Aperture is one of the three pillars of photography, the other two being ISO and Shutter Speed. Without a doubt, it is the most talked about subject, because aperture either adds a dimension to a photograph by blurring the background, or magically brings everything in focus.
1) What is Aperture?
When you hit the shutter release button to take a picture, a hole in the lens opens up to allow light to hit the image sensor. The size of that hole is called the “aperture”.
Aperture is the maximum size of the lens opening when the shutter is released.
The larger the opening in the lens, the more light that hits the image sensor.
The smaller the opening in the lens, the less light that hits the image sensor.
Aperture is measured in “f-stops”. Increasing the aperture by a full stop doubles the amount of light entering the lens, while decreasing the aperture by a full stop halves the amount of light entering the lens. These full stop aperture measures are as follows:
f/1.4 … f/2 … f/2.8 … f/4 … f/5.6 … f/8 … f/11 … f/16 … f/22 … f/32
These numbers actually represent fractions, therefore the bigger the number the SMALLER the aperture. As such, f/22 represents a very small lens opening (SMALL aperture) while f/1.4 represents a very large lens opening (LARGE aperture)
Therefore, as you move one stop up the scale, say from f/5.6 to f/8 (DECREASING the aperture), you are decreasing the exposure by one stop. Conversely, as you move down the scale, say from f/22 to f/16 (INCREASING the aperture), you are increasing the exposure by one stop. Also, many of today’s digital SLR cameras graduate the aperture setting by 1/3rd stops, allowing greater control over exposure. This therefore means that if you wanted a full stop change in aperture, you would turn the aperture dial three “clicks”.
Putting it simply,
Larger the number = the smaller the aperture = less light = decreased exposure
Smaller the number = the larger the aperture = more light = increased exposure
3) What is Depth of Field?
One important thing to remember here, the size of the aperture has a direct impact on the depth of field, which is the area of the image that appears sharp. A large f-number such as f/32, (which means a smaller aperture) will bring all foreground and background objects in focus, while a small f-number such as f/1.4 will isolate the foreground from the background by making the foreground objects sharp and the background blurry
As you can see, just changing the aperture from f/2.8 to f/8.0 has a big effect on how much of WALL-E is in focus and how visible the background gets. If I had used a much smaller aperture such as f/32 in this shot, the background would be as visible as WALL-E.
In the above example, due to the shallow depth of field, only the word “Cougar” appears sharp, while everything else in the front and behind of that word is blurred. If I had used a larger aperture such as f/1.4 and focused on one of the letters, probably only that letter would have been sharp, while everything else would have been blurred out. The larger the aperture, the smaller the area in focus (depth of field).
4) Lens Apertures: Maximum and Minimum
Every lens has a limit on how large or how small the aperture can get. If you take a look at the specifications of your lens, it should say what the maximum (lowest f-number) and minimum apertures (highest f-number) of your lens are. The maximum aperture of the lens is much more important than the minimum, because it shows the speed of the lens. A lens that has an aperture of f/1.2 or f/1.4 as the maximum aperture is considered to be a fast lens, because it can pass through more light than, for example, a lens with a maximum aperture of f/4.0. That’s why lenses with large apertures are better suited for low light photography.