A Guide to Understanding Focal Length: Camera Zoom & Lenses

A Guide to Understanding Focal Length: Camera Zoom & Lenses

There are many factors that work together to create an image and one of the most important is the focal length of your lens. Photography newbies often think of focal length as being how “zoomed in” to an image you are. While this is true, there is more to choosing your focal length.

Not only do different focal lengths have different fields of view, but they can also introduce perspective distortion and affect the depth of field. Some shots will require a relatively specific focal length, while others may be able to choose between different focal lengths for creative purposes.

Camera lenses have many characteristics. If you’re wondering why should you choose one focal length over another, we break down everything you need to know.

What is Focal Length?

Focal length is the distance from the front of the lens to the sensor. When a lens focuses light onto a sensor, the light is bent in such a way that it converges on itself before continuing onto the sensor.

More accurately, focal length is the distance from this convergence point to the sensor. There is a correlation between the length of the lens and the focal length, but different lens designs can bend the light in different ways. This is why there are “pancake” 50mm lenses that are far smaller than standard 50mm lenses and why some zoom lenses are built with fixed, non-moving front elements. While it might be interesting to know exactly what a focal length is, what is more important is what affects different focal lengths have on an image. There are a few key things to consider.

Field of View/Angle of View

Diagram of Sensors and Angle of View

The field or angle of view is what determines how “zoomed in” a lens is. The shorter the focal length, the wider the angle of view, the more of a scene you are going to capture. Conversely, the longer the focal length, the narrower the angle of view, the more “zoomed in” on an image you will be. This has an obvious impact on the composition of your image, but there might be some flexibility in terms of what focal length you can choose to use. In many cases, if you want something larger or smaller in your image, you can move closer or farther away.

One thing to keep in mind is that by definition focal lengths are the same on all cameras. The distance from the convergence point to the sensor will be the same regardless of what camera you use. However, depending on the sensor size of your camera, the field of view will be different. Focal lengths are generally categorized based on full frame sensors (and 35mm film before that). Because a crop sensor is smaller, it will only record a portion of what a full frame sensor would record, resulting in a narrower angle of view. If you shoot a crop sensor camera, keep this crop factor in mind when choosing a focal length to use. You will need a wider lens to achieve the same image.

Distortion

Motorcyclist on bike with moon in background example by Nick Wrzesinski for BorrowLenses

Example of how relative background size and lens length relate to one another from How Lens Length Affects Apparent Background Size: An Example Using the Moon. Top image taken at 24mm, bottom image taken at 400mm.

Moving closer or farther will make a subject appear larger or smaller in an image, but it also makes everything else appear larger or smaller as well. However, this difference won’t be the same for everything. The closer an object is to you, the more its size will change. This is called perspective distortion or lens compression. In some cases, perspective distortion can be used creatively. Many moon photographs are taken with very long focal length lenses to make the moon appear much larger compared to other objects in the shot than it would appear in real life.

However, perspective distortion can also be a negative you want to avoid. Close up pictures of faces, for example, can suffer significantly from perspective distortion if shot with a wide angle lens. In order to fill the frame with a face when using a wide angle lens, you have to be so close that the nearest facial features (specifically the nose) appear far larger than features farther away.

Additionally, in certain ultra-wide lenses you run into barrel distortion, which is when the angle of view gets so wide that features appear to bend where they don’t in real life. This is most commonly seen in fish-eye lenses where everything seems to get squeezed into a circle.

Depth of Field

depth-of-field-kellan-reck-borrowlenses

Assuming your focus point and focus distance stay the same, your aperture is going to control whether you have a narrow or a large depth of field. Distance from your subject and lens length will also affect this.

Depth of field is how wide or narrow of an area is in focus. This is most commonly associated with aperture, where a large aperture results in a narrow depth of field (and vice-versa), but focal length is another key factor in determining the depth of field.

At any given aperture, a shorter focal length will result in a wider depth of field while a longer focal length will result in a narrower one. A 200mm lens at f/2.8 will have a far narrower depth of field than a 16mm lens at f/2.8 will. If you are wanting to achieve a specific depth of field, focal length should be a consideration in choosing what lens to use.

How to Find Focal Length

woman-taking-picture-street

Luckily, both lens and camera manufacturers make it very easy to determine what focal length you are using at any time. Focal length is shown in millimeters, so look for a number followed by “mm”. You will find this on both the packaging and somewhere on the barrel of the lens itself. For fixed lenses, there will only be one number while zoom lenses will state the range, as in a 70-200mm lens.

With zoom lenses, the range will also be indicated on some sort of gauge that shows the current focal length. This gauge will have key focal lengths notated and a line that points to the current focal length. In some lenses, the numbers will move while the line is static, while in other lenses it’s the opposite.

In addition to looking at the lens itself while shooting, the focal length is saved in the EXIF data of an image file. If you are looking at an image after shooting it, all you have to do is open up the EXIF data and find the focal length field to see this information. Raw image editors, including both Adobe Lightroom and Adobe Camera Raw, also generally display the focal length along with the shutter speed, aperture, and ISO somewhere fairly prominent when working on a file.

Common Lenses: Focal Lengths and Categories

Common Lens Lengths

Depending on the style of photography you shoot, there is likely to be a specific category of focal lengths you will choose to use. Often, just sticking with any focal length within a category will give you the results you want. Other times you may choose a specific focal length out of familiarity or availability. Either way, you should learn what focal lengths work best for what subjects.

Note that all of the focal lengths listed below are for full frame sensors. For crop sensors, factor in the crop factor to determine what focal length category a given lens is in.

Ultra Wide Angle

While some people just simply consider anything wider than 35mm to be wide angle, many sources further subdivide this category and list anything wider than 24mm as an ultra wide lens. Ultra-wide lenses are commonly used when you want the widest possible angle of view, making it a popular choice for landscape photographers shooting epic scenes. It’s also a great option for shooting in very tight environments where you can’t back up far enough to see everything, such as architectural photography (especially interiors).

One concern with ultra wide angle lenses is that some can introduce significant distortion. However, for some photographers, this “flaw” could turn into a creative opportunity to use the distortion for a specific purpose. When you want to shoot ultrawide, think about whether or not you want distortion.

Wide Angle

Lenses with focal lengths of 35mm or less are considered to be wide angle lenses. They allow the photographer to squeeze more of a scene into the frame, making them popular among any sort of photographer that wants to show the environment they’re shooting in. Wide angle lenses are not only good for shooting landscape and architectural photography (as seen with the ultra wides above), but also for full body portraits where you want to see more than just the model. Additionally, wide angles are great for photojournalism when you need to see what’s going on around the subject.

Normal

Normal lenses are those that most accurately recreate the angle of view that one would have when looking at a scene in real life. Theoretically, this works out to be a lens with a focal length equal to the diagonal length of a sensor, or roughly 43mm for a full frame sensor. Because there will be variations in how the image will be viewed (e.g., screen/print size), standard lenses are generally considered anything between 35mm and 70mm.

Normal lenses are commonly used in street photography and photojournalism because don’t introduce the distortion commonly found in wide angle lenses. They’re also great as general walk around lenses and can serve well when photographing wider portrait if you don’t want to go for a full wide angle lens.

Telephoto

Telephoto lenses have focal lengths longer than 70mm. This makes different lenses suitable for different uses, even while remaining in the same category.

Shorter telephoto lenses, particularly 85mm and 135mm lenses, are very popular as portrait and headshot lenses because they eliminate perspective distortion, can achieve nicely thin depths of field, and allow a comfortable working distance that is neither uncomfortably close nor so far away it’s hard to communicate when filling the frame with the subject’s face. 70-200mm lenses are also popular among some landscape photographers who want more intimate shots that isolate specific subjects or parts of the scene.

Mid-range telephoto lenses, such as those from 200mm to 400mm, are popular among sports and wildlife photographers who can get relatively close to their subjects but must still keep some distance. They allow these photographers to fill their frame with subjects that aren’t close while being about as long as you can get and still be relatively easy to hand hold, at least for short periods.

Super telephotos longer than 400mm are behemoths of lenses that are used when you have to keep a lot of distance from a subject. They are most commonly used when photographing wildlife that requires you to stay away, either because of their fearfulness (such as birds) or their danger (such as large predators). Super telephotos are so large and heavy that they will mostly be used with tripods or monopods to support their weight and eliminate the camera shake that is inherent in such a long lens.

Macro

Macro lenses are not tied to a focal length but are determined by how much magnification they can achieve. In order to be considered macro, a lens has to focus closely enough that it can create a 1:1 reproduction onto the camera sensor. The most common macro focal lengths are around 100mm, but there are both longer and shorter macro lenses available. Because the final magnification is the same, the most important thing to consider in choosing a macro lens’s focal length is the working distance to the subject. Shorter focal length macro lenses will need to be closer to the subject, which might be useful when shooting inanimate objects in a small studio (although they might be so close they interfere with the lighting). Longer focal length macro lenses allow you to be farther from the subject which can be more comfortable when shooting living things and give you more lighting options.

Lenses By Focal Length

For landscapes, tight interiors, and using perspective distortion creatively, an ultra wide angle is recommended. Anything 24mm and wider is typically categorized as “ultra wide”. Examples of our most popular ultra wide lenses:

Nikon 14-24mm f/2.8G AF-S ED Lens
Nikon 10-24mm f/3.5-4.5G AF-S DX ED Lens (for crop frame sensor Nikon DSLRs)
Canon EF 11-24mm f/4L USM Lens
Canon EF-S 10-22mm f/3.5-4.5 Lens (for crop frame sensor Canon DSLRs)
Sony FE 12-24mm f/4 G Lens
Sony 10-18mm f/4 OSS E Mount Lens (for crop frame sensor Sony mirrorless cameras)
Fuji XF 10-24mm f/4 R Lens

For architecture, landscapes, events, full body/group/environmental portraits and fashion, a regular wide angle is suitable. Anything between 24mm-35mm is generally considered “wide”. There are zooms that encompass both “wide” and “ultra wide” lengths and offer the most flexibility. The most popular of these zooms is the 16-35mm:

Nikon 16-35mm f/4G ED AF-S VR Lens
Canon EF 16-35mm f/2.8L III USM Lens
Sony FE 16-35mm f/2.8 GM Lens

Most people when starting out will opt for a “normal view” lens, such as a 50mm. It best approximates how the normal eye sees, which is why it is such a great length to learn with. You can go with a prime lens, which is fixed at one length, or choose a zoom that will run the gamut from wide to normal and into short telephoto. Of these, the most popular and flexible are the 24-70mm lenses. 24-70mms are far and away our most popular lenses for travel and events for their high quality, relative portability, and useful range length:

Nikon 24-70mm f/2.8E AF-S ED VR Lens
Nikon Z 24-70mm f/2.8 S Lens (for Nikon’s new high megapixel Z mount line)
Canon EF 24-70mm f/2.8L USM II Lens
Sony FE 24-70mm f/2.8 GM Lens
Pentax D FA 24-70mm f/2.8 ED SDM WR Lens

Beyond this, you start to get into more specialized and expenses lenses suitable for wildlife and sports. However, our most popular lens of all is the 70-200mm. It’s long but still hand-holdable. This length range is excellent for portraits and sports alike. See all of our 70-200mm lenses here.

Conclusion

As a beginner, it’s easy to just slap on a superzoom lens and choose whatever focal length feels right in the moment. Every focal length is going to affect the final image in specific ways. By learning how to choose a focal length, you can take a more mindful approach to your photography, getting the shot you want.

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