In last weeks post, DigiKnow covered Using Apertures in Photography (with Depth of Field in Image Making the week before). This week, we look at the Aperture/Shutter relationship to increase our understanding of the subject.

Apertures control Depth of Field (DOF) and impact shutter speeds used. Shutter speeds impact whether movement is frozen (static) or showing (non-static).

The relationship between aperture and shutter is very much like a dance. When you begin to learn any dance, you won’t get all the steps correct immediately and the same can be said in photography.

However, with semi-automatic modes, this is like being guided around the dance floor by a professional dancer where you are less likely to make mistakes.

Whilst using semi-automatic modes (Aperture or Shutter), novice photographers control one aspect of the settings and the camera compensates the other, i.e., the photography sets the F-number, the camera compensates the appropriate shutter speed and vice versa.

This ensures exposure is generally correct and leaves the photographer to decide which creative decisions are more important for the shoot, i.e., depth of field or movement.

Aperture/shutter relationship

Another way to view this aperture/shutter relationship can be seen in Figure 1 below:

The Aperture/Shutter relationship
Figure 1 – The Aperture/Shutter relationship

In Figure 1, apertures are at the top. Apertures toward the left are physically large (small F-numbers) and need little (fast) shutter speeds to make exposure acceptable. As the aperture gets smaller, slower shutters are required to keep exposures acceptable.

However, by closing down the aperture (going from large to small), several things occur:

  • Depth of field gets broader
  • Shutter speeds slow down
  • Seen movement is introduced

Another way to think about this is using the glass analogy, as seen in Figure 2 below:

Demonstrating Apertures and Shutters using the glass analogy
Figure 2 – Demonstrating Apertures and Shutters using the glass analogy

Imagine the amount of water is equal in both glasses and the water represents the amount of light required for the correct exposure.

In Figure 2, the left glass has a large aperture and the water/light comes out fast (shutter speed). Whilst the glass on the right has a small aperture and the water/light comes out slow. Both results in the correct exposure.

Many F-number/shutter combinations achieve correct exposure. The difference in results are visual, i.e., shallow/broad depth of field or frozen/shown movement as per Figure 1.

Task

Use a line of subjects going away from the camera, i.e., a line of cups, cloths pegs on a line, rocks on a wall, etc., as long as the subject is going away from the camera.

Ensure the focus point is the same in each image.

Using Aperture priority (A or Av), take 3 or 4 photos:

  • F3.5
  • F8.0
  • F16.0
  • F26.0

The only thing that you should change is the F-number and there are a number of things to notice:

  • How the camera adjusts the shutter (it changes automatically).
  • On playback, Depth of Field has changed between the first and last images.
  • It gets harder to handhold a camera at slower shutters AND maintain sharp images.
  • Exposure is acceptable in each image.
Summary

Semi-automatic modes are helpful for learners to quickly control settings whilst reducing the amount of decisions to be made. It allows for experimentation regards depth of field and movement whilst maintaining acceptable exposure.

Figure 1 demonstrated the relationship between apertures and shutters and how as aperture changes in a semi-automatic mode, shutter speed does too.

Although aperture controls Depth of Field and shutter speed controls how movement is viewed, the aperture and shutter speed are also two variables regarding exposure. The third variable is ISO.

Next week, DigiKnow looks at shutter speeds and ISO with different examples of how shutter affects movement and exposure. Do join us next week as we continue on with this series of posts in Making Images.

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