This is obviously a high frame rate photo of a very close cycling race finish. What gets me is not the closeness of the race (although the closest I've ever seen). Rather, it's how the spokes appear to bend, including "displacement" of the drilled holes in the wheel. I find it extremely unlikely this is actually happening in real life (quantum physics anyone?). Can anyone explain what's going on here photographically? It reminds me of how sometimes spinning airplane propellers are distorted in some photos I've seen.

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Photo-finish photographs are made using slit-scan cameras, not conventional cameras. The left to right relationships in the image are temporal rather than spatial...the distance in the image between the front and the rear of each bicycle reflects the amount of time between the front and the rear of the bicycle crossing the finish line (and passing in front of the slit).

The bending of the spokes reflects the different times at which the spoke crossed the finish line and was captured through the slit. The entirety of the hub of the wheel crosses the line in a shorter amount of time than the circumference of the wheel.


Of course the spokes are not bending. It is an effect of (mostly) focal plane shutters. These take perhaps roughly 1/3 of a second for the shutter opening to move across the frame (speaking 35 mm film). Faster shutter durations are implemented by a second curtain following closely behind, closing the shutter opening after the measured delay. So a 1/4000 second shutter is implemented by a 1/4000 wide open slit moving across the frame in about 1/3 second.

Most focal plane shutters today move across the short frame dimension (faster). My guess (just my guess) is that this one was an older shutter (old camera, not the picture, 30 years or more) that still moved horizontally, left to right as we see it. Speaking of bottom half of the wheel, the outer end of the spoke was captured earlier in time than the inner end, so it appears curved after the wheel rotated more (shutter slit moved right).

The early classic example of this effect is 1912 picture by Jacques Henri Lartigue.


It is why cartoons show race car wheels as elongated ovals to indicate speed.

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    I'm no expert on this, but it seems to me your answer should be treated as no more than (incorrect) guesswork, if @ben's information is correct (which it presumably is) – osullic Aug 27 '17 at 18:50
  • The effect in both is the same, the fast shutter speed in essence creates a slit scan shutter. – ths Aug 27 '17 at 20:22
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    Right, this "slit" is exactly the same thing as a focal plane shutter (used in most SLR and DSLR today). Here's an article explaining it's the same thing, which even includes the same classic Jacques Henri Lartigue photo. people.rit.edu/andpph/text-slit-scan.html Concept is nothing new, the photo is 1912. – WayneF Aug 27 '17 at 22:58
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    I'm not sure where you get 1/3 of a second from. Most modern cameras have x-sync speeds faster than 1/200th of a second, so the leading curtain has to move at least as fast as that. – BillDOe Aug 28 '17 at 0:02
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    1/3 second is several orders of magnitude too slow for any modern focal plane shutter. Curtain transit time for most FF cameras are around 1/300 second and for most APS-C cameras around 1/400-500 second. The transit time must be shorter, not longer than the flash sync speed. – Michael C Aug 28 '17 at 3:57

The motion in accordance with the shapes and how our eyes perceive them makes for the formula of an optical illusion. The numbers and the measurements have to be specific and precise. Everything does.

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    I don't think this is an optical illusion. Our eye isn't being tricked in this photo. It's the way the image has been captured. I don't understand what you mean by the measurements having to be specific and precise. – MikeW Aug 28 '17 at 2:25
  • This answer says a lot, without really saying anything. "Everything has to be precise" is a meaningless statement, without more context or specificity. – scottbb Aug 28 '17 at 13:06
  • Everything is precise from the rotation to the revolution of the planets to the wind to every tree, every leaf, to every day that's warm cold the degrees that measure those days. Everything in life is married to Precision. It is always important in every situation no matter how small or insignificant it may seem. Precision is always there in every instance and if it became meaningless we would all die. – user67954 Aug 28 '17 at 13:34
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    @user67954 - he isn't saying precision is meaningless, he's saying that your statement about precision, without specifying how it relates to the question, is meaningless as it doesn't actually answer the question. It would be like if I answered that "it has to do with photography". Sure, it may be an accurate statement, but it also doesn't inform the person asking the question of anything without further explanation, therefore it is a meaningless answer. – AJ Henderson Aug 28 '17 at 14:28
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    this is not a philosophy forum. – ths Aug 28 '17 at 14:34

That is funny because it is spoken in In such a way that it is extremely vague and it's almost like answering the question without having to answer it. Yet at the same time you have a series of conditions of things that come together in concern with the way that light behaves in relation to matter and how we perceive it. all these are elements that are coming together that are taking place to create this perception unless it is a (bending of matter) which I don't believe that it is but you however want to believe that some phenomenal extraordinary event took place on that day because to you that would be more interesting

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    This is utter nonsense. – Caleb Aug 28 '17 at 13:51

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