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How to Easily Understand the F-stop Scale in Photography

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One of the basic terms you need to be aware of in photography is the ‘F-stop’ also called ‘F-number’.

Understanding how it works is key to achieving the correct exposure for beautiful pictures.

Don’t worry; our article will give you all the f-stop know-how. You just have to put it into practice.

Closeup of changing f-stop on a DSLR camera

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What Is the F-Stop on a Camera?

Before we would jump right into it, it’s essential to understand how the aperture works. To keep it short, the aperture blades, also known as a diaphragm in your lens work just like the pupil of the human eye. In low light, the pupil is larger, letting in as much light as possible. The same goes for your camera’s aperture.

But why is it so important? Because the F-stop scale is what helps you to measure and understand the aperture size.

On your camera, you’ll see ‘f/’ or ‘f’ followed by a number which denotes how wide the aperture is. The lower the number, the wider the aperture. You can adjust these settings in aperture priority and manual modes in your camera.

This may seem confusing: Why a low number for the maximum aperture? The answer is simple, but first, you need to know the f-stops scale as follows:

  • f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.

At this point, things get a little bit complicated and somewhat mathematical.

lizard resting on a stop sign

What Does the ‘F’ stand for in F-Stop?

The ‘f’ stands for focal length. The number following it is a fraction of the focal length. So to calculate the size of your aperture at a certain f-stop you have to divide the focal length by the fraction. For example, if you are shooting with a 200mm lens at f/4 the diameter of the aperture is 50mm.

Here are a couple of f-stop settings examples:

  • A 50mm lens with the aperture of f/2 = a lens opening 25mm wide (50mm/2).
  • A 50mm lens, with the aperture of f/8 = a lens opening 6.25mm wide (50mm/8).

This is what the aperture scale looks like (not to scale):

Aperture sizes at certain fstop settings

How the F-stop Affects Your Image

The most important thing to know about these f-stop numbers is that, from each number to the next, the aperture decreases to half its size.

If you are changing from f/2 to f/2.8, you are halving the exposure. In doing so, you’re halving the open area of the aperture in the lens. By this, you are allowing 50% less light through the lens (1 f-stop). This is because the f-stop numbers come from an equation used to work out the size of the aperture from the focal length of the lens.

Let’s say you are photographing portraits of someone at the beach during sunset. As the sun keeps going down, you will have less and less light which you need to compensate somehow. One of the possible solutions is to open up your aperture, letting in more light through the lens onto your camera’s sensor. Jumping up an f-stop will brighten up your image but also cause a change in the depth of field.

If you are shooting with a wider aperture such as f/2.8 you will notice that the area of focus is much smaller than if you were using a bigger f-stop, for example, f/5.6 or f/8. So to put it this way: The wider the aperture is, the shallower the depth of field.

You can get very creative with adjusting your f-stops for a different depth of field, but you also need to be aware of how to do it properly.

A wide aperture can easily make your picture to be blurry in undesirable areas. Especially in portraits where if you use a very small f-stop such as f/1.8, your subject’s nose could be out of focus while their eyes are still sharp. So, in this case, the area of focus can be less than 10mm, which is a very shallow depth of field.

Close up image of a girl's eye with a very shallow depth of field

Narrower apertures (f/8, f/11, f/16, f/22) are mostly used for landscape photography as they result in a bigger area of focus, keeping most of the environment sharp. However, as explained earlier, these f-stops don’t let as much light in as wider ones, so your shot can come out underexposed.

All lenses have a limit of how wide their apertures can be opened, these usually are the following f-stops: f/1.4, f/1.8, f/2.8, f/3.5 f/4 f/5.6.

In some cases, the focal length of your lens can affect the smallest f-stop you can use. Some zoom lenses don’t come with variable aperture and the lowest f-stop you can use depends on the focal length you are using your lens with. Here’s an example:

A 70-200mm variable aperture lens can produce the lowest aperture at 70mm. Once you zoom in to 200mm your aperture will automatically set itself to f/5.6 or something like this. These lenses are usually cheaper than fixed aperture zoom or prime lenses. A prime lens is when the focal length is not adjustable. A lot of professional photographers tend to use prime lenses as they usually can produce a much wider aperture opening.

What happens when you use the widest possible aperture of your lens, but there’s still not as much light as you need? Your image will be underexposed and you have two options to correct it. Either you manage to get an additional light source, or you can adjust further settings in your camera other than the aperture.

Understanding the Exposure Triangle

Exposure is made from three settings, which make up the exposure triangle. These are the shutter speed, ISO and aperture settings.

As your photography skills improve, you will start to shoot in manual mode more. You will gain more control over how the camera exposes the scene. Knowing what exposure stops can do for the shutter speed, ISO and aperture will affect how you change each one.

Shutter Speed and ISO Stops

Apart from the aperture f-stop scale, we can also measure the ISO and shutter speed in stops. The same concept works here with a small difference. At ISO and shutter speed, a whole stop is always doubling or halving each value.

Another difference from the aperture f-stops is that ISO and shutter speed does not have any effect on the depth of field. Although by adjusting these two settings on your camera, you can control how much light your image will have.

Apart from controlling the exposure, ISO and shutter speed have other effects on your shot.

ISO Stops

Let’s start with the easiest to understand: ISO. One-stop up from ISO 100 is 200. And one-stop up from ISO 200 is 400.

The intervals aren’t equal but, instead, the ISO doubles between stops. Easy enough to understand, so I’ll leave it at that.

Be careful though, the bigger you set the ISO the more noise your image will have! Why? Because what raising the ISO does is that it makes the sensor of your camera more sensitive to light. The camera does this with an increased electric charge and the noise on the shot is the by-product of this adjustment.

Although you should not be afraid of stepping up your ISO. This can help you to be more flexible with adjusting shutter speed and aperture to achieve different ‘effects’ in your for your photo. For example, if don’t have that much light and your aperture is also as wide open as possible, adding some ISO can help you to expose your shot correctly.

Shutter Speed Stops

The majority of the time when you use your digital camera, you’re shooting at a fraction of a second. If you shoot at speeds of 1 second or longer, the same principle as above applies. You double the time from 1 second to 2, then from 2 seconds to 4. Simple.

When shooting at a fraction of a second, such as 1/200, to double this number, halve the denominator (the number on the bottom of the fraction, in this case, 200).

If you’re new to photography, don’t worry; this will soon become second nature.

1/100 is twice the length of 1/200 so that’s one-stop and the exposure is doubled. 1/50 is twice the length as 1/100 and so on.

Cityscape at night

Let me make this simpler for you:

You’re shooting at f/2.8, at 1/100 of a second, with an ISO of 200 but you want a very shallow depth of field. You know that widening your aperture opening to f/2.0 will produce a shallower depth of field.

Perfect! But it will also triple the amount of light that’s entering your camera lens. You have jumped up two f-stops with your aperture and made the exposure brighter.

You need to counter this with a change in shutter speed or ISO. To do this, you can halve the ISO to 100 or double the shutter speed from 1/100 to 1/200 of a second.

So you see, this is quite important to know.

Blurry field with a castle in the background


To summarise, increasing the exposure by one-stop will double the exposure and decreasing the exposure by a one-stop will halve it.

But wait, there’s more!

With your aperture, shutter speed, and ISO, there are more intervals than just doubling and halving exposures. For example, between f/1.4 and f/2, you will also find another f-stop, f/1.8. These are third stops, which give you more control over your exposure.

I hope this article was helpful for you, and now you understand how the f-stop scale works better than ever. Now it’s time to go out there and put everything you learned in practice.

Check out our post on understanding the difference between a t-stop and f-stop next.

If you’re just starting out and want to expand your knowledge, sign up for our Photography for Beginners course today!

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