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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?

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    $\begingroup$ 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'. $\endgroup$
    – egid
    Sep 30, 2015 at 23:10
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    $\begingroup$ That happens more since the global warming has started, therefore it must be a metal softening effect of higher temperature. $\endgroup$
    – mins
    Oct 1, 2015 at 5:39
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    $\begingroup$ 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. $\endgroup$
    – falstro
    Oct 1, 2015 at 13:50
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    $\begingroup$ 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. $\endgroup$
    – Jae Carr
    Oct 1, 2015 at 14:46
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    $\begingroup$ 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. $\endgroup$
    – J W
    Apr 21, 2016 at 10:19

3 Answers 3

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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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    $\begingroup$ Another interesting exemple. And a another strange flying blade. $\endgroup$
    – mins
    Oct 1, 2015 at 6:02
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    $\begingroup$ @mins That second one is just a standard aussie prop. $\endgroup$
    – falstro
    Oct 1, 2015 at 13:45
  • $\begingroup$ The same thing used to happen with the focal plane shutters in many film cameras, for the same reason -- I've seen photos from the 1940s with similar (if slightly less pronounced) apparently blade curvature. $\endgroup$
    – Zeiss Ikon
    Aug 29, 2018 at 14:36
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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.

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  • $\begingroup$ Note that this only affects digital cameras. Film cameras with physical shutters actually do capture the entire scene simultaneously. $\endgroup$
    – reirab
    Oct 1, 2015 at 2:51
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    $\begingroup$ 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. $\endgroup$
    – mins
    Oct 1, 2015 at 6:13
  • $\begingroup$ @reirab: For certain values of "simultaneously", which is to say "no, not really". Shutters do not move infinitely fast. $\endgroup$
    – Nathan Tuggy
    Oct 4, 2015 at 21:35
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    $\begingroup$ @reirab: Not all digital cameras, only CMOS cameras. CCD cameras capture the entire scene simultaneously (even more "simultaneously" than mechanical cameras) $\endgroup$
    – slebetman
    Oct 5, 2015 at 3:37
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    $\begingroup$ @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.) $\endgroup$
    – Nathan Tuggy
    Oct 5, 2015 at 4:12
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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.

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