Mastering the F-Stop: A Guide for Photographers Who Don’t Love Math (2024)

A larger aperture lets more light into the camera’s sensor to produce less focus and a shallow depth of field. Conversely, a smaller aperture forces light into a narrow beam that produces more focus and a wider depth of field. (Don’t worry, we’ll get into depth of field a little further down.)

You can probably gather from this that darker scenes will usually require a wider f-stop, while bright scenes require a more narrow f-stop, to avoid overexposure. That’s really the most crucial thing to understand about aperture: how to use it to maintain detail and definition in your highlights and shadows, regardless of the light you’re contending with at any particular moment.

Tip

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.

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). Now snap several photos, changing your f-stop each time. 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.

Depth of Field

Simply put, depth of field 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.

Photo by Kelen Loewen on Unsplash

Lenses with a wide aperture (and smaller f-stop number) like f/1.2 or f/1.4 are best for shallow depth of field.

Deep DOF

Shooting a wide depth of field means most – or all – of your image is in focus.

Tip

If you love shooting with a wide depth of field, 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 wide depths of field 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 portraits that resembled drawings or paintings.

Focal Length (and How It Impacts Depth of Field)

Lens focal length can also affect the depth of field in your images. Your focal length controls your field of view (FOV), which is what you see in your viewfinder:

The longer your focal length, the smaller your field of view (this is good for isolating a particular subject, like a person in a crowded place).
The shorter your focal length, the wider your field of view (good for capturing a wider scenes like landscapes).

“OK, great,” you might say. “But how does this affect depth of field?” Well, a wider field of view tends to also yield a wider depth of field. So in general:

Short Focal Length = Wide Field of View = Wide Depth of Field

Whereas:

Long Focal Length = Small Field of View = Shallow Depth of Field

Sounds pretty simple right? But focal length is all about comparisons. It’s possible to still get similar results (with regard to depth of field) from different focal lengths by adjusting the settings we’ve already covered here. Yes, this does add yet another element into the mix, and you can feel free to ignore it if you’re still getting your sea legs. Once you’re feeling confident with adjusting stops to control depth of field, you can start adding lens focal length to your depth of field toolkit.

A few tips to get you started:

To change the focal length of your lens, turn your lens to zoom in or out.
To see how far you’ve zoomed in, look at the scale. It’s usually located at the end of the lens 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.

What It Means to Stop Up and Stop Down

Pop quiz! 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.

If someone asks you to “stop down,” you’ll increase your f-number. If someone were to ask you to “stop up,” you would decrease your f-number. Think of stopping up in terms of aperture size, not the actual number.

Here’s a handy cheat: when you hear “stop up,” think “open up,” because that’s what you’re doing. Don’t worry visual learners, we’re coming at you with a chart:

What’s the Exposure Triangle?

We mentioned it briefly above, but here’s the full story on 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.

By WClarke [CC BY-SA 4.0 ], from Wikimedia Commons

We’ve already talked about what aperture is (the opening that allows light to travel through your lens and hit your camera sensor). Now, 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 your shutter is open, allowing the light from your lens to hit the sensor. This is measured in seconds, or fractions of them. A faster speed (where the shutter is open for a shorter amount of time) lets in less light. A slower speed (where the shutter is open for a longer time) allows more light in.

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

Let’s go back a ways and elaborate on a loose comparison from earlier to help you visualize what each point of the triangle does: if your eye is the camera, the aperture is your pupil. It expands and contracts to accommodate the amount of light you need in a particular situation. The shutter is your eyelid. When it’s open, light can travel through for your brain to interpret into a scene. When it’s closed, you’re out of luck. The ISO is how much light your eye can stand at a time. You know how some people can look right at bright lights while others squint and tear up? Think of that when you think of ISO.

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. If you change one for artistic purposes, you may need to make adjustments somewhere else to keep the light balanced in your image.

What do we mean by “artistic purposes?” Changing your f-stop for light balancing will also change your depth of field. But for artistic reasons you may want exactly the depth of field you already have. In this case, you will need to change something else to get the right exposure. ISO and shutter speed have their own little quirks as well:

Changing ISO can change the noise level in a shot. The higher your ISO, the more digital noise you will see in the end product. That’s why ISO on its own isn’t always the magic cure for a low-lighting situation.
Shutter speed affects how motion is captured. The longer a shutter is open, the more motion and blur it will capture. That’s why sports photographers use super, super quick shutter speeds that will freeze that Play of the Week into a newsworthy action shot.

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 next section on Aperture Priority Mode) you can use while you brush up on your triangle techniques.

Tip

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 most commonly found on a 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:

Use a tripod in case your camera selects a slower shutter speed. This will eliminate camera shake and allow for a more stable long exposure. A remote shutter release will offset any shake caused by your finger pressing the actual shutter button.
If you opt to go tripod-free, 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 or down, and have a solid understanding of the theory behind f-numbers and focal lengths.

If there’s one thing we hope you take away, is that the wider your aperture, the smaller your f-number will be. It’s not rocket science, but can take a little getting used to when you want to shoot fast without thinking. Start practicing with some stationary subjects or still life setups to give you plenty of time to make adjustments and play around. Your comfort level will grow with every shot, and soon you’ll be ready to move on to your next photography adventure!

Answers to Exercises:

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f/2.8 lets in way more light than f/16.
f/10 lets in way less light than f/2.