PHLEARN MagazineF-Stops: Everything You Need to Know

F-Stops: Everything You Need to Know

When we’re talking photography, the f-stop has got to be one of your first stops. To be honest, when I first started learning about photography, the f-stop nearly scared me off. I’m not a math person, and the concept felt too counterintuitive. I can promise you, however, that, once you’ve wrapped your head around the concept, it’s a cinch. Coming from a non-math person, that means a lot.

Let’s start with a pretty photo to illustrate our topic.

This shot gets us up-close and personal with our topic: The f-stop. In it, you can spot two features that’ll help you understand what an f-stop is:

  1. The aperture – the small hole at the back of the camera’s lens. This hole lets light travel through the lens. The f-number (also known as the focal ratio, f-ratio, or the f-stop) is the word we use when we’re measuring the aperture’s diameter.
  2. The aperture blades open and close to make the aperture larger or smaller, according to your focal length adjustments.

You’ll want to use your f-stop for two things:

  1. Adjusting the amount of light in your photo.
  2. Adjusting the amount of clarity or blur present in your photo (the depth of field).

It’s important to note that f-stop calculations are made for you when your camera is in automatic mode. However, in this mode, your camera adjusts the f-number with mathematical, not artistic, intelligence.

For example, imagine you’ve been asked to take photos at a friend’s recent graduation. For one shot, you’ve decided to snap a candid photo of your friend during the ceremony. Since there are other grads standing nearby, they are in the shot; however, you’d really like to focus on your friend (you’re there to capture their moment, after all). If you’ve opted to shoot the scene in automatic mode, the camera may make calculations that cause the camera to focus on the whole crowd, instead of just your friend. So, in order to manifest your creative vision, you’ll have to adjust the f-stop on your camera manually. In manual mode, you’ll be able to selectively focus on the grad.

This guide will give you the know-how to use manual mode to artistically interpret a scene in scenarios such as this.

In this guide, we’ll cover:

  • Where F-Stops Make a Difference
  • What Is an F-Stop?
  • The ABCs of Apertures
  • How to Harness the Light That Shines Into Your Camera Lens
  • The F-Stop Scale
  • Depth of Field (How to Go Shallow and Deep)
  • How to Adjust Your Aperture According to Different Lighting Conditions
  • What It Means to Stop Down and Stop Up/Open Up as It Relates to Your Aperture
  • What Is the Exposure Triangle?


“F-stop” and “stop” are often used to mean the same thing. This is the case throughout this article and out in the wider world, so don’t let this word switch trip you up!

Instances Where Stops Are Frequently Used

You’ll want to adjust your f-stop when you’re shooting landscape, portraiture and macro photographs. Below are a few examples of different apertures to illustrate how adjusting the f-stop can change the look of a photo by adding blur to a background and really letting the photographer select the focus of the image. Have a look, then we’ll explain the number scale and how it works.

Here, the photographer snaps a portrait with an aperture value of f/2.8 to highlight the three faces of friends together and give a shallow depth of field:

Photo by Omar Lopez on Unsplash

Below, the photographer has used a larger f-number (f/6.3) for a macro shot:

This next photo’s stop number is larger still at f/8. (We’ll get into the technicalities of this later, but take note of how this image, at this stop, provides a clearer picture than both of the former shots by keeping the whole scene in focus – a wider depth of field).

What’s an F-Stop?

Your camera f-stop controls two things:

  • How much light can enter your lens (the exposure of your image).
  • The depth of field (DOF) in your image.

The smaller your f-stop number is, the bigger the opening of your aperture.

We know this is counterintuitive, so let’s start by illustrating the concept:

To reinforce this idea in your mind, remember, that the f-stop numbering works in the opposite way you’d expect it to: the smaller the f-number, the bigger the aperture opening and the larger the f-number, the smaller the aperture opening.

A stop is a way photographers like to talk about measuring light. Each movement up a stop doubles the amount of light entering the camera, but decreases the numerical value (for example, going from f/8 to f/5.6 is one stop up).

Each movement down a stop halves the amount of light that comes through your lens, but increases the numerical value (for example, going from f/2 to f/2.8 is one stop down). We’ll cover this concept in greater detail later.

These numbers might seem strange until you understand what exactly they mean. Without getting too much into the complicated math behind f-stops, here’s an easy explanation that may help you get a grasp on why f-stops are written as they are:

F-stops are actually ratios. Specifically, they are derived from your lens’ focal length divided by the diameter of your aperture. They represent a fraction of your lens aperture opening. For instance, an f-stop of f/4 means 1/4th or 25 percent of the lens is open. On a 100mm lens, f/4 would measure 25mm or about an inch.

This fraction is why a lower number is actually a bigger aperture than a higher number. Think of it like a pie – 1/4th of a pie is obviously much larger than 1/8th of a pie (or f/8). A larger opening of f/4 lets more light into your lens than a smaller opening of f/8.

Still, you’re probably wondering why f-stops aren’t all whole numbers. Your f-stop scale includes more numbers than just those halving and doubling exposure. For instance, between f/2 and f/4 you also see f/3.2 and f/3.5. These are thirds of a stop, and they’re there to give you more control.

Luckily, you don’t have to completely understand the math behind f-numbers, but it’s definitely helpful to wrap your head around the basic concept.

We realize it must be tempting to grab your camera and start shooting at this point to test the different apertures, but be patient! If you take your time here to reinforce this concept, you won’t have to revisit this section in the middle of a shoot to double-check your understanding of this tricky idea.

Give it a try yourself by filling in the blanks here – and remember, the answer is the opposite of what you might expect! (Scroll down to the bottom of the article for the answers.)

  1. An f-number of f/1.4 lets in _______ light than an f/4.
    Fill in the blank with either: more or less
  2. _____ lets in way more light than ______.
    Fill in the blanks with either: f/2.8 or f/16
  3. _____ lets in way less light than ______.
    Fill in the blanks with either: f/2 or f/10

Aperture Basics

As we mentioned previously, the aperture is the hole that allows light to shine into your lens (and the f-number measures the diameter of that hole).

To illustrate the concept of aperture, let’s look at how the eye works. Think about how your pupils expand to let more light in when you’re in the dark. This is exactly how aperture works. A larger aperture (lower stop number) allows more light into your camera lens:

A smaller aperture allows less light into your lens (higher stop number):

Photo by ShareGrid on Unsplash

Using a larger and smaller aperture can change the lighting in your photos. A smaller aperture lets less light into the camera’s sensor, forcing the light into a narrow beam to produce more focus and a deeper DOF. Conversely, a larger aperture lets more light into the camera’s sensor to produce less focus and a shallow DOF (scroll down to our ‘Depth of Field’ sections for more on this).


In some lenses, maximum aperture is fixed, but there are lenses on the market (called variable aperture lenses), on which your maximum aperture can change. In variable aperture lenses, your maximum aperture depends on how far you zoom in.

How to Control the Light Coming Into Your Camera

Now that we’ve burdened your brain with so much aperture and stop theory, let’s chat about something practical: how to work those camera controls. Keep in mind, however, that the following may or may not work on your camera model, so you may want to grab your camera manual to see how your specific model works.

  1. First, turn the dial at the top of your camera to ‘Manual’ (M) or ‘Aperture Priority’ (Av – which stands for Aperture Value), or ‘Program Mode’ (P).
  2. Then, press and hold the Av button down (often to the right of your display screen on the back of your camera).
  3. While you’re holding down the Av button, use the dial to adjust your stop up and down.

Knowing about stops is also helpful here:

As we mentioned previously, each movement down a stop reduces the amount of light that comes through your lens by half. Conversely, each stop up doubles the amount of light entering your camera lens.

If you need to double the amount of light, stop up; if you need to halve it, stop down. Here, we’re talking about your f-stop, but you can stop up or down by using your ISO or shutter speed as well.

The F-Stop Scale

Now, it’s time to grab your camera for some hands-on experience. Quickly find a scene you’d like to capture (it doesn’t have to be fancy; anything that’s at your fingertips will do at this point). Then, snap several photos, and change your f-stop each time. Next, have a look at the resulting photos – notice how the levels of crispness and light change in each image.

By completing this exercise, you’ve taken photos along the f-stop scale.

Perhaps they fell somewhere along the lines of a standard f-stop scale, which looks like this:


Your camera will come equipped with a certain range of apertures. The typical aperture range on a camera is f/1.4, f/1.8, f/2, f/2.8, f/3.5, f/4, f/5.6, f/8.

Take note that you may also be able to find aperture maximums or aperture ranges on your lens barrel.

Depth of Field

Simply put, depth of field (DOF) is how much of your image is in focus compared to how much of your image is out of focus (or blurry).

Shallow DOF

Shooting with a shallow DOF simply means that less of your image is in focus.

Lenses with a wide aperture (and smaller f-stop number) are best for shallow depth of field.

If you’d like a couple of f-value starting points, f/1.2 or f/1.4 are ideal for creating a very shallow DOF.

Deep DOF

Shooting a deep depth of field means most – or everything – in your image is in focus. The sharpness and clarity in this photo of roaming elephants exemplify a deep DOF:

To keep both the foreground and the background in focus, try using stop settings of f/16 or f/22 (in fact, anything over f/11 should do). Also, when you’re in the deep DOF range, use the Sunny 16 Rule: On a sunny day, it’s best to use stops of f/16 or higher.


If you love shooting with a deep DOF, you are not alone. During the Great Depression, there was a group of photographers who called themselves Group f/64. Famous photographers, including Ansel Adams and Imogen Cunningham, were members. The group’s mission was to make sure they captured their subjects realistically. So, they were committed to deep DOF to reveal sharp (and therefore, more realistic) images.

They were against the Pictorialist movement of their time because Pictorialists favored images with softly focused subjects and preferred images that resembled drawings or paintings. The photographers in Group f/64 were set on creating art with their photos. Follow in their footsteps by committing to a particular style, and making a series of photographs that adhere to that style. This may put you even more in touch with your artistic style.

Focal Length (and How This Impacts DOF)

While we’re on the topic of depth of field, let’s talk about another setting you can control as a photographer that will impact your DOF: Lens focal length.

The lens focal length controls your field of view (or FOV), which refers to what you see in your viewfinder:

  • The larger your focal length, the smaller your FOV (good for isolating a particular subject, like a person in a field)
  • The shorter your focal length, the larger your FOV (good for capturing a wider, landscape-type nature scene)

“OK, great,” you might say. “But how does this affect depth of field?”

The shorter the lens focal length, the deeper the DOF. The opposite holds true: The longer the lens focal length, the shallower the DOF.

We realize this adds another element into the mix, but, once you’re feeling confident with adjusting stops to control DOF, you can start adding lens focal length to your DOF toolbox.

A few tips to get you started:

  • To change the focal length of your lens, turn the focus ring on your lens to zoom in or out.
  • To see how many millimeters you’ve zoomed in to, look at the scale located at the end of the lens (the end that attaches to the camera).
  • If you snapped a great shot where you loved the focal length you used, you can go back into the properties of the photo to see where your focal length was so you can replicate the same focal length later.


Lens focal length is more than a setting on your camera. You can change up your lens to change your focal length as well. Purchase a lens with a longer focal length if you’d like more shallow DOF shots and a wide-angle lens for deeper DOF images.

How to Adjust Aperture According to Different Lighting Conditions

When you’re a beginner, we recommend shooting in aperture priority mode (find out more about this mode below).

In general, if you are in darker surroundings, you need to open up your lens to a wider stop. Try starting at a setting of f/5.6.

Conversely, lighter conditions will require you to close your aperture to a smaller stop. To start, f/16 is good setting for bright light.

What It Means to Stop Down and Stop Up/Open Up Aperture

Let’s open this section slightly differently: with a pop-quiz! Here’s a chance to intuit the answer from what you’ve learned so far.

If someone asks you to “stop down,” you:

a. Increase your stop number
b. Decrease your stop number
c. If you’re photographing your subject on a staircase, tell them to go down a step.
d. Realize that it’s time for another tricky photography vocabulary learning moment.

If you chose a., you’re technically right, but if you chose d., we’ll still give you the point.

So, if someone asks you to “stop down,” you’ll increase your f-number.

On the other hand, if someone were to ask you to “stop up” or “open up your aperture,” you would decrease your f-number. Think of stopping up as going up in size.

Honestly, you don’t really need to learn anything extra from the theory you’ve already learned from this guide. The only thing you need to know is that, in “stopping down,” the word “down” refers to what’s happening to the aperture.

See what we mean by reviewing the following chart:

What’s the Exposure Triangle?

For proper exposure, you need three elements working in tandem: shutter speed, ISO and aperture. These elements all control the amount of light entering your camera, but they each do so in their own unique way.

We’ve already talked about what aperture is (the hole that allows light into the lens of your camera). However, let’s briefly review ISO and shutter speed.

Your ISO is the sensitivity of the digital sensor in your camera. When the ISO value is higher, your camera doesn’t need to collect as much light for the right exposure.

To learn about ISO using LEGO, check out this PHLEARN video:

Your shutter speed refers to the amount of time light is allowed to hit your camera’s sensor, measured in seconds. A faster speed lets in more light (resulting in a brighter image), and a slower speed allows less light in (resulting in a darker image).

Check back in with Aaron (and LEGO) with another PHLEARN video on shutter speed:

The main similarity between changing your f-stop to adjust aperture and changing your ISO or shutter speed is that all three will impact the exposure of an image. However, to alleviate any possible confusion about the key differences, refer to the following chart:

We’re sorry if we’ve left you scratching your head, wondering how this all fits together. Let’s use a popular analogy on the topic to get us back on track.

Imagine your camera is a window with shutters on the outside. The aperture is the size of the window (the size of the window dictates the amount of light that’s allowed in). The shutter speed is like the shutters on the window (the longer those shutters stay open, the more light is let into the house). To complete the analogy, imagine there’s a person inside the room wearing sunglasses to represent the ISO (the sunglasses make the wearer less sensitive to incoming light).

Tweaking any of these elements is going to impact the exposure of your image. Furthermore, each time you make an adjustment of your ISO, aperture or shutter speed, you are going to not only impact the exposure, but the other elements, too. Said another way: if you change one element of the triangle, you are going to have to change the others as well to keep the same exposure.

There’s another reason you have to be careful. Making changes to these elements may impact areas other than just the exposure:

  • Changing aperture results in a change of DOF.
  • Changing ISO can change the noise/grain in a shot.
  • Shutter speed affects how motion is captured.

As you can see, playing with each of these settings to get the proper exposure is an art form in and of itself. To master the triangle, you are going to have to experiment and practice.

Thankfully, there’s a shortcut (see the section below on Aperture Priority Mode) you can use while you brush up on your triangle techniques.


F-Stop vs T-Stop

By now, you know a lot about the f-stop, but have you heard about t-stop? It would be understandable if you haven’t because it’s often found on cinematographer’s lenses. Essentially, the t-stop, which stands for transmission stop, is more accurate at determining exposure than an f-stop. This is because each t-stop lens is tested by the manufacturer being sold. F-stops can be off by about a third of a stop (at most), which can be fixed in post-production. However, many cinematographers may prefer a t-stop lens to help save money in post-production.

Aperture Priority Mode

Aperture priority is a semi-manual mode – to use it, turn the dial on the top of your camera to ‘A,’ or ‘Av’. This allows you to select the aperture, while your camera’s computer calculates the shutter speed for proper exposure.

Troubleshooting Tips:

  1. Use a tripod in case your camera selects a slower shutter speed to eliminate camera shake and allow for a more stable long exposure.
  2. If you opt to go tripod-less, and the camera selects a shutter speed that’s too slow, you can increase the aperture to compensate. Then, your camera will select a faster speed to correspond with the new aperture you’ve selected.

To Wrap Things up…

We’ve covered a lot of ground in this guide. You should have a good grasp on how f-stops affect your aperture, how to control exposure and depth of field by stopping up/down, and have a solid understanding of the theory behind f-numbers and focal ratios.

If there’s one thing we hope you take away, is that the larger your aperture, the smaller your f-stop number will be. It’s not rocket science, but can take a little getting used to when you want to shoot fast without thinking.

Answers to Exercises:

  1. More
  2. f/2.8 lets in way more light than f/16.
  3. f/10 lets in way less light than f/2.
Seth Kravitz

Seth is the CEO of PHLEARN and an avid writer, photographer, startup investor, and business mentor in Chicago. He joined PHLEARN in 2016 and has been focused on expanding the community to reach millions of new Phans and make learning fun for the next generation of great artists.



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