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Here is the picture

enter image description here
Source:(brians-travels.com)

This looks like a photoshopped picture, but I believe it isn't. Is this some kind of strange occurrence that occurs only with the human eye? The blade on the top looks bent downwards. I can't figure out what happened in this picture. And will your picture look like this every time you take a picture of a fast moving propeller?

mins
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Ethan
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    This is more a digital photography question than an aviation one, but check out the top google results for 'propeller blade weird camera' to learn more about what's called a 'rolling shutter'. – egid Sep 30 '15 at 23:10
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    That happens more since the global warming has started, therefore it must be a metal softening effect of higher temperature. – mins Oct 01 '15 at 05:39
  • @mins it has to do with how fast the blades are spinning. Your not going to get much metal softening because the temperature has only went up 1.5 degrees. That does have a huge effect on crops and glaciers. – Ethan Oct 01 '15 at 11:51
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    I don't think this question should be closed, there are enough people out there who do not know what a rolling shutter is, and might think prop blades bend in flight. – falstro Oct 01 '15 at 13:50
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    You should ask this picture on Photography.SE (if it hasn't been asked already), this really is a camera question not an airplane question. – Jae Carr Oct 01 '15 at 14:46
  • @falstro Good point, makes me wish we could move this questions over to Photography.SE and still have it linked here... Is that possible? – Jae Carr Oct 01 '15 at 14:46
  • "strange occurrence that occurs only with the human eye" - no. The human eye is good enough to not see this effect. This "strange occurrence" only happens with relatively inexpensive cameras. Specifically CMOS cameras (all consumer cameras, most prosumer cameras and a small number of pro cameras). If you were to take a picture with a CCD camera you wouldn't see this effect. – slebetman Oct 05 '15 at 03:34
  • @Ethan Mins was joking. Hence the link to Wiki:Correlation does not imply causation. – reirab Oct 05 '15 at 04:10
  • At this point, over a year later, and with a perfectly reasonable answer, why are we trying to close this? I admit it's questionable, I said so above, but you might as well just leave it now. – Jae Carr Apr 20 '16 at 22:53
  • @JayCarr my suspicion is that, as we have done in other cases, if the answer is about aviation, we leave it open, else we close it. – Federico Apr 21 '16 at 06:36
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    This is a good, aviation related question, and appropriate for this SE. It just so happens that the answer has to do with camera mechanisms, not propeller design. – J W Apr 21 '16 at 10:19

3 Answers3

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It's an artifact of how a digital camera downloads captures the image from the sensor called rolling shutter.

Essentially the image is captured a single line at a time and the fast moving propeller changes location between each line captured.

Wikipedia has a nice diagram showing what happens step by step:

enter image description here

On our sister site photography.SE has a question asking about it.

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ratchet freak
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6

This is a result of the way the camera shutters operate. Usually, the cameras don't capture images in the same way as human eye i.e. they don't take image of the whole scene simultaneously but rather 'scans' horizontally or vertically. In normal cases, this rolling shutter method is not a problem, but can cause issues when the object is moving at high speeds.

Quote from user FGK:

The plenomenon is due to Rolling shutter (also known as line scan) is a method of image acquisition in which each frame is recorded not from a snapshot of a single point in time, but rather by scanning across the frame either vertically or horizontally. In other words, not all parts of the image are recorded at exactly the same time, even though the whole frame is displayed at the same time during playback. This in contrast with global shutter in which the entire frame is exposed for the same time window. This produces predictable distortions of fast-moving objects or when the sensor captures rapid flashes of light.

Rolling shutter

Source: ephotozine.com

In other words, it is due to camera rather than the propeller blades themselves. The effect of a simulated rolling shutter on a spinning disc shown below:

Rolling shutter

"Rolling shutter effect" by Cmglee - Own work. Licensed under CC BY-SA 3.0 via Commons.

aeroalias
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  • Note that this only affects digital cameras. Film cameras with physical shutters actually do capture the entire scene simultaneously. – reirab Oct 01 '15 at 02:51
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    The same happens on mechanical shutter, that's why traditional cameras had two flash synchronization modes, one by the "first curtain", one by the "rear curtain". The effect appears different, but is actually the same at a slower speed. – mins Oct 01 '15 at 06:13
  • @reirab: For certain values of "simultaneously", which is to say "no, not really". Shutters do not move infinitely fast. – Nathan Tuggy Oct 04 '15 at 21:35
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    @reirab: Not all digital cameras, only CMOS cameras. CCD cameras capture the entire scene simultaneously (even more "simultaneously" than mechanical cameras) – slebetman Oct 05 '15 at 03:37
  • @NathanTuggy I meant that film cameras (with physical shutters) don't scan the image pixel by pixel, not that the shutter is infinitely fast. While the shutter is open, the film is being exposed to the entire scene with a film camera, regardless of shutter speed. As far as I can tell, the link in mins' comment is just talking about whether the flash fires at the beginning of the exposure period or the end of it (which will determine where unlit objects in the scene appear vs. lit objects, like in the train/headlight example in the answer.) – reirab Oct 05 '15 at 04:05
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    @reirab: As the shutter(s) move across the film, you get effectively the same problem as here: the time between exposing different sides of the film is non-zero, so this problem can occur. (This principle is, I believe, also the same one that underlies the use of continuous film strips to capture a continuously viewable camera shot of a race's finish line, which shows in chronological order the finishers, despite only ever focusing a narrow vertical strip of light on the film at any one time.) – Nathan Tuggy Oct 05 '15 at 04:12
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This is an effect produced by the digital camera that took the picture. The CMOS sensor "scans" the picture from one edge to another, possibly bottom to top in this example. Each line of the photo is taken at a slightly different time, and the prop moves fast enough that it moves a little bit in between each scan line. After the camera puts all the scan lines together into an image, you can get the effect you see here.

You can read more about this effect at Rolling shutter.

Greg Hewgill
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