Exercise: Focus at different apertures
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As I discussed in the exercise 'Getting to know you camera', the aperture can change the depth of field for a given scene. When the f-stop is lower the aperture will be wider, resulting in photographs where the image subject is in focus and the surrounding details are blurred. Conversely, a higher f-stop (narrower aperture) will produce images will a greater depth of field, capturing surrounding details in greater clarity.
Logically, when the aperture is wide it will allow more light to reach the sensor when capturing the image; when the aperture is narrow it will let less light through. It is simplest to think of the aperture as the pupil of an eye. When the pupil is dilated it allows more light to reach the back of the eye and vice versa.
Also to note, different apertures will require the shutter speed to compensate for the amount of light allowed through to produce the optimum exposure.
This exercise requires a scene with depth to be taken at an acute angle. The same picture will be shot x3 times, each with a different size aperture to measure the resulting blur around the focus point. A game of pool inspired the subject matter for this exercise, so I set the camera up on a tripod and focused on the 8-ball (naturally). I took x3 photographs; the first at the camera's widest aperture; second at it's narrowest; third somewhere in the middle.
#1 - f4.2
As it is evident, the wide aperture has caught the in-focus 8-ball crisply and blurred the surrounding spot & stripes. The balls immediately around the 8-ball appear fuzzy and the balls at the furthest reaches of the fore and background are so out-of-focus that you cannot make out their respective numbers.
#2 - f22
At the narrowest aperture the photo now captures the surrounding details in greater clarity. The surrounding balls are in-focus and the numbering can be made out.
This exercise has shown that I will have to pay greater attention to the aperture size when photographing. Perhaps I will want a scene with reduced depth of field, maybe when photographing a friend and it is more important to focus on them rather than the background? Another possibility in a very narrow aperture when photographing landscapes and capturing all the detail. Much to consider.
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