Large apertures (small numbers) let in more light.
So here goes, I’ve kept it as brief as possible and I hope I’ve made it clear!!
The aperture is the size of the lens opening which can be adjusted either manually or automatically by the camera to adjust the amount of light passing through the lens.
The graphic on the left shows typical aperture values or f-stops and the relative opening size. The particular values shown double or halve the amount of light with each step.
Note that large apertures which let in lots of light have small numbers, I won’t bore you with the reason why, it’s just the way it is.
The shutter speed is the amount of time, usually a fraction of a second, for which the shutter is open and casting light on the sensor and, confusingly, this might be shown as a whole number even though it’s usually a fraction of a second. For example, 1/20th of a second might just be shown as 20.
a slow shutter speed to create motion blur. Photo by Henri Cartier-Bresson
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These two parameters work together to create the exposure, a certain amount of light for a certain amount of time. We can, if we wish, change the value of one of these parameters and compensate by changing the value of the other one, thereby keeping the exposure the same.
For example -
If we double the amount of light by changing the aperture from f11 to f8 and at the same time halve the length of time of the exposure by changing the shutter speed from 1/50th of a second to 1/100th the exposure will remain the same.
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So why does this all matter?
Choosing a large aperture will blur our background, ideal for portraits. Or a much smaller aperture will tend to keep the background in focus, perfect for landscapes and interiors.
Conversely we can set a fast shutter speed (maybe 1/500th of a second) to freeze movement such as sport, or chose a slow shutter speed such as a 1/50th to show movement blur while being a little more creative.
The magnificent photograph of the sculptor Alberto Giacometti is a wonderful example of the photographer choosing a slow shutter speed to blur the moving primary subject while the static sculptures in the foreground and background remain sharp. The physical and emotional beauty of his work is undiminished and the artists impetuous temperament is beautifully communicated.
Maybe he is smoking two cigarettes!
With the cameras Mode Dial set appropriately whichever setting you change, be it the aperture or the shutter speed, the camera’s automatic exposure system will compensate by adjusting the other parameter.
A large aperture blurs a distracting background
A short photography course from your local professional will enable you to take control of these settings and open up the wonderful world of creative photography that exists beyond the auto setting.
