Exercise – Focal Lengths for cameras with variable focal lengths

And so we’re on to focal lengths. I’ll come back to the Sequence of Composition exercise next weekend.

The purpose of this exercise was to understand the effect of changing a lens from one focal length to another, which on the face of it, may sound pretty straight forward. However, when combined with the next exercise, it shows the difference between changing perspective and angle of view.

The four pictures above are of Bradgate Park in Leicestershire from across Cropston Reservoir. The boathouse, which seems pointless apart from the vary rare occasions that the reservoir is full, is in the same position in each frame – I used the same AF focus point to line up the view. The camera was on a tripod and not moved during the exercise. What changes is the focal length. I started with my widest 17mm then zoomed to 40mm, swapped lenses and went from 70 to 200mm. Each view is effectively a crop of the previous. Nothing about the scene changes nor the relationship between the component parts, we just see less of the whole or more detail in selected element.

The lens works very differently to the eye. When we look at a scene without a camera, we have close to 180 degree peripheral vision. Wikipedia says:

The approximate field of view of an individual human eye is 95° away from the nose, 75° downward, 60° toward the nose, and 60° upward, allowing humans to have an almost 180-degree forward-facing horizontal field of view.

We are aware of objects alongside us, particularly if they are moving. But we only clearly see a very small area of the scene in front of us. Our eyes give us a wide view of the scene and we’ll choose what interests us or what we need to look at and pay attention to and we ‘zoom in’.

The 17mm only gives 93 degrees of horizontal view, but captures much my view of the park. The 200mm only shows 10 degrees and effectively captures an area I might be ‘looking at’.

The picture below is another shot at 200mm but cropped in a more interesting way with the War Memorial visible on the hill.

200mm Portait

Two more snaps taken a little later in the day as the sun began to set, show the effect again, this time using a 40mm and then 200mm lens.


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