Aperture f/1.8, f/1.4: what this number means on a camera

The aperture is the opening in the lens through which light reaches the sensor. It is written as an f-number: f/1.4, f/1.8, f/2.4. The smaller the number, the wider the opening and the more light gets through.

The aperture works like the pupil of an eye

In plain words

The aperture is like the pupil of your eye. In the dark, the pupil widens to let in more light; in sunlight, it narrows. The f-number is like "pupil size in reverse": f/1.4 is a wide-open eye, f/4 a squint. A wider aperture means brighter night photos and more background blur.

How it works

Light passes through the lenses and the aperture opening.
The f-number is the ratio of the focal length to the diameter of the opening.
f/1.4 lets in roughly twice as much light as f/2.0.
A wider aperture gives a shallower depth of field, so the background blurs more.
Most smartphones have a fixed aperture; only a few have a variable one.

A wider aperture means more background blur

Where you'll see it

In the specs of every phone camera: "50 MP, f/1.7". Flagship main cameras have f/1.4-f/1.9, ultra-wides f/2.0-f/2.4 and telephotos f/2.4-f/3.5. Some flagships have a mechanical variable aperture.

Does it matter when buying

As part of the picture, yes. A brighter aperture helps at night, but sensor size matters more: a big sensor at f/1.9 often gathers more light than a small one at f/1.6. So compare cameras as a whole - or better still, compare real night photos.

Myths

Myth: f/1.6 is always better than f/1.8. Reality: Only with the same sensor. Compare together with sensor size.
Myth: A smaller f-number is a bigger setting. Reality: The opposite: a smaller number means a wider opening.

FAQ

Why does a smaller number mean more light?

Because it is a fraction: f/1.4 is the focal length divided by 1.4, so the opening is relatively bigger.

What is a variable aperture?

A mechanism that lets the camera narrow the opening for sharper focus across the whole frame.

Does aperture affect portrait mode?

It affects natural blur, but on smartphones software often enhances it.