Capturing Light: An Overview of the Exposure Triangle in Easy Terms

Shutter speed example

Temple

Photography is, by definition, the art of drawing with light. So it’s not surprising that a great part of learning how to to take good photos is learning how to control light. In this section of my contemplative photography lesson plan, I’m going to discuss the three ways your camera helps you to do that. I am not going to talk about flash and external lighting setups, because frankly I have no practical experience with either, except for knowing that the built-in flash on your camera is really only good for giving your daughters glowing red eyes.

If you are shooting with a camera phone or a low-end point-and-shoot that doesn’t offer you much beyond auto shooting, I don’t know if this will be much help to you. I’ve taken some great shots with my iPhone 4, but I don’t know if there’s anyway to control exposure. (I may have to look into it though.)

Learning about exposure typically involves a lot of technical language about things like F-stops, which is the kind of thing used to separate experts from the rest of us. Now, when you look at those experts’ photos, you can see that their expertise pays off, but for the new or casual photographer it can be intimidating.

I am not an expert – I just like to take a nice picture once in a while – so I’m going to explain these things to you in the terms I understand them best. If you want to learn more, I encourage you to go out and find other resources who can provide more technical and expert guidance.

There are three basic tools on your camera that let you control light. They are:

  • Shutter speed
  • Aperture
  • ISO

Shutter speed and aperture control how much light enters through the camera’s lens. The ISO setting determines the sensitivity of the sensor, or how much light is actually recorded. (In film photography, ISO is equivalent to film speed, e.g. 100, 200, 400 etc.)

Shutter Speed

Shutter speed is pretty self-explanatory. It determines how long the shutter stays open, or how long it actually takes to snap the picture, and is measured in tenths (or even hundredths) of a second. Most of the time, you want to have a fast shutter, because the longer the shutter stays open, the greater the chance you’ll end up with a blurry photo. Your subject moves, your hand wobbles – it doesn’t take a great deal of motion to throw your focus out of whack. That’s why experienced photographers know to use a tripod when they are working with conditions that might require a long shutter speed (we’ll discuss some of those situations in a moment).

If you’re shooting in Auto mode, your camera will automatically select a longer shutter speed in low-light settings. You can tell, because the click sound you hear when you push the shutter button actually takes longer. If you’re out shooting in the woods, and all your gorgeous tree photos are slightly blurry, then it’s probably because the shutter is taking longer to open and close. The two solutions to this problem are: 1) use a tripod; 2) adjust your aperture.

Shutter speed example
Same aperture, different shutter speeds. On the left 1/8 second, on the right 1/25 second. Not only is the first overexposed, you can see how fuzzy the details are.

Aperture

Aperture refers to how wide the shutter actually opens – okay, not actually the shutter, but the hole inside the lens where light enters the camera. The wider the opening, the more light enters the camera at once. It’s measured as “f-stops”, which I’m not even going to try to define for you. It’s enough to say that your camera will have a range of numbers you can choose – mine goes from f/3.5 to f/20. But here’s the tricky part: the wider your aperture, the lower the number. So, an aperture of f/6 is open further than an aperture of f/10. That’s important, so I’m going to say it again:

The wider your aperture, the lower the f/number.

Okay – so what’s the point in being able to raise (close) or lower (open) your aperture? As I already said, it can help compensate in low-light settings, so your shutter speed doesn’t get too long. Or conversely, in strong light, raising your aperture can keep your photos from getting over-exposed or washed out. But there are consequences, and those consequences have mostly to do with what photographers call the Depth of Field.

Depth of Field refers to how much of what you are pointing the camera at will be in focus. With a wide aperture (low f-stop), only the subject you’re focused on will be sharp, while the background will be blurred. With a narrow aperture, everything in the camera’s line of sight will be sharp and clear. This has to do with the angle of light and how it enters the camera and, well, Physics. Don’t make me go there.

Aperture set at 5.6, 9.0 and 22 respectively. See how more of the background detail is in focus the higher the f-number goes? That's depth of field.
Aperture set at 5.6, 9.0 and 22 respectively. See how more of the background detail is in focus the higher the f-number goes? That’s depth of field.

To summarize (because it can be a little confusing at first):

Small f/number Wide aperture Shallow depth of field Good for:

  • close ups
  • portraits
  • macro
  • florals
  • bugs
Large f/number Narrow aperture Wide depth of field Good for:

  • landscapes
  • seascapes
  • sunrises/sunsets/clouds
  • sports
  • photojournalism

The Magic Dance of Shutter Speed and Aperture

When you understand the interconnected relationship between aperture and shutter speed, you have taken the first major step towards shooting with real artistry. In the most general terms, it’s about balancing the light that enters your camera’s lens. Raise one value, lower the other, to avoid under- or over-exposing your photograph. Then you can start making adjustments that will really allow your photos stand out from standard auto-set snapshots.

Aperture, in particular, is an easy way to control the final image, creating hazy backgrounds, blurred foliage, or the sparkling bokeh effect of blurred lights that is particularly popular. With a very wide aperture, you can focus tightly on your subject, while background objects fade into swirl of color and shadow.

Greening

I shoot almost entirely in aperature-priority mode, which means that I control the depth of field while my camera calculates the appropriate shutter speed for me based on its built in light meter.

Burst

You can also choose to shoot in shutter-priority mode, to control the time the shutter stays open. This is useful if you’re, for example, shooting animals or sports and you want to have a fast shutter speed to avoid blurring when the subject moves. Or you can lengthen the shutter speed to to create dreamy effects with moving water, or when you want to capture a shallow depth of field in low-light circumstances. (Just be sure to use a tripod.)

Cauldron

If you like a little math, then you can try shooting in full manual mode, which lets you set both the aperture and the shutter speed yourself – you’ll need to learn more about f-stops, and how much you’ll need to adjust shutter speed for such-and-such a aperture, and vice versa. Personally, that’s more than I want to tackle most of the time – contemplative -anything- does not involve math! I’m happy to let my camera handle the hard part.

That ISO Thing

You’ve doubtless noticed that though I mentioned ISO as the third part of the exposure triangle, I haven’t talked about it much yet.

That’s because, at least as far as I understand and use it, it’s kind of a last-ditch tool for me when it comes to exposure. If I want this shutter speed and that aperture, and my exposure is still too dark, then I raise the ISO to try and compensate. If there a better way to use ISO for artistic purpose, then I’m not familiar with it.

So, there you have the not-so-secret tools you can use to make sure your photos are properly exposed and also artistically interesting. Please feel free to ask questions and point out places where I can improve my descriptions – as I said, I’m no expert, just someone who has learned to muddle my way through the morass of expertise.

Next up in my Contemplative Photography Lesson Plan will be a couple posts about photo composition, so stay tuned!

 

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