Exposure Triangle (Part 3) – Aperture

So far, we’ve talked about the three main elements in the exposure triangle, and looked in more detail into Shutter Speed. Our next stop is with the “Aperture”. If you don’t remember the theory from the first post in this series, you can read the post all over again by reading again the How it’s Made post or the Exposure Triangle introduction. If you don’t feel like reading these articles again, just keep in mind that the Aperture is a variable-diameter hole in a lens-construction, which we can make wider or narrower, depending on whether we need more light (wider) or less light (narrower) to enter the camera when we make our exposure (by pressing the shutter button).

As with the Shutter Speed, which we covered in Part 2 of this series, using a wide or narrower aperture is not just a decision based on how much light we want to get in our image. There is another factor to take into consideration, and that factor is “depth of field”. This post explains this phenomenon, hopefully in simple enough terms for everyone to understand.

So, what is Depth of Field? In simple terms, Depth of Field (DoF) can be defined as referring to the area in front of and behind a subject in focus. The DoF available to you is not something static – it changes on the basis of the Aperture value selected (although not exclusively). As a general rule,  (and assuming you are focusing on a subject), the wider the aperture is opened, the shallower the DoF becomes – that is, you will have a very small area in front of and behind of the subject focused on that also appears in focus, with the rest looking more blurred. On the other hand, the narrower the aperture is, the larger the area in front and behind of the focused subject becomes. Let’s look at an examples, as it’s best this way!


Above are two photos, side-by-side of the same scene. In both images, focus was locked on the red plant. Notice how the background is clearly more blurred in the wide-aperture shot. The main difference between the two is in fact the result of a different Depth of Field available – in the first image the aperture was f/1.4, a very wide Aperture in photographic terms. The other image is f/8.0, which translates to a difference of five (5) “stops” of light.

Now, this might get technical – what five stops of light implies is that the amount of light coming in at f/1.4 is substantially more than what is coming in at f/8.0. For clarity’s sake – One (1) stop of light more equals to twice as much light coming into the camera, and of course, one (1) stop of light less equals to half as much light coming into the camera. So how much is five-stops of light more? Easy – That’s 2 x 2 x 2 x 2 x 2.  Or for the more mathematical among you, 2 to the power of 5. The answer is 32 – which means that f/1.4 allows 32 times more light into the camera than an aperture of f/8.0. Or else, we can say that f/8.0 allows 1/32 times the amount of light to pass through when compared to f/1.4. The maths is reversible.

If the above lost you, remember the essential stuff:

  1. Wider aperture = More light, Shallow (less) Depth of Field.
  2. Narrow aperture = Less light, Wider (more) Depth of Field.
  3. One (1) “Stop” of light more allows double the amount of light to enter the camera.
  4. One (1) “Stop” of light less allows half the amount of light to enter the camera.

Hope this was informative and leave comments or queries if you have any doubts!

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4 Responses to Exposure Triangle (Part 3) – Aperture

  1. Pingback: Exposure Triangle (Part 4) – ISO Sensitivity | ALISTAIR FARRUGIA | photography

  2. Pingback: The “Correct Exposure” – Part 1 | ALISTAIR FARRUGIA | photography

  3. Pingback: The “Correct Exposure” – Part 2 | ALISTAIR FARRUGIA | photography

  4. Pingback: Exposure Modes | ALISTAIR FARRUGIA | photography

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