Face distortion is not due to lens distortion

Here is a series of photographs of my face, taken from different distances, using lenses with different focal lengths (see here and here for more examples). Because I covaried distance and focal length, my face appears about the same size in each image. However, the relative size and positions of my various facial features changes very markedly – in the last photo I have no ears! Why does this happen?

Photos of me using different focal length lenses (85-8mm on an APS-C sensor, so equivalent to 127.5-12mm on 35mm film) from five different distances (200-20cm). Note that the wide angle lens used for the last three photos is not a fisheye lens (it’s one of these).

Many people would probably tell you this was due to ‘lens distortion’ – implying that the wide angle lens used for the photos on the right somehow distorts reality, creating an imperfect image. This is totally incorrect. Actually, the only ‘distortions’ are caused by geometry, they are nothing to do with the lens or the camera.

In the leftmost image, the subject is far away (2 metres) from the camera. At this distance, each of my facial features is a similar distance from the camera – within a few percent of the total distance – so my face appears flat. In the rightmost image, I’m about 20cm from the camera. Because my nose is about 10cm away from my ears on my head, this means that there is a large proportional difference in the distance from the camera to my nose, and the distance from the camera to my ears. My nose appears much larger, because it is proportionally closer to the camera than the rest of my face.

The crazy thing about this is that it happens in real life too, we just don’t often notice it. If you look at yourself in the mirror from very close up (or get close to someone you’re intimate with), you get exactly the same distortions (closing one eye helps with this, as most people can’t maintain vergence that close). I find the middle image above to be the closest to how I think I look, probably because the distance of 40cm means it’s approximately what I see when I look in a mirror normally. Portrait photographers usually use long focal lengths (at least 85mm) because this is thought to produce a more ‘natural’ and flattering portrait.

All of this is important, and not just to make yourself look hot on Facebook (a hint ignored in both those links: don’t get too close to the camera!). Every time we go through passport control at an airport, the photo on your passport gets compared to the real life you, by someone who never met you before. Similarly, if you ever end up in court for something, CCTV evidence – usually shot from many metres away – might be used to identify you. It turns out that people are surprisingly bad at correctly identifying strangers in this way (e.g. see this paper). I wonder how many false convictions this has resulted in over the years….

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13 Responses to Face distortion is not due to lens distortion

  1. Anon says:

    I saw a poster at a conference a while ago that was studying this (or, more precisely, they were studying the effect those distortions had on social judgments of those faces)–I think they published their results in PLoS One recently.

  2. rika says:

    Makes alot of sense, but isn’t there a lens distortion-effect also?
    Check this out; http://verybadfrog.com/36785/photo-stories/how-camera-lies-lens-distortion-portraits

    • Bill says:

      No, that’s not the lens, that’s the proximity effect. However, the idea that the lens is the cause is frequently repeated and is firmly in people’s heads.

  3. david says:

    Why did you not photograph your face from the SAME distance with different lenses? Then you would have seen that ALSO the lense size has an effect on the picture. Incorrect article.

    • bakerdh says:

      Hi David. Yes, that’s a good idea, I might try it sometime.

      • Corwyn says:

        Do. You will discover that David is mostly wrong. Lenses are admittedly not perfect and will give you some distortions, but if those distortions were large the lenses wouldn’t sell (excluding fisheyes, and other lenses *intended* to be distorted)

    • Bill says:

      David, I assume that by “lens size” you mean focal length. Yes, changes in lens focal length will change the field of view and the apparent sizes of subjects within the photograph.

      However, using different lenses in the same position relative to the subject, you will always get the same geometry of viewing and thus the same perspective, even if the field of view and apparent size of the subject both change due to using a different lens.

      That’s not the same thing as the distortion caused by perspective as you move closer to the subject to compensate for the angle of view of a wide-angle lens. You get very different distortions with different lenses precisely *because* of the photographer compensating by moving the camera, thus changing the perspective.

      In other words, it’s not using a different lens that changes the perspective and causes distortion, rather it’s the lens enticing the photographer to change the perspective to get the framing that he wants, and that action by the photographer then changes the distortion.

  4. […] There’s also the technical issue of our close-range camera phone lenses distorting our faces. […]

  5. […] There’s also the technical issue of our close-range camera phone lenses distorting our faces. […]

  6. […] There’s also the technical issue of our close-range camera phone lenses distorting our faces. […]

  7. […] on the left, then I would propose that the helmet is inaccurate. Here is an additional read: http://bakerdh.wordpress.com/2012/05…ns-distortion/ Okay, let's get back on-topic. Last edited by CSMacLaren; 1 Day Ago at 12:50 […]

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