Exposure is a word that is used a lot in photography. We’ll talk about getting a good exposure, or we might say, “The exposure is good in this image.” Or sometimes we might say the exposure is bad in this image. The size of a roll of film is measured in exposures. So, is exposure simply another term for an image or a photo? Sometimes, but not always. The good news, is that you’re already actually experienced in the idea of exposure, just from using your eyes. In photographic terms, when we speak of exposure, we’re usually simply referring to how much light the camera is capturing. Your camera is just like your eyes, in that it requires a certain amount of light to be able to see detail in a scene. Now, you already know that when there’s not enough light, you can’t see. Your camera has the same problem. From time to time, you might also have encountered a situation with too much light, which also makes it hard to see. Again, your camera has the same problem. So, at the simplest level, exposure is simply a measure of how much light the camera is capturing. Now consider this image of me that you’re watching right now The camera is currently configured with exposure settings that are capturing an image that is this bright. If we adjust the settings, we can brighten the image, or darken it. We refer to that as changing the exposure. Another way to think of it, is that the camera’s image sensor is getting exposed to more or less light, depending on our settings. As those exposure settings change, the final image gets brighter or darker. So what’s the correct level of exposure? There’s rarely a single correct answer to that question. It depends partly on what it is that you want to see in a scene. For example, with the exposure settings that we’re currently using, you can see good detail on my skin, but look at this dark area, the area that’s in shadow. You can’t see anything over there. And you may think that’s simply because there’s nothing to see, but there is. But not with our current exposure settings. If we change the settings on the camera to brighten the scene, we can bring out the details in that shadowy area, but in doing that, we lose the details in these bright areas. Details that we were able to see before, they have now gone out to complete white. These areas that were completely dark, are now, are now visible. That’s a garden gnome with sunglasses… When we speak of an image having a good exposure, we’re usually referring, simply to how well we can see the important details in the image. Are they lost in shadow? If so, then we might say that the image is under exposed, it didn’t get enough light. If details are blown out to complete white, we say the image is over exposed, there was too much light. As you study exposure more, you’ll learn that it has other impacts on your image. From color reproduction to what, in your scene, is in focus. But for now, all you need to know, is that you control the overall brightness of your final image by adjusting your camera’s exposure controls. As you change exposure, the image will get brighter or darker, and different details in the image, will become more or less visible.
If I hold my hand up in front of my face, in front of that light fixture that’s up there, I shield myself from some of that light. Now from where you are, you can see that I’m casting a shadow onto my face with my hand. But that’s not how I think of it. I simply think of it as, blocking light that was striking my eyes. If I open and close my fingers or move my hand forward or back or in and out, I can block more or less light, in other words, I can control the exposure of my eyes to that light source. My eye has a built-in mechanism for doing this called the pupil or iris. You’ve all probably seen somebody elses’ pupils open and close or watch your own in a mirror. As the pupil closes, less light can enter the eye and strike the light-sensitive cells on the back of the eyeball. In this way, as light levels in the room brighten, my eyes can lower their exposure to that light. Conversely, as light levels dim, my pupils will get much larger to let in more light. I can also put on sunglasses to lower light levels. There are many different mechanisms available to me for controlling my eyes’ exposure to light. In the last video, we talked about controlling your camera’s exposure to light to render images brighter or darker. As there are many ways to control the light that strikes your eyes, your camera has three different mechanisms. First, it has a shutter. This is simply a door that sits in front of the sensor. It can open and close and depending on how long it stays open, the image sensor in the camera will be exposed to more or less light. This is known as shutter speed. We might refer to an image and say that image was shot with a shutter speed of 1/60 of a second, meaning that the shutter was only open for a 60th of a second when we took the picture. Shutter speeds can be very fast. This camera can shoot with shutter speeds up to 1/8000 of a second or they can be very slow, astrophotographs are sometimes shot with shutter speeds that measure in minutes or even hours. Shutter speeds pretty intuitive. The longer that little shutter is open, the more light that will hit the camera’s image sensor and as more light strikes the sensor, the image will get brighter. Your camera also has an iris that functions like the iris in your eyes. It’s a series of interlocking blades that create a circular opening that can be made bigger or smaller. As the opening gets larger, more light passes through and your image gets brighter. We refer to this as the aperture or iris and its size is measured in f-stops. Understanding the relationship between the f-stop scale and the size of the aperture can be a little confusing so we’re not going to go into that in this course. The third parameter is called ISO and it’s simply a measurement of the sensitivity of your camera’s image sensor. We can adjust that sensitivity to make the sensor more or less responsive to light. Anytime you take a picture, the light will be focused through your camera’s lens where it will be passed through the aperture which will be open to whatever size you have specified to allow more or less light. Then the shutter will open and close at the speed that its currently set for letting that light pass through where it will strike the image sensor. How much of that light will get recorded is dependent on the sensitivity of the sensor. These three parameters are things you’ll think about anytime you take a picture. Each one has several different effects on your final image and the three parameters together have a powerful intertwined relationship. A deep understanding of exposure requires a fair amount of study and we have an entire course set aside for it. Fortunately, your camera’s auto-mode can take care of a lot of the exposure decisions for you. This is great for the beginning photographer because it means you can go ahead and start taking good pictures. You can begin practicing composition and shooting technique and you can slowly begin to chip away at an understanding of exposure. Those are the things we’re going to be doing in the rest of this course.
Before you take a picture your camera needs to be told what shutter speed to use, what aperture setting to use and what ISO setting to use. Now depending on how you have your camera set up you might have to specify all those parameters or you might only have to specify one or two. Or you might not have to specify any at all if the camera is in full auto mode. However, whether it’s you or the camera making these choices there’s still the question of what the parameters should be set to. Answering that question is what a light meter is for. A light meter is a sensor that lives inside your camera. It can look at the light that’s coming through the lens, measure it and then calculate shutter speed, aperture and ISO settings that will give you a good overall exposure. You know people often refer to sliced bread as being the measure for the greatest thing and I think they only say that because they never tried to calculate exposure settings without a light meter. Doing that is much harder than slicing bread. So I would say that the light meter is the greatest thing since the light meter actually. Modern meters are incredible pieces of technology that can handle incredibly complex lighting situations. Most of the time your camera’s light meter will choose good settings. But there are times when the meter can get confused. But as you get more experience it will become easier to know when you might need to override the meters ideas. After you’ve framed your shot you activate the light meter by half-pressing the shutter button. So about halfway down you’re gonna feel the button give a little bit. That’s the point at which the camera activates the meter. It does some other things at this point as well. It focuses, calculates some color settings. We’ll talk about all that later. When you have half-press the meter measures the light in the scene, it analyzes it and then it sets the shutter speed and aperture on the camera. It might also set ISO depending on whether your camera is set to Auto ISO. It then beeps at you to let you know that it’s done its calculations. It might also flash a little light in the viewfinder. And then it tells you what settings its chosen. In your viewfinder or underneath the viewfinder some numbers are gonna appear. So what you’re seeing here on the monitor is what my camera is seeing right now. We’re looking at this nice little still life of these old cameras and you can see some status indicators down here. This is showing me my battery life, this is showing me how many pictures remain on the card, how much space I have on the card. if I half-press the shutter button a bunch of new stuff appears. Now you didn’t hear it beep and that’s because when we’re taking the video out of the camera to show on this monitor it kills the beep. Normally I would have heard it beep right about then but I’m seeing some other things here. I’m seeing 50, 5.6 and ISO 400. These are the exposure settings that the light meter has chosen. 5.6 is my aperture setting. That’s a measure of the size of the opening of the aperture in the lens. 50 is my shutter speed. This is a fraction. It’s the denominator of a fraction. So what this means is 1/50 of a second. Your camera might show things in a different order. in different places in the viewfinder. It might actually write out an entire fraction. It might say 1/50. But this for right now is the only number that I want you to worry about. This shutter speed number right now. We’ll talk more about it later. So now that it’s beeped I look at those numbers, i see what they are. If I’m okay with them I can then press the shutter button the rest of the way and the camera takes a picture using those settings. Half-pressing the shutter button like that is a critical habit that you need to develop right away. If you’ve ever missed the moment you were trying to photograph because there was a lag between the time that you pressed the button and the time when the camera actually took the picture that’s probably because you mashed the button all the way down like that. it takes time for the camera to meter the scene, to focus, to do its other calculations that it has to do. And if you don’t give it that time by half-pressing the button and waiting for it to tell you that it’s ready then you’re gonna miss the shot. So how do you know if the settings that you’ve chosen are good? That’s a huge question that depends on what details you want to capture, what type of image you visualize. What you might want to do is post-production. In this course we’re only going to concern ourselves with one level of exposure analysis. Like I said, that’s shutter speed and we’re gonna look at that because of the effect that it has on the sharpness of an image.
Most of the time you want the details in an image to be sharp and clearly defined. I say most of the time because there might be occassions where you like a soft or blurry image for stylistic reasons. But those occasions are rare. In most situations, it won’t matter how great your subject matter is or how wonderful the light is if the important details in your image are soft or out of focus. Now some lenses are inherently sharper than others, and a camera with a higher pixel count will be able to record more detail and therefore sharper images. You’ll want to consider that when shopping for a lens and camera. But when you’re shooting there are two factors that will define the sharpness in your image. The first, of course, is focus. If you don’t focus properly, then your image is going to be blurry. We’ll talk about focus in the next chapter. The second parameter is shutter speed. This should be fairly intuitive. A fast shutter speed captures a very thin slice of time; one where in motion is frozen and rendered very sharply. A slower shutter speed captures a thicker slice of time, and if something in the frame is moving quickly enough, it will be rendered soft or completely blurry. Therefore, when shooting moving objects you need to use a faster shutter speed. But motion in the frame isn’t caused solely by things in your scene moving about; if the camera itself is moving and your shutter speed is long enough to capture that movement, then your entire image will be blurry. For this reason, it’s imperative that you learn to pay attention to shutter speed when you’re shooting. Even when you’re in auto mode and the camera is handling all of the decisions and settings for you, you still need to know if you’re at risk of camera shake impacting your image. So, when you half-press the shutter button and the camera does its calculations and then it beeps, you need to develop the habit of looking at the resulting shutter speed number. If it’s too slow for handheld shooting, then you’ll need to take some action. Now what constitutes too slow for handheld shooting? In Foundations of Photography Exposure we’re going to take a look at a simple rule you can follow to get a very exact measure of the slowest shutter speed that you can use at any given time. But for now, we’re just going to call that slowest speed 1/60 of a second. So anytime you see that the meter has chosen a shutter speed lower than 1/60 of a second, you will know that you’re at risk of a shaky image. When you see that– let’s say the camera has chosen 1/30 of a second– when you see that, then you would ideally put your camera on a tripod. If you don’t have a tripod, then try to stabilize your body as best you can, find something to lean against, make sure your feet are shoulder width apart, keep your elbows at your sides and your back straight, take your time, press the button gently. Until the lighting conditions change, your camera will continue to choose that same shutter speed. Remember, the shutter speed was chosen because of the light meter’s analysis of the light in your scene. If the light doesn’t change, neither will the results of that analysis. So until the light changes, or until you move to someplace with different light, you will need to continue to be very careful about holding the camera steady. This is not a beginner’s problem. Watching shutter speed and thinking about camera shake is something I do every time I go out. But I also think about aperture and ISO and the effects that those have on my image. So right now, in addition to learning to consider shutter speed and handheld shake, you’re developing the habit of paying attention to the meter and compensating for what it might be telling you.