What is F-Stop? | Photography Definition, Tips, and Examples

What is 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, and so on in the screen/viewfinder
Although some cameras may not display the “/” symbol or use a capital “F” instead, it still means the same thing. Some cameras will also provide smaller f-stop numbers such as f/1.4 or f/22. 
When we say “larger f-stop,” what we mean is f/1.4, f/2, and f/2.8. But when mention “larger f-number,” it refers to f/11, f/16, and f/22.
So, how do you “count” the f-stop? And what’s the meaning of “larger” and “smaller” f-stops/f-number?

aperture f stop
Photo by Steve Johnson

Smaller and Larger F-Stop

We have all been confused with the smaller and larger aperture concept. 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, F/1.4 is the same as 1/1.4. Think of it as pizza slices. When you cut the pizza into a 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 (1, 2, 3, and 4) translates 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?

f stop aperture size
Photo by Pixabay

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 in the f/1.4 and becoming 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 a professional project with rigid requirements. 

f stop aperture light
Photo by Terje Sollie

Why Aperture is Important?

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.

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.

A larger aperture will allow more light to enter the lens and provide greater exposure. In contrast, smaller apertures will only let in half the amount of light than the larger aperture.

For example, an f/2.0 f-stop will allow 800 lumens into the sensor, while the f/2.8 only lets half of the original amount (400 lumens) touch the sensor.

But what is the best setting for macro photography when you want a vivid background? In this situation, your saving grace is bracketing and stacking. Read our dedicated bracketing article for more information.

By now you may wonder, is the f-stop and aperture the same thing?

bokeh aperture
Photo by Kat Jayne

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.

Firstly, the f-stop meaning is the ratio between the focal length and the aperture blade diameter (f-stop = focal length/diameter). Meanwhile, the aperture is defined as the lens entrance pupil diameter.

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 that 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 do I Choose an F-Stop?

Well, like I’ve said before, choosing your f-stop will be highly situational. 
A larger f-stop allows the image to focus on your subject/foreground while blurring the background. Meanwhile the small f-stop will put both foreground and background into focus, but sacrificing the amount of exposure

Now let’s get a bit technical to make it clear.

  • When the lens is in focus, the image/videos’ sharpness won’t be affected if you move the camera to the left or right. But, if you move it forwards or backward, the image/video will be blurry. 
  • ISO helps neutralize the exposure when you use the smaller f-stop. Set the camera to the manual mode when you have a firm understanding of how both these settings and shutter speed work together.
  • The sharpness of the image will also depend on the picture’s dimension and megapixel size. A landscape picture may look fine in a 4 x 6. But when you blow it to 10×20, you’ll see some parts are out of focus. 
  • In theory, everything between the minimal and hyper-focus should appear sharp. In reality, if you try to get the focus on your subject manually, you will get a better and more precise result. 
  • The depth of field calculator has interesting information that might help you during the photo session. But from my experience, it’s better not to use it.
  • The sweet-spot for most f-stops would be the medium numbers which are f/2.8, f/4, and f/5.6. Try to do some experiments around these numbers to see which one suits your vision the best. 
  • Chromatic aberration will appear when you shoot a scene with high contrast. To avoid this, use a smaller f-stop or fix it in post-production using Adobe Lightroom or Photoshop editing software. 

In summary, the easiest way to decide the f-stop number is by taking some test-shots. Take test-shots starting from the largest to the smallest f-stop until your subjects are in focus. 
Don’t sweat about chromatic aberrations and vignettes because we can easily fix them in post-production. Prioritize to get the right sharpness and exposure.

fstop focal length
Photo by Pixabay

Is the Higher F-Stop Better?

If what you mean by “higher” is a larger f-stop (f/1.4 and f/2), I must disagree. Because having a higher f-stop does help 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 the exposure.

The better option is to hover around the middle f-stop such as f/2.8, f/4, f/5.6. It will provide enough sharpness for both your subject and its background. Exposure levels will also be just right since it doesn’t allow too much or too little light.

Even so, the final decision is coming back to you. There are many genres in photography, and all of them require different f-stops settings.

For example, macro photography needs large apertures to capture the small subjects with the highest sharpness. Landscape photographers tend to choose smaller f-stops to get a 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 about the focal length earlier? It guides us to change our focus and f-stop whenever the subject moves forwards or backward.

It would help if you also changed 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 indicating it’s time to change the f-stop.

Final Remarks

Let’s wrap this up:

  • F-stop is a number based on your aperture. The numbers are fractions, making f/1.4 larger than f/22.
  • “F” stands for focal length, which means the diameter of the camera’s aperture blades.
  • Aperture helps you control the brightness/exposure and depth of field of your photos.
  • F-stop and aperture are essentially the same but different in the little details.
  • Choose your f-stop depending on the conditions, concept, and subject.
  • Although photographers commonly use higher/larger f-stops, the better option is using the medium f-stop. 
  • The best way to find the right settings is by taking some test-shots at different f-stops. 
  • Change your f-stop whenever your subject moves front/backward or when an unwanted blur appears.

At this point, you should have already learned a lot about f-stops. This very flexible and functional feature can be tailored for every need.

Oh, and don’t forget to keep practicing to get a better experience of the f-stop mechanism. Good luck!

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