in the camera is open, aperture is best thought of as the size of the hole itself. The bigger the hole, the more light gets in. The smaller the hole, the less light gets in. Aperture sizes are expressed in "f-stops." Confusingly, a large f-stop number means a small hole, while a small f-stop number means a big hole. Thus, f/4 would be a large aperture opening and f/11 would be a smaller one.
You might want to use a large aperture, say f/3.5, to compensate for a low light situation, but there is a side-effect to think about: depth of field, or DOF. A large opening (small f-stop number) gives you a very shallow DOF, and a small opening (big f-stop number) gives you a much deeper DOF.
What does DOF really mean? Look carefully at this composite photo of a back yard tiki torch. The left side was shot at f/22: The torch is in focus, and you can make out the tree and the house behind it. That's a large DOF. The right side, on the other hand, was shot at f/2.8: The torch is in focus, but the trees and the house are melted beyond recognition. That's a shallow DOF. Great portraiture often uses a shallow DOF to isolate the subject. When shooting a landscape, however, you usually want everything to be in focus.
When in manual mode, change the aperture size by pressing the aperture button (1), rotating the command dial (2), and observing the value in the LCD (3).
Putting it all together
So you have these two parameters, shutter speed and aperture size, both of which do essentially the same thing: control how much light gets in. You get the same amount of light with a large aperture and a fast shutter speed as you do with a small aperture and a slow shutter speed. Get it? If you have a big hole that's open for a short time, it's kind of like having a small hole that's open for a longer time. The result is the same amount of light getting in, or the same exposure.
So what's the difference? It's all in those side effects I mentioned. Sometimes you want a fast shutter speed to freeze motion, sometimes you want a large aperture to get a shallow depth of field, and so on. You need a certain amount of light to get into the camera, but in manual mode you choose how to get that amount based on the other things you want for the shot. In auto mode and program mode, the camera usually chooses middle-of-the-road aperture and shutter settings, getting a good exposure but avoiding any extremes—and any creativity as well.
Remember, ISO value is a factor, too. If you wanted to take an indoor picture of an athletic performance, such as this martial artist flying through the air, you know you need a fast shutter speed. But you also know that at that speed you risk not getting enough light for a proper exposure. What to do? Crank up the ISO! Light is scarce indoors, and at a high sensitivity like ISO 800, your camera doesn't need as much of it. You should also go to the largest aperture you have: f/3.5 or even f/2.8 if available. If you do these things, you're going to be able to get a proper exposure even with the fast shutter speed you need to freeze the action. Your shot may suffer from some noise, and the shallow DOF may cause things behind the player to become blurred, but so what? It's better than not getting the shot at all. Photography is all about trade-offs.
Here's another example. Suppose you want to shoot a portrait outdoors in the daytime. Having a shallow DOF in this case is good. Blurring everything but your subject draws attention to it, so set a large aperture, at least f/4. With that big of an opening, however, you might get too much light in the camera and your picture could be overexposed, almost a whiteout. What can you do? First, make sure you're shooting at the lowest ISO setting. Second, make your shutter speed very fast—try 1/1000th of a second. Doing these things will allow you to get a proper exposure—even though you have a large aperture opening in bright daylight.
If you get it wrong, don't worry! Take a shot, look at it in the LCD screen on the back of your camera, and adjust accordingly. Experienced photographers guess pretty well at the settings that will work in a given environment, but even they check to make sure.
Shortcuts: Priority Modes
All of this is a lot to remember. Juggling f-stops, shutter speeds, and ISO values in your head while trying to compose a shot can be tough, especially for beginners. Maybe you're even thinking of forgetting this whole thing, sticking with program mode, and never delving any further into the workings of your camera.
Don't give up! Here are two shortcuts which will reduce the amount of thinking you have to do, while still getting you the shot you want. You may want to kick me for not telling you about these earlier. The two shortcut modes are aperture priority mode ("A" or "Av"), and shutter priority mode ("S" or "Tv"—literally "time value").
Let's say you're shooting that basketball player again. What do you really care about? Shutter speed. That's what you need to freeze him in mid-air. The only reason you're fiddling with the other two settings is to compensate for your fast shutter needs. Using shutter priority mode, you can make your camera do some of this work for you. Putting the dial on "S" tells your camera "I am deciding the shutter speed, you set the aperture for me." You'll still need to choose a sensible ISO value, but the camera will calculate—based on the light in the room and the shutter speed you have chosen—what aperture setting is required for a proper exposure. Handy!
You change the shutter speed in shutter priority mode the same way as you did in manual mode: Rotate the command dial and look for the changing numbers in the LCD status screen.
Aperture priority mode works in much the same way. When you're taking that sunny day portrait, what do you really care about? The aperture. That's the setting you need for the shallow DOF effect you're looking for. The only reason you're changing the shutter speed is to make sure you get a properly exposed shot. But again, you can make the camera do some of the work for you. Turning the mode dial to "A" tells the camera "I have chosen f/4, and you, Mr. Camera, are to figure out what shutter speed I need." Simple as that. You still need to select a sensible ISO, but the correct shutter speed is figured out for you.
Since aperture is the main event in aperture priority mode, you may not need to press the aperture button; simply rotate the command dial and look for the changing numbers in the LCD status screen.
Now that you know all this stuff, here's a couple of things to try. Find some sports action: Kids on skateboards, someone catching a Frisbee, whatever. Put your camera in shutter priority mode and crank it up to 1/800th of a second or higher. Select a high ISO value if you're indoors and a lower one if you're in daylight. Take some pictures. Did you freeze the action? If that Frisbee looks motion-blurred, try cranking up the shutter speed some more. If your photos become a little dark, bump up the ISO again.
Then take a walk in the park with a friend and shoot some portraits. Put the camera in aperture priority mode and go for the largest aperture you have: probably f/3.5. Frame a tight shot and take the picture. Did you get that soft, blurred background to make your friend stand out? (Bonus experiment: Stand your friend in the shade and pop up your flash!)
If you're really feeling bold, try going to manual mode where you control both the shutter and the aperture yourself. I recommend doing this only when you aren't going to be rushed. Take a walk by yourself and shoot a tree or a park bench. Subjects like these don't get impatient when you take four or five test shots to get your settings right.
Taking control of the shutter and aperture isn't easy, but the rewards can be great. Understanding how they work allows you to do more than just get the right amount of light into the camera, it enables you to get the artistic results you want; the results no camera could ever choose for you. Remember to use the shortcut modes, aperture priority and shutter priority. They're there to make your life easier.
Congratulations! No mere button-pusher, you. Not anymore. You're well on the road to becoming a real photographer. All you need now is practice. So get going, and happy shooting!