F-stop

F-stop is a crucial aspect of photography that affects everything from exposure to depth of field.

F-stops can be a bit tricky to understand in the beginning, but they're easy to understand once you know how they interact with aperture and the rest of the exposure triangle...

What is an f-stop?

The f-stop or f-number is the ratio between the lens focal length and the entrance pupil diameter. F-stop is the number shown in your camera that indicates the changes in the lens aperture size. It’s written as the f/2.8, f/4, etc., on the screen/viewfinder.

Although some cameras may not display the “/” symbol or use a capital “F” instead, it still means the same thing.

When we say “larger f-stop,” what we mean is f/1.4, f/2, and f/2.8. But when mentioning “larger f-number,” it refers to f/11, f/16, and f/22. Check out this chart for a visual guide:

So, how do you “count” the f-stop? And what’s the meaning of “larger” and “smaller” f-stops/f-number?

Difference between smaller and larger f-stops

We have all been confused by the smaller and larger aperture concepts. Yet, the hint has been in front of us the whole time. The F in F-Stop is like a fraction.

To put it in practice, the f-stop of f/22 is equivalent to 1/22, and F/1.4 is the same as 1/1.4. Think of it as pizza slices. When you cut the pizza into half (½), you will have a larger portion than cutting it into one-eighth (⅛), right? This metaphor perfectly explains why the smaller f-stop numbers (ex. f/1.4, f/2.8, etc.) translate into a larger aperture and vice versa.

The next time your mentor asks you to use a larger aperture, you should set your f-stop to f/1.4 to f/2.8. In contrast, when he/she recommends a smaller aperture, use the f/8, f/16, and so on. But… What does the “F” even mean?

What does the "f" stand for in f-stop?

The answer is it stands for focal length. If you have a Canon EF 70-200mm f/4 lens fully zoomed in, the aperture blades' diameter will be 200mm. Then divide 200 by 4 (4 because it's the max aperture), and you'll get 50 as a result.

It means that the diameter of your aperture blades in the lens will be precisely 50mm. Using that example, we instantly know that the aperture blades will appear larger at f/1.4 and become ridiculously small at f/22.

Is it necessary to always count the diameter of the aperture blades in the lens? No, but this extended information about the camera mechanism will come in handy when you take on a professional project with rigid requirements.

Importance of aperture

Aperture will determine the focus and exposure of your image. Smaller apertures will give a photo with throughout focus from foreground to background. On the other hand, larger apertures will only focus on the foreground while blurring everything behind it.

We have a full guide on aperture if you want to check that out later. Your choices of apertures should be suitable for your photography vision. Does your concept need a specific focus? Do you want to focus on the foreground only or the whole scene?

If your concept requires a shallow focus on your subject, choose a larger aperture (f/1.4 to f/4). For landscape photography, it will be better to use smaller apertures ranging from f/8 to f/16. Reference this chart again:

A larger aperture allows more light to enter the lens and provides greater exposure. In contrast, smaller apertures let in only half the amount of light as the larger aperture.

By now, you may be wondering if the f-stop and aperture are the same thing.

Are aperture and f-stop the same thing?

Well, if you break down what f-stop is, it’s essentially the same. Most people use the terms f-stop and aperture interchangeably. But if we want to be very accurate and precise, the difference is in the definitions.

1. Firstly, the f-stop meaning is the ratio between the focal length and the aperture blade diameter (f-stop = focal length/diameter as mentioned earlier). Meanwhile, the aperture is defined as the lens entrance pupil diameter.
2. Secondly, the aperture along with shutter speed will limit how much total light can reach the sensor. The combination of total light and sensor efficiency will determine the noise in your image.

That being said, the f-stop determines the intensity/density of light that will hit the sensor which is commonly known as exposure.

The density of light can be affected by lens length and the diameter of its opening. The f-stop takes this into account, resulting in a relative aperture. The f-stop can allow the same amount of light that other lenses can (limited by the maximum aperture).

How to choose a f-stop?

As mentioned, choosing your f-stop will be highly situational.

Larger f-stops

A larger f-stop allows the image to focus on your subject/foreground while blurring the background.

Smaller f-stops

Meanwhile, the small f-stop will put both foreground and background into focus, but sacrifice the amount of exposure.

Is a higher f-stop better?

If you mean “higher” is a larger f-stop (f/1.4 and f/2), I must disagree. Having a higher f-stop helps you get as much light into the sensor as possible, but it will (again) completely blur the background.

The smaller (below f/8) f-stop will also lead you to a problem because it decreases exposure.

The final decision is coming back to you. There are many genres/niches in photography, and all of them require different f-stop settings.

For example, macro photography needs large apertures (smaller f-stops) to capture small subjects with the highest sharpness and bokeh. Landscape photographers tend to choose smaller apertures (larger f-stops) to achieve precise sharpness in the view.

When should you change your f-stop?

Changing f-stops should be done if your subject is out of focus. Remember the focal length earlier? It guides us to change our focus and f-stop whenever the subject moves forward or backward.

It would help to change your f-stop whenever your photo is under-exposed or overexposed.

When vignette (edges in photo getting disproportionally darker), diffraction (basically images becoming less sharp the smaller your f-stop is), and chromatic aberration trouble you, it means that your f-stop is too small. Hence, it’s time to change the f-stop.

You should have already learned a lot about f-stops by now. This very flexible and functional feature can be tailored to every need. Oh, and don’t forget to keep practicing to get a better experience of the f-stop mechanism. Good luck!