Aperture

The aperture is a part that is located inside every camera lens. As a changeable hole, the aperture regulates how much light the lens passes into the camera when taking a picture.

The aperture and lens diaphragm are constructed of several various metal blades depending on the lens characteristics and your camera settings move and regulate the size of the aperture and the amount of light being let through.

The value and size of the aperture are measured in f-numbers and/or f-stops, f/

How large the aperture is, is measured with a number and value. This is written with f/. Perhaps you have looked at a camera lens product name and wondered what the underlined numbers really mean?

Canon EF-S 18-55mm f/3,5-5,6 IS"

Slowly we will now get to know these f-numbers and let's start by saying:

A large aperture, that allows a lot of light to pass into the camera, has a low f-number.
A small aperture, that does not allow that much light into the camera, has a high f-number.

It does sound confusing, right? Ok, let's take it one more time.

A large aperture, that allows a lot of light to pass into the camera, has a low f-number.
A small aperture, that does not allow that much light into the camera, has a high f-number..

Example of different aperture values and f-numbers

Common values of the f-number scale are:

f/1,2 (very large opening, allowing a lot of light)
f/1,4
f/1,8
f/2
f/2,8
f/4
f/5,6
f/8
f/11
f/16
f/22
f/32 (very small opening, not allowing that much light)

How does it look like when the aperture is changing its shape and value?

The video clip below illustrates how the aperture is being adjusted inside the lens.

If a camera lens is called "Canon EF-S 18-55mm f/3,5-5,6", what f-number does it have?

From the camera lens specifications and product name it is possible to identify that it is a zoom lens.
18 mm focal length at the maximum wide-angle end.
55 mm focal length at the maximum zoomed-in setting.

When you look at a product name of a camera lens the aperture values displayed are always the largest and brightest ones available, to show you how much natural light the camera lens can have and allow.

When we then look at these numbers, from 3,5 to 5,6, that means that the lens has a variable aperture, where the f-number and maximum aperture value change when you zoom in and out.

Aperture value at 18 mm: f/3,5
Aperture value at 55 mm: f/5,6

The F-number is higher at full zoom and the lens can not allow that much natural light. If you see that the camera lens has a variable or constant aperture is an important factor to consider when buying your next camera lens.

If a camera lens is called "Nikon AF-S 70-200mm f/2,8 G IF-ED VR", what f-number does it have?

From the above specification you can see that this lens is a zoom lens.

70 mm focal length at the maximum zoomed-out, wide end.
200 mm focal length at the maximum zoomed-in setting (telephoto).

When we then look at the other figures we find only 2,8. which means that the lens has a constant maximum aperture value and natural light, no matter how much you zoom in or out.

Aperture value at 70 mm: f/2,8
Aperture value at 200 mm: f/2,8

Comparing aperture and brightness

See these three examples:

1. Canon EF 75-300mm f/4-5,6 III USM
2. Canon EF 70-200mm f/2,8 L USM
3. Canon EF 70-200mm f/4,0 L IS USM

These are three lenses with similar product names. They are all telephoto zoom lenses that give you a photographer a focal length of 70-200mm and 75-300mm.

Starting to look more closely at the product names you will see that the aperture values and the ability to let through light varies a lot between the three of them.

Lens 1. Canon EF 75-300mm f/4-5,6 III USM

When you zoom in with this lens at the maximum aperture, it aperture value and light ability will eventually be reduced to f/5,6.
Understanding Variable Aperture in Camera Lenses

Lens 2. Canon EF 70-200mm f/2,8 L USM

This lens has a constant maximum aperture value of f/2,8 through the entire zoom range.

Lens 3. Canon EF 70-200mm f/4,0 L IS USM

This lens has a constant aperture of f/4.

Are the f-numbers comparable on all lenses?

Yes. No matter what manufacturer of the lens, the specified f-number and aperture values all have the same characteristics. For example, if you are choosing between buying a lens from Nikon or Tamron an aperture value of f/4 will mean the same thing for both of them.

Worth noticing is that a lens with f/4 belonging to a sports photographer at a World Cup final in football/soccer has the same ability to let natural light into the camera as your lower-priced lens. This is even if his or her lens weighs several pounds and looks like a telescope. The aperture values are measured the same, other properties such as the lens focal length, image and build quality can of course make them look different and cost more or less.