What is Aperture? Understand Camera Aperture Guide

Photography is one of the most amazing artforms in the world. What could be better than immortalizing a beautiful moment? But rivaling the artfulness is its difficulty- photography can be confusing to get in to, from a slew of settings to learn to figuring out which camera and lens to buy. 

If you’ve ever gone lens shopping, you know that the little numbers are all different- one of which is the confusing F/–.– you will see etched onto the side of a lens! This is called an F/stop, and the F/stop refers to the lens’s aperture. Aperture, my friends, is one of the most important features in the lens. So what exactly is an aperture, and why should you care about it? 

What is Aperture? 

To talk about aperture, we need to quickly chat about a common photography term, “depth of field.” Depth of field refers to how much of an image is in focus. When a depth of field is shallow, that tends to mean that just the subject is in focus and the rest of the image blurs away. When a depth of field is deep, both the subject, the foreground, and the background are in focus. This background blur is called a “bokeh.”

Depth of field is controlled by the aperture.

The aperture is basically the window in the lens that controls how much light does (or doesn’t) hit your sensor. It’s a hole really, but I like to call it a window because it can ‘open and close its curtains’ in order to control the light impact. If you look inside of your lens, you’ll see the aperture as a round circle with blades. These blades either come together tightly to make a small circle or completely retract to show a big opening. 

The pupil in our own eyes is actually just like a lens aperture! Pupils get wide and round when in the dark to let in as much light as possible, and get smaller in bright conditions to minimize how much light comes in. 

Aperture (also denoted as F-Stop or F/insert-number-here) are the numbers on your camera that can range from f/1.2 to f/64. The smaller the number, the wider your aperture. The larger the number, the narrower your aperture (a bit counter intuitive, I know). The wider the aperture, the more light it lets in and the shallower the depth of field. The smaller the aperture, the less light it lets in and the deeper the depth of field.

What aperture you choose plays a lot into your personal style as a photographer. Some photograph with everything in focus, and some like it super soft and out of focus. 

Aperture and Exposure 

Exposure is the amount of light that reaches your camera. Too much light and your image will be too bright. Too little, and it’ll be too dark. Simple, right? To create exposure, you need your ISO level, your shutter speed, and (you guessed it) your aperture. Exposure is a formula.

ISO + shutter speed + aperture = exposure. 

Like a mathematical formula, if one variable is changed, the rest are affected by the change. 

Here is their correlation, broken down in the simplest of explanations: 

The ISO is your camera’s sensitivity to light. The lower the ISO number, the less sensitive the camera is to light (but the less noise the photograph has). The higher the ISO number, the more sensitive the camera is to light (but the more noise the photograph has). Noise are the obnoxious little specks you see in photographs. 

Tip: ISO are the numbers on your camera that range from 100 – 126000 and higher. For most cameras, anything above 2500 ISO starts to show a little bit of noise, and it goes up from there.

The shutter speed is how fast your camera takes the photograph. The higher the shutter speed number, the more frozen the action will be (but the photograph will be darker). The lower the shutter speed number, the more motion blur your photograph will have (but the photograph will be lighter).

Tip: Shutter speed are the numbers on your camera that range anywhere from 1/-15 to 1/8000. 1/2000 – 1/4000 are the best to freeze action. 1/300 is great for portraits. Anything lower than 1/100 will begin to slow the camera down a lot.

Now, the aperture. The lower the aperture number, the more light the camera lets in. The higher the aperture number, the less light the camera lets in.

My tip on how to best work this formula is to eliminate one changeable component. The one that I always keep stable is the aperture. Because the aperture affects your depth of field, I always set my aperture to be as wide or narrow as I want for my photograph. Then, all I have to do is adjust my ISO and shutter speed in order to expose the image properly. Much easier to change two settings than trying to change three settings at once. 

Variable Aperture

Some lenses don’t have apertures that you’re able to control. These apertures change their width depending on how much or how little you change the focal length. The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, and this is denoted in millimeters. 

Some zoom lenses will have their aperture range from wide when the lens is zoomed out to narrow when the lens is zoomed in. This can be problematic if you’re shooting in difficult lighting conditions because you’re not able to control how much light lets into the lens as easily as when you can keep the aperture the same size. However, these lenses tend to be lighter and less expensive, which is a big bonus! 

An example of a lens with a variable aperture is Canon EF 75-300mm F/4-5.6. The aperture starts out at an F/4 when the lens is at 75mm but then gradually changes to an F/5.6 as the lens is zoomed all the way to 300mm. 

Fixed Aperture 

These are the lenses you’re going to want to look at. Fixed apertures are apertures that you can control, and they do not change their width unless you manually make them. These apertures can also be significantly wider than variable apertures, such as widths of F/1.2, F/1.4, and so forth. That being said, because of the consistent aperture, these lenses can be much heavier and are definitely more expensive. 

An example of a lens with a fixed aperture is the Canon 70-200mm F/2.8 L IS USM. The aperture stays a consistent F/2.8 throughout the entire zoom range, from 70mm all the way to 200mm. 

How Do You Control Aperture?

Aperture can be controlled in a variety of ways. You can either let the camera set it automatically with an Auto mode or you can manually toggle the aperture. 

Outside of Automatic, cameras tend to have two other modes: Manual Mode and Aperture Priority (AP) Mode. 

Manual Mode is when you control all of the variables yourself manually (as the name implies). 

Aperture Priority Mode is when you set the aperture you want to keep and the camera adjusts the ISO and shutter speed accordingly to ensure exposure is ideal for your aperture selection.

I don’t personally like Aperture Priority mode because you have to remember that cameras are machines and not brains- they should not think for you. The camera’s programming may suggest that a specific exposure is ideal, but when you look at the photograph, you may not like what you see. In Manual Mode, you are the one who dictates how a picture should be exposed. 

Some lenses have something called an Aperture Ring on them. This looks similar to your focus ring, you just turn it! The Aperture Ring allows you to control the aperture directly on the lens rather than having to go through the camera. This is very common in videography lenses as it’s more difficult to control the aperture in the camera when it is filming something- but this feature has started to spread to more and more lenses as of late. Sony and Sigma both have Aperture Rings on their photography lenses. 

How Does Aperture Factor into the Lens Cost?

A quick Google search on lenses will likely show you that lenses with wider apertures are more expensive than lenses with shallow apertures. Lenses with fixed apertures are more expensive than lenses with variable apertures.

The reason lenses with small aperture numbers are so expensive are because the low number allows you to photograph in low light with higher quality. They’re also more complex to make. This is because a wide aperture lets you use a low ISO number and a high shutter speed number without getting a lot of noise. 

My rule of thumb was always to invest in lenses with a lower aperture number, because you can always narrow the aperture (increase the number) but you cannot decrease lower than its maximum! Remember, it is always easier to raise your aperture up if the image is too fuzzy for you, than to have a lens that doesn’t go any lower. 

Deep Depth of Field 

Deep depth of field is when more of your frame is in focus. For example, the background, subject, and foreground are equally in focus and clear. Deep depths of field are from narrow apertures. 

Although a blurry background has become the trendy type of photograph, deep depths of field are found often with landscape photographers, astrophotographers, and photojournalists. When the location is as much a part of the story as your subject, a deep depth of field is really key! 

Since aperture doesn’t jump from either shallow and blurry or deep and in-focus, you will often be ranging in your depth of field depending on your photography. For example, many headshot photographers use a deeper depth of field because they want the subject’s entire face in focus but not so deep that the background is in focus too. The sweet spot is around F/8.0!

Just remember that the narrower you make your aperture in order to create a deeper depth of field, the darker your photograph will be. Deep depths of field work best in bright and sunny conditions, and can be very difficult to achieve in lower light. 

Shallow Depth of Field

Shallow depth of field is the quintessential ‘professional photograph’ look. A lot of this is due to the average person not being able to take a photograph with this particular look! 

Shallow depth of field is when the subject is in focus and the rest blurs away. This allows a beautiful separation between the subject and the background and ensures that attention is not taken away from the main point of the photograph. 

Shallow depths of field are great to use when the background is less than ideal and distracts from your subject. It’s also great for detail shots so that your audience focuses only on the parts you want them to see. 

Shallow depth of field is great for low light because the wide aperture makes the most use of the available light! However, you will need a filter for bright locations. 

The Big Problem: Focusing with Wide Apertures 

As great as shallow depths of field sound, to any new photographer who has tried it, you may find that focusing is more difficult when you’re playing with wide aperture numbers of F/2.8 and lower. The most difficult is F/1.2 (the widest on most lenses. There are some specialty lenses that go to F/0.95, but they’re very niche and hard to find). 

When you focus your camera on a subject, it establishes a focal plane. To get your subject in focus, it has to be on the focal plane. Focal planes are imaginary horizontal or vertical lines. Anything that stands on the imaginary line will be in focus, and anything not on the line will be out of focus. Simple, right? 

Well, the problem with a wide open aperture is that your invisible line is very narrow. As you decrease your aperture number and make the opening wider, the invisible area in front and behind the plane of focus will get smaller and smaller. When shooting super wide open, like F/1.2, even the smallest movement out of the invisible line will cause your subject to be out-of-focus.

Fear not, there is a simple solution to this dilemma: just move further away from your subject! 

The farther away you are from the subject, the easier it is to get the subject in focus. You can get the subject in focus and still maintain an extremely creamy depth of field. This is because as you move back, your subject becomes smaller, and as such, fits on your invisible line better. This is how you can keep a creamy soft depth of field and still have your whole subject in focus. With new technology and higher megapixel counts, cropping a bit tighter in is a breeze!

What Aperture Should You Use? 

What aperture you should choose depends on a number of factors. Ask yourself these three questions first:

How much does my subject need to be in focus? 

What is the lighting like at my photo shoot location? 

What is the aesthetic for this photo shoot? 

The first question already creates your baseline. If you’re shooting products or fashion, more of your subject needs to be in focus to show off the item you’re capturing. But if you’re photographing dreamy portraits, then you will want a more shallow depth of field. 

Since the aperture is the direct pinhole that lets light hit the camera sensor, you also have to factor in what the lighting is like at your location. If your location is super sunny and bright, but you need to use a shallow depth of field, throw on a neutral density filter (this limits the amount of light that hits your sensor)! But if you do not have a neutral density filter, you’ll need to go with a narrower aperture. Likewise, if your location is very low light, you’ll need to use a wider aperture to work with the available light or bring in artificial lights to shoot a deeper depth of field. 

Depth of field correlates directly with aesthetic- deeper depths of field look more editorial or photo journalistic, while shallower looks appear more whimsical or portrait-like. The type of photographer you are relates heavily to this choice. 

Bonus: Why is Aperture Also Called F-Stop? 

The reason apertures are denoted by F/–.– is because this is actually a mathematical formula where F is the focal length, the slash mark indicates division, and the number given denotes the radius of the aperture opening.


Now that you know what aperture is, it will become easier to make a lens choice! 

Remember, you can always narrow an aperture but you cannot make it wider than its widest point- so look for lenses with wider apertures so that you have more versatility. Fixed apertures can be controlled, variable ones cannot. 

The aperture plays directly into the exposure equation, so try to decide your aperture prior to adjusting the ISO and shutter speed (as this will make your settings easier!). 

Finally, play around with shallow and deep depths of field and figure out where your personal style lies. Now go out there and capture great photographs! 

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