Aperture Numbers Explained: How To Stop Making Little Mistakes

Are you ready to have aperture numbers explained in a way that you will actually understand and be able to use when taking photos? After all, learning photography isn't easy. Too, f-stops or aperture numbers are really not intuitive. Therefore, they're really hard to get right when you're also trying to focus on your subject, make sure nobody is photo-bombing you, etc. 

Aperture Numbers Explained

Aperture, if you didn't know, is the opening in your lens that lets the light in. This opening is typically controllable. In other words the number itself can be changed. We can open it larger to allow more light in, or close it to let in less light.

That bit is simple. Right?

Halving and Doubling

Each time we adjust our aperture number we're doubling or cutting in half the amount of light. This is also fairly simple to understand. However, the difficulty comes with remembering how to make adjustments to our aperture when we're actually out there taking real photos.

Also, aperture numbers get larger when the opening gets smaller. As a result, it can be doubly confusing.

Aperture Number/F-stop List

The standard range of aperture numbers are as follows:

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, and 22

1.4 lets in the most light (in that series) and 22 lets in the least. It's getting less simple now.

Other f-numbers

There are sometimes bigger and smaller numbers as well (like f.95 and f1.2, or f32 and f45). Plus, many lenses have 1/2 or 1/3rd f-stops. This is great when you know what you're doing but not great for learning because it's more confusing.

Finally, many lenses included in kits with your camera start at a 1/2 f-number. A great example of this is lenses where the biggest aperture is f3.5.

Are you more or less confused at this point? I hope you're less confused but don't feel bad if you're more confused. This stuff isn't easy. Consider taking a photography class where an instructor can explain it and you can ask questions.

The Aperture Number Pattern Explained

Look at the f-numbers. Notice anything interesting? If not then look at every other number. For example, 2, 4, 8, and 16. These numbers are double the number before them. However they have numbers between them. Why is that?

Aperture numbers double or divide in half the amount of light.

Our lenses are circular in shape. Therefore, the number needs to half or double the diameter of the numbers on either side of it. After all, we're dealing with Pi and squared radii because of those circular lenses.

Half the diameter of 4 is 2.8. Ultimately, it comes down to square roots but you're not ready for that bit yet. So, first let's talk about fractions.

Aperture Numbers Are Fractions

Very few people like fractions. That's because very few people understand fractions (in practice).

We use the term f-stop to refer to these f-numbers, aka aperture numbers (so many names).

Therefore, it can be tempting to think that the f in f-stop means fraction. To be honest, you can tell yourself that if it helps. However, the f actually stands for focal length. Again though, seriously, pretend it stands for fractions. It will make your life easier.

Read to the end of the article if you really want to nerd out on how we calculate f-numbers. 

Fractions Suck

Everyone agrees that fractions suck. They're unnatural, abominations! Amounts that are smaller with numbers that are bigger??? Blasphemy!!!

Of course, fractions are a super important part of photography. We use fractions of a second to set our shutter speed. So too, fractions are a part of our aperture numbers.

We're Stuck With Them

When it comes to aperture numbers it's important to remember that the bigger the number the smaller the opening. This is because those numbers are really the denominator (i.e. the bottom number in a fraction).

An alternative to remembering that bigger number means smaller hole is to remember that bigger number means less light. So, if you want your photos to be darker then it makes sense to use a bigger f-number. Also the opposite is true.

No matter which way you choose it can be really helpful to picture our f-numbers as fractions. It's 100% technically incorrect to see them as 1/f-number. That said, if that helps you remember that they're a fraction, go ahead and do so.

An Easy Explanation for Aperture Numbers

An easy explanation for aperture numbers doesn't exist. After all it's math. Plus, we're dealing with circles and adjusting the amount of light by doubling it or cutting it in half. There's nothing easy about doing that. Why in the world would you think there is?

That said, there is always memorization. Look at your lens. What is the biggest number it has on it? This is often f22. Remember that this number lets in the least amount of light.

Now, which is the smallest number? Whatever that number is, remember that it allows in the most light.

Aperture And Depth Of Field

Our aperture not only controls the amount of light we let in. It also controls the amount of our scene that appears to be in focus behind and in front of what we're actually focused on. The bigger the opening of our aperture the less stuff appears in focus related to what we've actually focused on.

Depth of Field is not an easy concept. Therefore, let's forget it for now and focus just on understanding aperture's impact on the light we allow into our cameras.

Making Sense of Aperture Numbers

Aperture numbers eventually will make sense to you. Of course, that requires you to practice photography often enough that you don't forget between sessions.

If you want a real deep dive into how f-numbers work then keep reading. However, if you think it might confuse you more stop here! No shame, really. This stuff is hard. Take a break. Touch grass. Go take some photos.

I've included the information below because a lot of people learn better when they know how things work to the degree covered below. That said, if you're not one of those people feel free to read this article on aperture priority. Then, put your camera on aperture priority and get a feel for those aperture numbers.

Aperture Numbers and Focal Length

The focal length of our lenses are usually marked in millimeters. You've likely heard of 50mm lenses or 35mm lenses. The f in f-stop is the focal length. To get the aperture number we use a formula wherein the aperture diameter is equal to the focal length over the f-number.

What does that mean? Let's take a 50mm lens for example. If our lens opens up to f2 then we can take the focal length 50 and divide it by the f-number. In this case it's 2. 50 divided by 2 is equal to 25. So, f2 on a 50mm lens is an opening of 25mm.

Still Here And Ready For More?

The 50mm example seems easy enough. Too, it helps us to understand why we don't have many 400mm lenses that open to f2. After all, they'd need an aperture that opens to a diameter of 200mm or 20cm.

If you're from the US (like me) 20cm is nearly 8 inches.

Square Roots Have Entered The Chat

F-numbers can be memorized.

Too, they're always going to be the same. Only the range of what is available will change. Our goal of increasing or decreasing the amount of light by a factor of 2 requires us to use the square root of the current aperture number. Remember, we're doubling or halving the amount of light (not the number itself).

If we want double the amount of light from f2 then we need to multiple by the square root of 2 which is 1.4. That means we get 1.4. If we want to double the amount of light again then we get 1.2.

Forget The Square Roots And Fractions

Honestly, you shouldn't worry about remembering square roots and fractions and all of this. Instead, just remember that when you change your f-number by an entire f-stop then you've doubled or halved the amount of light.

Questions? Contact me.