Monday, May 28, 2012

Lens "compression?"

Or, why should you get up and move around when making a photograph.

Just a quick question... Which compresses a scene more, a short or a long lens? Don't be so quick to come up with your answer. In each pair of photographs below one was taken with a wide angle lens and the other with a telephoto. Big thanks to one of my favorite models* for obliging me here.

24mm lens at 48 inches
85 mm lens at 48 inches
35mm lens
200 mm lens

While the lens was changed between each image, the camera and subject were stationary. If the camera to subject distance stays the same, the perspective (relationship between objects in the scene) stays the same. The wide angle lens lets you get more of the scene into the frame. The telephoto lens lets you fill the frame more selectively. But for the part of the scene that is common to both the perspective will be the same.

Here's what the original full frame images look like from the short lenses. The images taken with the longer lenses were not cropped.

24mm at 48 inches, no crop
35mm, no crop. Same distance as with the 200mm
However, if you do move the camera, things change dramatically, as seen in each of these non cropped images. By moving in close to fill the frame with the 24mm lens we get a much different drawing of the face than we do filling the frame with the 85mm lens. It isn't the lens, however, that is causing the different looks--it is the camera to subject distance. The lens just lets us fill the frame the with the subject's head at the different distances.

24mm at 12 inches
85mm at 48 inches
Getting physically closer to the subject slims the subject's face by making the relationship between nose to eyes to ears stretch out. As you take your camera and move back away from your subject the nose/eyes/ears are all relatively closer to each other, resulting in a flatter overall look which makes the subject look wider.

This works outside as well as in the studio.

35mm cropped from the image below
35mm full frame
Compare the 35mm** crop here with the 35mm crop in the third image from the top of this post to compare the compression. Same lens, but different camera to subject distances.

Keep in mind that objects close to the camera will appear larger in your photographs. But it is all relative. At 48 inches away your subject's nose, eyes, and ears are all relatively the same distance from your camera. When you move in so the nose is only 12 inches from the camera it is relatively a lot closer to the camera than the eyes and ears, so the eyes and ears are proportionally further away and look much smaller.

Consider this illustration (not to scale)...

In reality (above)

What it appears like from being in close

Pay attention to the relationship between the yellow and green shaded areas above. Note that close or far, the green shaded area remains the same size. In this illustration I have shown the green area as nose/eyes/ears at 12 inches and 48 inches. However, you can also think of the subject as a rock, trees, and a mountain and 12 feet and 48 feet. What I want you to see is that you move closer to or further from your subject the elements in the scene maintain their relationship between each other (nose/eyes/ears or rock/trees/mountain). No lens is going to change that relationship. If you switch from a 100mm lens to a 20mm lens without moving the camera, everything in the frame is rendered at 1/5 the size it was before. The relationship between those objects stays the same, but we see more of their surroundings.

At the top we see the camera to the nose is 12" and to the eye is 13" and it is 16" to the ear. When we pull back those numbers change to 48", 49", and 52". The tip of the nose to the ear in each situation remains about 4" and isn't going to change whether we're close or far away, or whether we use a short or long lens. What has changed is the yellow shaded area. Up close that 4" is relatively similar to the 12" camera distance. The ears are 1/3 again as far from the camera as the nose is. Moving back that relationship changes so that the ears are now relatively the same distance from the camera as the nose is (just 1/12 again as far). The further you move back from your subject the more pronounced the effect. Hence the appearance of "compression" or flattening of the view caused by backing away from your subject.

As noted, the same thing happens in landscape photography. Just substitute rock/trees/mountains for nose/eyes/ears. Move in close to an object and it becomes big in the scene and everything behind it starts to fall away in size. But if you back up far enough the relationship between the objects gets tighter (compressed). It doesn't matter if you have a short or long lens, the compression is the same. What the lens choice does is allows you to get more into the frame (short lens) or to zero in on a particular part of the scene (long lens).

If you stand in one spot and use a zoom lens the perspective stays the same. In many cases this is exactly what you want, and there is nothing wrong with that. But if you take the opportunity to move around your subject and change the camera to subject distance, whether with a prime lens or a zoom lens, you open yourself up to more variations and possibilities. Move in close to emphasize size differences and select a shorter lens to take it all in. Move back to de-emphasize size differences and select a longer lens to bring it all closer to you. You could use a short lens and get the same compression, as shown above, but that leaves you with tiny subjects that you will need to blow up to billboard size to recognize, with an inherent loss of quality.

You have probably noticed differences in the depth of field and overall image quality in the outdoor examples. I'll discuss that in a future post. For now, just start moving around and view things in different perspectives.

Then come back and let us know what you discovered in the comments below.


*I use a mannequin for these examples for a variety of reasons. One is that I can make sure the model doesn't move between camera setups. Another is that I hope the audience won't be distracted by the look of the model and facial expressions that might otherwise influence the look of the image.

**The short lens used in close was actually zoomed to 32mm. Oops! But it doesn't change anything about the lesson.


  1. Someone else who gets it...

  2. This is a real eye-opener, John. I tend to dislike the flatness in telephoto, yet am wary of introducing too much wide angle distortion getting close up. At any, it's making me explore wide angle, closer portraits now, which is probably closer to what I used to do before I started studying classic rules of portrait photography. I feel like I'm on a bit of an unlearning process, now.


Note: Only a member of this blog may post a comment.