Camera Lenses Explained

Whether you’re a photographer, filmmaker or hybrid shooter, understanding how your lens works is every bit as important as honing your camera skills. Here, Canon Collective ambassador Jenn Cooper sheds light on what those numbers on the lens mean, covering everything from focal lengths and aperture values to the different types of lenses and when to use each one.


How Exactly Do Camera Lenses Work?

Lenses work similarly to the human eye and allow you to control the amount of light that enters your camera. Inside each lens is a series of convex and concave optical elements that work together to bend light and refract it into a single sharp focal point.

How Exactly Do Camera Lenses Work


What Does Focal Length Mean and How Does it Work?

Every lens has a specific focal length, or magnification number, which is measured in millimeters (mm). This is normally displayed on the lens itself.

Lens Focal Length

The longer the focal length, the higher the magnification. The shorter the focal length, the lower the magnification. For example, a lens with a focal length of 24mm will offer less magnification than a lens with a focal length of 200mm.


Understanding the Different Types of Lenses and Focal Lengths

Camera lenses come in all shapes and sizes and are designed for different shooting scenarios. Check out the full range of Canon’s lenses here.


Zoom Lenses

Zoom lenses, such as the EF-S 18-55mm f/3.5-5.6 III or EF 24-70mm f/2.8 L IS USM, offer a variety of different focal lengths. This makes them extremely versatile, which is why many photographers consider them to be essential – especially for travelling photographers who don’t want to carry multiple lenses.


Prime Lenses

Lenses that have only one focal length, such as the EF 35mm f/2 IS USM or EF 50mm f/1.8 STM, and are known as prime lenses. Prime lenses don’t allow you to zoom in on your subject. However, because they have fewer lens elements, and fewer moving parts in general, they typically offer superior image quality.

Prime lenses also have low aperture values, such as f/1.8 or even f/1.2, which means they offer a shallow depth of field. This makes them suitable for portraits and product photography, or any type of photography where a soft blurry background is desired. These wide apertures also allow more light into your camera, making them ideal for shooting in low light conditions.


Telephoto Lenses

Lenses with larger focal lengths are called telephoto lenses and offer greater magnification when shooting subjects that are far away. For example the EF 100-400mm f/4.5-5.6 IS II USM lens is often used for wildlife and sports photography, allowing the photographer to zoom in on the animal or athlete when it is not possible to get close to them.


Wide Angle Lenses

Wide angle lenses, such as the EF 10-22mm f/3.5-4.5 USM or EF 16-35mm f/4 L IS USM, have smaller focal lengths and can capture a wider perspective. This makes them suitable for landscape photography, or any type of photography where you are shooting in tight spaces, like architecture/interior photography.


Macro Lenses

Macro lenses allow you to zoom in and focus on subjects at extremely close distances. Macro lenses such as the EF-S 35mm f/1.8 Macro IS STM, enable the objects to look larger than life size with greater detail. This is ideal for magnifying insects, flowers or manmade objects and capturing them in extreme detail.


What is Aperture (F-Number) and How Does It Work?

The aperture of your lens is the opening that allows light to enter and reach your camera’s sensor. It can be adjusted much like the irises of the human eye, which dilate or contract depending on the available light. In photography, the aperture of a lens is measured in F-numbers or F-stops and is typically expressed on your lens like the following: F/4.5-5.5. In this example, the minimum aperture for that lens ranges between f/4.5 and f/5.5, depending on what focal length you’re using. In general, the smaller the F-stop, the larger the aperture opening, and vice versa.


Depth of Field

Aperture also controls depth of field, which is used to separate your subject from the background. A small F-number, such as f/1.8, will give you a sharp focal point with a soft blurry background. A larger F-number like f/16 will give you a larger depth of field, resulting in both the foreground and background being in focus.


Low Light Benefits

Selecting a small aperture like f/2.8 will let more light through the lens, which means you can shoot in low-light with a lower ISO and faster shutter speed. On the other hand, f/16 will limit the amount of light passing through the lens, meaning you will need to compensate by selecting a higher ISO or slower shutter speed to achieve the same exposure. The relationship between these three functions is commonly known as the Exposure Triangle Basics.


What is ISO and How Does it Work?

ISO controls your camera sensor’s sensitivity to light. A lower ISO, such as ISO 100 or 200, is used in bright daylight or when shooting well-lit indoor scenes. Higher ISO levels, such as ISO 3200 or 6400, allow your camera to operate in low light conditions. However, the trade off is that high ISO levels introduce digital noise to your images. Where possible, it’s always best to shoot with a low ISO to maintain the best image quality.


Which Cameras Have Interchangeable Lenses?

Canon’s DSLR (Digital Single-Lens Reflex) and mirrorless cameras are designed to have interchangeable lenses. This allows you to use the same camera body with a variety of different lenses. For example, a DSLR camera gives you the flexibility to use an EF 50mm f/1.4 USM prime lens when shooting portraits or an EF 70-300mm f/4-5.6 IS II USM telephoto lens when shooting wildlife.


Which Lens Can I Use With My Camera?

It’s important to know which lenses can be used with your camera. If the name of your lens starts with EF, EF-S, EF-M or RF, this indicates what type of lens mount your camera has. Each lens mount connects to their respective camera bodies.


EF Lenses

EF lenses are Canon’s professional range of lenses. These are indicated with a red dot and commonly feature a red ring around the outside of the lens which is the signature for our L series lenses. These can be used on all Canon DSLRs, and on Canon’s mirrorless cameras when using an adapter.


EF-S Lenses

The EF-S lens mount is indicated with a white square on the lens and matched with the white square on the camera body. These lenses can be used on Canon DSLRs with APS-C sensors, such as the EOS 200D, EOS 80D and EOS 7D Mark II.


EF-M Lenses

EF-M lenses are designed for Canon’s EOS M mirrorless cameras, such as the EOS M50. These are the smallest of Canon’s interchangeable lens range, making them ideal travel cameras.


RF Lenses

RF lenses feature Canon’s newest lens technology and have been designed specifically for the Canon EOS R and EOS RP full frame mirrorless cameras.

Check out one of Canon Collective’s beginner courses to learn more about the fundamentals of photography.

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