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Last updated on November 8th, 2020

“Light turns the ordinary into the magical”

Trente Parke

Light is what makes a photograph, whether by its presence or its absence.

No photographer can get the desired image unless they understand the light that reaches the camera sensor, both the quantity and the quality. 

While the quality of light is subjective and left to the audience for their judgment, the quantity is something over which the photographer has complete control.

This fundamental principle is what makes understanding aperture important in photography. Being able to control aperture and understand its effects on the final image will allow you to control light itself and create the perfect composition.

Let us have a look at what aperture means and what you can do with it.

Meaning of Aperture in Photography

In simple terms, aperture refers to the ‘opening’ of your lens, the hole through which light enters and travels up to the image sensor. It is one of the three factors — along with shutter speed and ISO — which decide how your photo will look.

If you imagine a vintage pinhole camera, the aperture is actually the hole itself, and acts as the entrance for light.

Without an aperture, there is no door for the light to come through, and thus there can be no image. With a large aperture, there’s a lot of light coming in.

In photographic terms, the aperture is a characteristic of the lens and can change. It is denoted by an f-number or f-stop, for example, f/2, f/5.6, f/8, etc. 

We’ll learn more about how these numbers affect the quantity of light after a short biology lesson.

front of lens aperture

How Does Aperture Work?

To understand how aperture works and why it impacts your image in massive ways, you need to understand the world’s most advanced camera — the human eye.

Even our eyes have their own biological aperture called the ‘pupil.’ That’s right.

The small black spot in the middle of our eyes is the human aperture and keeps changing in size, depending on our surroundings. In bright light, the pupils automatically shrink — which is the same as reducing the aperture — to let in less light.

The next time you squint your eyes in the middle of summer, remember that your eyes are adjusting their aperture and allowing you to see clearly. Without that squint, the whole scene would be bright and overexposed.

Camera lenses follow the same mechanism. The metering sensor will automatically adjust the aperture, shutter speed, and ISO to ensure that the photo does not turn out too bright or too dark.

How Are F-numbers Related to Aperture?

You would have noticed numbers like f/3.5 and f/8 on your lens and your viewfinder when taking a photo. That is a representation of the aperture.

Because of the manner in which lenses are constructed, the size of the aperture — or the diameter of the hole — often changes with focal length. 

For example, a 50 mm f/2.8 prime lens has a focal length of 50 mm, and an f-number of 2.8, while a 100 mm telephoto lens might come with an f-number of f/4.5.

Where did this 2.8 and 4.5 come from?

For a particular focal length, the lens’ hole can open only up to a few millimeters. When you divide this focal length with the aperture diameter, you get the f-number.

Consequently, a 50 mm f/2.8 lens implies that the diameter of the opening must have been around 18 mm. Conversely, when the 100 mm lens was constructed, and it was noticed that the aperture was about 22 mm, the f-number had to be f/4.5.

Despite the algebra involved, you should try to understand this ‘inverse’ relation. The higher the f-number, the smaller the aperture. This means that on a late evening when you are trying to open up the aperture to let in more light, you will have to select a lower number like f/3.5 or f/2.8.

Let us discuss how to control the aperture.

aperture size examples