Sunday, September 8, 2013

Zooming vs. Cropping: perspective in photography

One of the most basic decisions when taking a photograph is what to include within the frame, and countless books, articles, and blog posts have been written about composition within that frame. But one often overlooked aspect of this discussion is the difference between zooming and cropping when getting to the final composition.

A wide shot in the process of being cropped down to a closer-in shot.

Zooming, of course, is changing the length of your lens to create the final composition (whether on a point-and-shoot, DSLR, or any camera in-between). Zooming happens in the field, while you are taking a photograph. Cropping, on the other hand, is changing the photograph itself, after it has been taken, by selecting a smaller section of the original photograph to make the final image. Zooming happens with your lens or with your feet; cropping happens on your computer.

The distinction matters for several reasons. One is that cropping decreases the amount of pixels in your final image, which can impact how well you can blow up and display or print the final image. The second is that how you choose your zoom (based on where you stand) impacts the perspective of the final photograph, while cropping does not. Wide angle lenses (or wide focal lengths) tend to expand and distort perspective, while zoom lenses (and narrower focal lengths) tend to compress a scene and make objects seem relatively closer together. These different focal lengths can greatly change the perspective of your scene.

Why does changing perspective matter? Let me illustrate with an example.

I recently retired my car. After fifteen years and nearly 150,000 miles, it was time to start seriously considering a different car before the next winter set in. Decisions were made, and the weekend came to say goodbye to my old car. As a goodbye, I decided to take it for a last spin and photo shoot down by the lake.

I wanted to take a 'car portrait' with the lake and trees as the backdrop, so I decided to take a series of shots at different zoom lengths to see which one offered the best perspective. To accomplish this, I had to zoom with my lens as well as my feet. For the first image, at 18 mm (the widest focal length for the lens I was using), I was standing very close to the car, slightly in the road itself. For the 35 mm shot, I had to back up to just across the road. This gave me the same compositional placement as the first shot (with the car the same approximate size within the frame). Then I repeated the process of backing up and taking another picture at 50, 100, 150, 200, and 270 mm (the maximum zoom amount for the lens I was using).

Zooming Vs. Cropping: perspective in photography | Boost Your Photography
Impact of changing focal length (and backing up) on perspective.

This collage shows six of those images, each shot at the same ISO (100) and aperture (f/16). The top row of shots was shot at a shutter speed of 1/100th of a second, and the bottom row of shots was shot at 1/60th of a second (to make the darker tree backdrop a little lighter). The differences between each of the shots are purely a result of the changing perspective from each of the different focal lengths.

Comparison of 18 mm and 35 mm focal lengths on perspective

The differences are quite apparent when comparing the widest shot, 18 mm, with the next widest shot, 35 mm. The 35 mm length is considered to be most similar to the view and perspective that is captured by our eyes, and this photograph matches how the car 'naturally' looked to me at the time. The wider 18 mm view creates distortion in closer objects, which exaggerates the lines of the front of the car in particular. This view of cars is often used to make them seem large, grand, or imposing, as the car seems to dominate over the wide views in the background.

This distortion of objects at wide focal lengths can create problems when photographing portraits. While a distorted look is common in photographs of cars, a wide angle and up-close photograph of a person is far less flattering and tends to over-emphasize features, making noses look large or faces look wide. This is why lens in the 85-120 mm lengths are often referred to as 'portrait' lenses: these focal lengths give a perspective of the human face that is considered more flattering.

But back to the discussion of cropping. While I can crop an image I took from farther away to make it look like I was standing closer to that object or using a longer zoom, cropping cannot replicate the changes in perspective from actually standing closer to that object.

Same image file, as originally shot (left) and cropped down (right)

The photograph on the left was taken with the 18 mm focal length while I was standing at the same location as the 270 mm version with the car in the same relative position in the frame as in the series above. The photograph on the right was cropped from the photograph on the left to create the same relative position and size of the car in the frame.

Comparison of 270 mm shot (left) and 18 mm shot from same location, cropped (right)

This image compares the zoomed in shot at 270 mm (on the left) with the shot cropped in version from the 18 mm to imitate the composition of the 270 mm shot (on the right). The loss of pixels and therefore clarity and detail is evident between the two. The 270 mm shot is 4752 x 3168 pixels, while the cropped version is only 357 x 238 pixels. You should also notice that the perspective between the two shots is unchanged. Cropping in a shot does not change the perspective of the shot. Only zooming in or out for the shot and moving your feet changes the perspective.

Comparison of 35 mm and 270 mm focal lengths on perspective

Standing in one location (such as where I took the 270 mm shot) and changing the zoom on your lens will make photographs that are different. It will not, however, make photographs that have any differences in perspective. The relative locations and impact of the foreground and the background will remain the same. If you want to change the perspective, if you want to emphasize one object over another or influence their relationships to each other, you will need to change your zoom and move your feet.

Moving your feet can impact your photography in many ways. Read up on aperture and how moving your feet can improve your shots here: Remember the Background and Move your Feet.
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