Understanding what focal length is and how it impacts your photos is a critical aspect of becoming a better photographer.
In this quick guide, I offer up a few insights into what focal length is, what different focal lengths are typically used for, and how focal length determines how your images look.
What is Focal Length?
The focal length of the lens is often mistaken as the length of the lens from the front to the back.
Though that's a fairly close determination, the focal length is actually measured from the point of convergence of light in your lens to your camera's sensor.
Easy, right?
In layman's terms, a lens's focal length is how zoomed in the lens is.
In other words, the longer the focal length (i.e., a 400mm lens), the more zoomed in the image will be, as shown in the first image above.
Conversely, the shorter the focal length (i.e., a 24mm lens), the less zoomed in the image will be, as shown in the second image above.
Learn more about focal length in the video above by Michromatic.
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Focal Length Determines What a Lens is Best-Suited to Do
Naturally, if you want to take a portrait of your kid and he's 12 feet away from you, you don't need a 400mm telephoto lens to do so.
On the flip side, if you're photographing a street scene, a 10mm super-wide-angle lens is probably not the best bet because it will distort the scene and make buildings look like a reflection in a funhouse mirror.
That begs the question, what focal lengths are best-suited for what tasks?
First Things First - Crop Factor
If you go to a camera shop and see a 50mm lens sitting on the shelf, it's important to understand that that lens will only be a 50mm lens if it's used with a full frame camera.
Full frame cameras have a crop factor of 1:1, so whatever the focal length is that's listed on the lens, that's its effective focal length on a full frame camera.
However, many photographers (especially amateurs) use a crop sensor camera.
Depending on the manufacturer, a crop sensor camera might have a crop factor of 1.5x, 1.6x, or maybe even 2x.
That means you have to determine the effective focal length of a lens.
So, that same 50mm lens on a crop sensor camera with a crop factor of 1.6x would be 80mm.
Just keep that in mind as I discuss the different focal lengths below. The focal lengths I list are for full frame cameras.
For a more detailed discussion of crop factor, check out the video above by B&H Photo Video.
Wide-Angle Lenses
Far and away, wide-angle lenses are most commonly used for landscape photography.
Wide-angle lenses are considered to be anything below 35mm on a full frame camera.
As their name indicate, these lenses offer a wide-angle of view that's ideal for capturing the expanse of a landscape scene, as shown above.
Normal Lenses
Normal or standard lenses are named such because many of them reproduce the scene you're photographing in a way that's close to what our eyes experience.
That's especially true of lenses in the 35-50mm range on a full frame camera (though the range of normal lenses extends to about 70mm).
Normal lenses are highly versatile, and can be used for just about any photographic purpose.
That includes landscapes, street photography, portraits, and even macro photography.
Telephoto Lenses
The longest of the bunch, telephoto lenses have a focal length of about 70mm and up.
Short telephoto lenses (70-105mm) are ideal for close-ups of subjects that aren't that far away, like a portrait of a person or a wildlife shot of a nearby bird, squirrel or another animal.
Long telephoto lenses (105mm and up) are better suited for taking photos of distant subjects.
If you attend a sporting event, the long lenses you see photographers use are telephotos. Likewise, when you see wildlife photographers with enormous lenses, they're using telephotos.
That's because these lenses zoom in quite far, making distant subjects look much closer.
Learn More:
Final Thoughts
Understanding focal length can be a little confusing at first, but with this guide, you should be able to clarify what focal length is and how it impacts the way images look.
Remember, a short lens offers a wide view, a long lens offers a narrow zoomed in view, and lenses in between offer a normal or standard view of the subject.
You can see the difference between the way in which a wide-angle lens and a telephoto lens render subjects in the video above by Adorama TV.
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