Focusing With Different Apertures

As with the exercise for focusing with a fixed aperture, for this exercise another scene was selected which had depth.

Placing the camera on a small tripod, the central focus point was positioned on the fifth wheel in the row of bicycles, approximately in the center of the image and the camera was set to aperture priority. Images were taken at different stops of the aperture scale. The images below show the results of the widest aperture, a mid-range aperture and the narrowest aperture:

Wide Aperture - f1.8

At the widest aperture, the area of focus is very narrow and the only parts of the image that appeared in focus are the last bike light and the next wheel.

Middle Aperture - f8

Using a mid range aperture, the focus area has clearly extended based around the center point. All tires other than the very closest are now in focus (you can see the tread patterns) and at the back of the picture, focues appears to be falling away at the glass wall at the back of the image.

Narrow Aperture - f22

Selecting the narrowest aperture, the Focus area again can be seen to have extended as the front tread pattern is now visible, however, looking at the building in the background, focus appears to have been lost slightly. This could be described as the imaging appearing softer.

The apparent softening of the image is generally unexpected when comparing images taken with a narrower aperture, however, there is a technical feature which can become apparent when narrowing apertures known as diffraction as discribed here. The reason I believe this to be a demonstration of diffraction limitations is that looking at an image taken at f16, the image appears to be sharp all the way through the image:

Narrow Aperture - f16


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