There’s a common maxim touted in photographic circles, especially in online forums and message boards. It states that some of the limitations of shooting with a prime lens can be overcome by simply moving your body around. The idea of “zoom with your feet” or SneakerZoom, as it’s sometimes called, is often used as a panacea for those who think prime lenses are limiting in terms of what they can do compared to their zooming counterparts.
To a certain extent this is true. If you want to get closer to your subject you can just physically move your body if you don’t have a zoom lens, but doing so results in images that are not at all the same as using a zoom lens. Zooming with your feet is somewhat of a misnomer because zooming implies a change of focal length. But when you move around with a prime lens you are not changing the focal length at all. Instead, you are recomposing with your feet. In this article I’ll explore why this is a simple but significant difference using a few examples below.
How lenses work
To understand how lenses work it’s important to know a few things. The focal length is a measurement of the distance between the optical center of the lens (the point at which incoming light converges) and the image sensor of the camera to which it is attached.
Many cameras come with what’s known as a kit lens. Most of those cover a relatively modest range of focal lengths, with the most common being about 18mm to roughly 55mm. At 18mm, the lens bends light in such a way that the incoming light converges on a point 18mm in front of the image sensor. This results in a field of view that is about 76 degrees wide. (Assuming you are shooting with a crop-sensor camera like a Canon Rebel or Nikon D3300. On a full-frame camera like a Canon 5D Mark IV or Nikon D810 it would be about 90 degrees.)
At 50mm, the angle of view changes to roughly 31 degrees. The practical implications for this are that you can simply fit more in the frame when shooting at a wider focal length versus a longer one. Take the example of photographing a tree, as you can see in the following illustration.
Angle of view versus moving your feet
Shooting at 18mm would allow the photographer in this example to fit the whole tree in the frame, but unfortunately this photographer is using a 50mm prime lens that does not zoom in and out. At this point, you might be thinking, “No problem, just walk backwards to get the whole tree in the frame”. My good friend Bob Slydell from the movie Office Space would respond, “Just a second there, professor.” While it’s true the photographer could walk backwards and reposition himself such that he could fit the entire tree in the picture, there are two problems with this solution:
- There is a pond filled with crocodiles right behind him
- He would still have a 31 degree viewing angle
No matter how far backward, forward, or sideways the photographer in this example repositions himself, the angle of view with the 50mm lens will still be the same. Theoretically, he could construct a raft and float across the pond in order to fit the entire tree in the frame. But doing so would result in a dramatically different picture than if he just uses a wider lens to begin with. Zooming with his feet, or in this case with a boat, will work to get a picture of the tree, but doing so will alter the other compositional elements of the photo.
An example
To see how this works, here’s a revised version of the image above wherein the photographer has retreated far enough to get the entire tree in the frame. In this example, there are five pinwheels behind the tree that are well contained in the wide-angle shot. While moving backward has solved the issue of getting the tree in the frame, the narrow viewing angle means that not all the pinwheels fit in the shot.
The only way to solve this problem using a Zoom With Your Feet solution would be for the photographer to move way back such that the tree and all the pinwheels could fit in the frame. At which point the original subject (the tree) would be so diminished that the image wouldn’t be the same at all.
Real life examples
Of course, this is a theoretical example, but watch what happens when the same type of scenario is replicated in the real world. I shot the following three images using my 70-200mm lens. Watch what happens as the focal length, as well as the distance to the subject, changes.
Shot #1 – 70mm, from far away
70mm, f/4, ISO 100
Can you tell what the subject is in this picture? It’s supposed to be the artwork in the middle–a boy fishing with his dog, carved from the trunk of a fallen cypress tree. The angle of view in this picture is about 34 degrees (I shot this on my full-frame Nikon D750), which is enough to capture lots of scenery in the frame. Notice how in addition to the boy and his dog you can also see trees, a building, and even some foreground elements such as a pond and grass.
Shot #2 – 200mm, from far away
200mm, f/4, ISO 100
Standing in the exact same spot as before but zooming into 200mm has had a dramatic impact on the picture. Now the viewer’s attention is focused squarely on the carving, and the field of view is now limited to a much narrower 12 degrees. Note where the head of the carving is in relation to the building in this image: it is framed between two columns on the first floor above the ground, which is quite different from the next picture.
Shot #3 – 70mm, shot from close up
70mm, f/4, ISO 100
This final photograph was made by zooming with my feet, I repositioned myself to be much closer to the tree carving. The resulting image is similar, in that the carving itself is roughly the same size as in the 200mm shot, but the field of view is 34 degrees because I shot this at 70mm. Even though the subjects are similar in shot #2 and shot #3, the pictures are entirely different!
The wider field of view in shot #3 resulted in an image with a lot of background elements that distract the viewer. The boy’s head is now positioned near the top of the building, despite the fact that my camera was the same distance above the ground. While the classic SneakerZoom technique has certainly worked to get my subject looking how I wanted, the end result is quite different from actually using a proper zoom lens.
Zooming with your feet is NOT the same
These examples show that while you certainly can zoom with your feet, doing so is not the same at all as zooming with a telephoto lens. When you move around you are not really zooming but recomposing. While this is not a bad thing, it is something to be aware of when choosing lenses or honing your photography technique.
As another example of this phenomenon, here are two pictures from a recent session I did with a local family. I shot the first one with my 70-200mm lens. It’s a traditional portrait-style image with a blurred out background with the focus squarely on the faces and upper bodies of both women.
200mm, f/2.8, ISO 100
I then zoomed all the way out to 70mm in order to get a closer, more personal image of the two women. After changing to a 70mm focal length I had to walk much closer to the ladies, essentially zooming in with my feet, in order to get them to appear the right size in the frame. The resulting image feels entirely different, not just because they are sitting on the ground showing off their matching wrist tattoos, but because you can see that they are sitting in the middle of a green field strewn with autumn leaves.
70mm, f/4, ISO 100
Shooting at 200mm meant a highly compressed field of view with only a small slice of the trees and background visible. Whereas in the bottom picture you can once again see the effects of the wider viewing angle afforded by shooting at 70mm.
Different planes
One final example that’s necessary to illustrate this phenomenon, is when you and your subject are not on the same horizontal plane. In these situations, changing your focal length can bring you much closer to what you are trying to shoot, whereas walking around will significantly alter the scene, based on the foreground and background elements, as well as the angle from which you are viewing the subject.
Shot #1 – 70mm, from far away
70mm, f/4, ISO 100
This image looks decent, but I didn’t like how the flags shared the frame with the building behind them, especially the chimney in the corner with the radio antenna. Since I shot this at 70mm I had a couple options to improve the shot; including zooming into 200mm or zooming with my feet to get closer to the flags. I started with the first option and was very happy with the result.
Shot #2 – 200mm, from far away
200mm, f/4, ISO 100
Zooming with my lens gave me a much better picture. One that focuses entirely on the flag pole with no distracting background elements and a nice cloudy sky to help the flag pop out of the frame. One tradeoff is that the Oklahoma flag is no longer visible. I could have zoomed in only partially to 135mm if I wanted to include it, but I decided that the picture would be more impactful if it just had a single subject instead of two flags. After getting this shot I zoomed in with my feet to see if I could get a decent picture at 70mm by moving much closer to the subject.
Shot #3 – 70mm, shot close up
Look at how different this final image is compared to the 200mm version! While I was able to get the United States flag much larger in the frame, I ended up shooting from such a low angle that the flag pole itself draws almost as much attention as the banners it is holding. The Oklahoma flag is also visible in this version, which has the unfortunate side effect of creating an image that is unfocused and busy. There are now two subjects in the frame (three if you count the pole.) This leaves the viewer with a sense that the image is cluttered and unfocused. Zooming with my feet did allow me to get closer to the subject, but it altered the composition so significantly that the resulting image is unusable.
Conclusion
Hopefully, these examples will help you start to visualize why moving around is not at all the same as changing your focal length. Please understand that I’m not saying you should sell all your prime lenses and rush out to buy a zoom lens, though. I use prime lenses all the time, and by far my most-used lens is the Nikon 35mm f/1.8 for its size, weight, and sheer versatility.
My goal is simply to help you understand that when you are shooting with a prime lens you need to know that moving closer to, or farther away from, your subject does not have the same effect as actually changing the focal length. Once you understand that, you can start using this knowledge to your advantage. You can structure your photo techniques around this important limitation of prime lenses, and hopefully, take much better pictures as a result.
The post Prime Lenses: Can you really zoom with your feet? by Simon Ringsmuth appeared first on Digital Photography School.