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.

Thanks!

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*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.

More On Aperture and DOF

This is a follow up to my recent post about the effect of aperture on the look of a portrait.

There, I mentioned that changing focal length would not affect the depth of field if the camera was moved to maintain the size of the subject in the frame. I didn't have any images prepared then to demonstrate this at the time. I got a chance to create those images last night and present them here. Click on each image to load a larger version that will be easier to study.

 Above we see three photos that were taken with 135mm, 85mm, and 35mm lenses all set to f/2.8. The camera was moved closer with the 85 and even closer with the 35 to make the mannequin head be about the same size in each. If you look closely you will see that the depth of field is about the same in each. The perspective is different in each because the camera was moved (not because of the lens change).

Many photographers go for a lens in the 85 to 105mm (full 35mm frame) range for portraits because they put you at a distance from your subject that gives a nice drawing to the face with pleasing relationship between the features on the face and head (nose, mouth, eyes, ears). If working with a smaller sensor camera look for lenses with similar angles of view for that format (such as 50-65mm on cameras with a 1.5 or 1.6x multiplier).

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In the second set of photos everything is the same as the first set, except that the aperture was set to f/22. Again, you can see that the depth of field remains the same, even though various focal length lenses were used (135, 85, and 35).

You may also be surprised to see that the face looks the thinnest in the image taken with the wide angle lens. This is what happens when you move in close. With any lens the objects closest to the camera appear larger than objects further away. When in so close with a short lens the nose is relatively closer to the lens than the cheeks, eyes, and ears. So they fall away and look smaller. When you move back with the longer lens the nose, eyes, and ears are all relatively closer to each other than to the lens, so the face flattens out and they all appear at a similar size. This is due to the camera to subject distance, not the lens, even though this is often erroneously called "telephoto compression." See the fourth set below for more about that.

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In this third set of photos the camera remained stationary. The top image was taken with an 85mm, the middle is 135mm, and the bottom is 35mm. Here we can see that the size of the mannequin head is very different between the images and the depth of field changes drastically between because of the difference in magnification from each lens (all set to f/2.8)

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In this final group we again have images taken with the 135mm, 85mm, and 35mm lenses, this time all set to f/5.6. As in the third set, the camera remained stationary and the lenses were changed.

In these last two sets of images you should be able to see that the perspective remained the same even though the lenses were changed. The relationship between the head and the background is the same in each. If you cropped in on the 3rd image in this set the perspective would match the 1st image in this set. But the depth of field is different. Remember that when the camera to subject distance is set and the lens is changed the perspective of the area of the image that is common to each image is the same. The camera to lens distance determines the perspective. The focal length determines what fits into that frame.

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One of my favorite Ansel Adams quotes is "good photography is about knowing where to stand." I think that many people misunderstand this quote. They might associate it with Jim Richardson's quote "if you want to be a better photographer, stand in front of more interesting stuff."  But what I believe Ansel meant was that you need to find the location to set up the camera that gives you the perspective (relationship between items in the scene) that you want, and then you select a lens focal length that fills the frame the way you want. Too often people pick the lens first.

I really don't like the mantra of "zoom with your feet." Zooming implies making the scene smaller or larger while maintaining the perspective by changing focal length without moving. If you move your feet the perspective changes. So you CANNOT zoom with your feet. I'm not saying it is a bad exercise to select one prime lens and learn how to use it by moving around. If you want to make good and interesting photos, do find your location by moving your feet, but then select the appropriate lens to fill the frame of your camera. Maybe the frame should be "move your butt!" And a zoom lens is the perfect lens for this, as you can frame exactly as you want. Zoom lenses got a bad reputation in the 1970s when the quality wasn't nearly as good as prime lenses. Zoom lens design has come a long way since then and today's zooms come very close to the quality of prime lenses. That said, I often use prime lenses instead of my zooms, but this is primarily because of the weight of a good zoom. The primes are easier on my shoulder, elbow and wrist.

One more thing. Something that I learned during the exercise of preparing this article is that it really is difficult to manually focus a wide angle lens. I've always heard that short lenses were more difficult to focus, but it reallyshowed here. The following set of images were taken with the same camera/lens (35mm at f/2.0) combination. A was manually focused through the viewfinder. B was manually focused using Live View at 10x, and C was autofocused. Maybe autofocus isn't such a bad idea....