How To: Zoom with Your Feet & Understand Focal Length

You’ve heard the term ‘zooming with your feet’, I’m sure - probably on a forum where you’ve asked for advice on a zoom lens and someone has come back with this smart retort. Truth is, while this is one way of dealing with perspective, as in all aspects of photography there is no right or wrong answer: it’s more to do with informing yourself with the facts and making a decision based on your own needs.

So, what do people mean when they say ‘zoom with your feet’? Well, generally it means using a prime lens and physically moving forwards or backward to frame your shot until you’re satisfied with your perspective, as opposed to standing in the same place and using a zoom to adjust your composition.

Whilst in theory this works in terms of ‘how’ you want to frame your subject within your composition, the ‘how’ is also the very thing that changes depending on what lens you have attached to your camera. Traditionally speaking, wider lenses ‘distort’ and longer lenses ‘compress’ - so effectively what this means is that as you increase the focal length of your lens, your subject in focus will appear closer to its background/foreground the longer your lenses get.

You’ll notice from the image of our lovely office dog Patrick that even though both images are framed in a similar way proportionally, with the 14mm lens I was within 1-2 feet of his face, whereas with the 135mm, I was probably a good 9-10 feet back.

As you can see, even though the dog is positioned in the same place, the nearest object behind him appears much farther away on the 14mm lens than on the 135mm.

To illustrate this further, we took some portraits of our assistant Zak at different focal lengths just to show how distortion diminishes as you increase focal length.

At 14mm, framed at a distance where you might traditionally shoot a head and shoulders portrait, distortion gives the effect of ‘camel-face’, as Zak quite wittingly pointed out.

At 20mm, distortion is still evident, whilst the objects behind Zak appear to have got closer to him.

At 24mm, the face is beginning to normalize somewhat but still exhibits distortion when compared to what the eye sees.

A 28mm lens is probably the last (common) focal length that can be considered a proper wide shot - whereas a 35mm is regarded as a wide to normal. Although some distortion is present, the face is beginning to look more ‘normal’ and, in the absence of a side-by-side comparison with a 50mm and above, you probably think this is an accurate likeness.

A touch of distortion here, but only comparatively to looking at Zak with my own eyes. At this focal length, the eye understands the image it is seeing as normal relative to its distance from the subject.

The classic 50mm look and almost no distortion to speak of, at least not from a layman’s point of view. If this portrait was sold to you as normal, you’d likely accept it as a very good likeness to reality. Although extreme compression has not set in, the difference in the background relative to Zak’s position is quite telling of the difference in optical characteristics going from a super-wide lens to a standard lens.

An 85mm is enough to have most photographers dribbling, especially a fast 85 - allowing for super-shallow depth of field. Some argue that whilst the 85mm might not be as realistic as a 50mm, it is the most flattering and you’d struggle to disagree. Comparing this to the 50mm, you can see how the background has crept in behind Zak - we are now firmly in telephoto land.

Another favourite for portrait shooters is the 105mm - a lens popularized by Nikon’s legendary f/2 DC and more recently revived by Sigma with their f/1.4 version. As you can see, Zak’s face is rounder and a far cry from the wider lens perspective.

Finally, we have the 200mm with its power to render the background beautifully out of focus. Whilst the 200mm is not as natural as 50mm or 85mm in rendering a portrait, you’d struggle to spot this unless you had a side-by-side comparison.

Ultimately, this is a question of choice - ‘normal’ is normal in terms of what your eye sees. The reality is that all these lenses are ‘normal’ since they each exhibit characteristics in rendering a scene that is unique to their focal length. It’s worth noting that the wider lenses distort in this way simply due to proximity - traditionally, these lenses are not designed with portraiture in mind, but to capture a wide scene where the subjects might be quite some distance away. Whilst there would still be some distortion present, it would be much less pronounced.

So next time someone scoffs at your ‘need’ for a lens and suggests you ‘zoom with your feet’, remember that whilst it’s usually possible, it’s not always a good idea. Thinking of upgrading? Don't wait to sell or trade your used kit.