So what is aperture? Aperture, more commonly called f-stop, is defined as the size of the opening
in the camera's lens. The wider the opening, the more light that is able to reach the sensor. In contrast, a smaller opening allows less light to reach the image sensor.
But aperture is not just a light setting! A wider opening doesn't only mean more light but also more background blur. And in turn, the smaller the opening, the less that background will blur in the photograph.
As a test, I took three photos, all at different apertures. The first photo at f5.6 shows a lot of
background blur. The second at f13 reveals a smaller amount of blur than is present in the first photo.
But in the last image at f36, you can see that the least amount of bokeh (background blur) appears
due to the smaller size of the aperture.
f5.6
f13
f36
One more detail that might be good to note: lenses are made so that the best image quality comes from a mid-range f-stop, about f11-16. So, if background blur is not an issue in the shot, you might want to consider using these f-stops for best results.
