Photography Basics: Shutter Speed, Aperture & ISO


I was camping this weekend when a few people and we got into a conversation about photography. One of the people is totally into the hobby, but isn't too well versed with the technical side of things yet. She takes awesome photos and has a really good handle on composition and lighting, but tends to use the "helper" modes her camera offers. You know, the sports, landscape, portrait and whatever other mode the camera's got. They're all on one side of the dial, sitting nicely together. The little flower, man running, mountain, etc...

When we began talking, I tried to persuade her to move away from those easy modes and to explore the more serious modes, such as shutter priority, aperture priority and full manual mode. It was then that I realized that she didn't have as good a grasp on the exposure triangle as I did. She needed to get caught up to speed. Not a problem, as I love talking about photography. Actually, I was probably somewhat annoying because I didn't shut up for half the night.

Anyway, I thought I'd share a quick post here that covers what I told my friend the other night. I tried to break things down in the most simple way I knew how. I suspect I did a fairly good job of it because she seemed to understand what I was saying. I did realize though that the topic is confusing for someone who is a beginner, so I didn't include any bells and whistles with what I was telling her.

Here's what I told her:

There are three primary parts of a camera's exposure. and by exposure, I mean light hitting the camera's sensor to create a photograph. Each of these parts controls light as well as offers an effect. Each is a trade-off with another. If you want one thing, you'll likely have to give up another. Here's what I mean.

Shutter speed controls how much light hits the sensor, but it also controls how much blur is incorporated into an image. Basically, you've got your camera's sensor sitting there behind the shutter. You go into shutter priority and tell the camera how long to hold the shutter open. The longer the time, the more light that's allowed to enter. So, if you need a lot of light, having a long shutter speed is a great way to go. The only problem with that is that with long exposure times (long shutter speed times), you get a lot of blur if the camera isn't held completely still. While the shutter is wide open letting all that light in and you move the camera, you'll see trails when looking at the final image. Conversely, if you have a super fast shutter speed, not much light at all will be let in. You won't get any blur, but you also won't get much light. There's your first trade-off. Light versus blur.

The aperture (hole in the lens that lets light through) in a lens is another apparatus that can control light that's entering the camera. When you change your camera to aperture priority mode, you're essentially telling your camera how large you would like the hole in the lens to be. Obviously, large holes let lots of light in and small holes don't. The thing is, large holes also create a shallow depth of field, meaning there will be a lot of blur in the foreground and background of your photos. If you're taking a portrait of someone on a bright sunny day and you shrink your aperture down so it's very small, to compensate for all that light, you're creating a deep depth of field as a byproduct. This means that the foreground, subject and background of your image will be sharp. This is highly distracting in portraits, so many people either use a sun filter or a fast shutter speed to cut the light and then open up their aperture to get that blur they're after.

Finally, ISO controls how sensitive the camera's sensor is. Low ISO values make the sensor less sensitive and high ISO values make the sensor more sensitive. If you wanted a high exposure image, you could set the ISO value in your camera to something high, but then you run the risk of introducing grain into your images. Low ISO values don't have a lot of grain (noise), but high ISO values do. See? There's another trade-off. So if you want a high exposure image, you'd probably want to keep the ISO value under 800 and either open up the aperture or set a longer shutter speed, depending on what your goal is.

Well, that's what I told her. I knew it sounded confusing to a beginner, but I promised that the idea behind everything would come together the more experienced she became. I hated that I couldn't make it more clear, but it is what it is.

Do you have a better way to explain the exposure triangle as it pertains to photography? If so, please let me know below. Thanks!