These pictures were shot by a friend of mine who was flying a two ship formation with another SF-260EA. The images are beautiful but what make them more interesting is that the propeller blades look bent in both pictures. Is the aircraft flying with a damage propeller or is it an odd effect of taking a picture with a cell phone camera to a high speed rotating object? Obviously, the correct answer is the second one (in fact, Roberto and his wingman landed without any problem with the propeller in perfect shape…), but is anybody able to explain why the phone camera produces such oddities?
I’ve flown with the SF260 in the past and took many pictures using professional cameras and none gave the same results (read here and here).
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.
The answer lies in the type of shutter. I am not sure of the correct english word but I think “curtain shutter” would be the best. Such shutters operate in vertical or horizontal way (the aperture is travelling sideways or vertical). So at certain shutter speeds, the image is taken step by step sideways and due to high speed propeler, it appears bended on the photo. Here’s even more radical photo of this phenomena of our AF Cougar helicopter:
Thank you very much. I’m extremely happy to receive such a quick feedback to a “technical question”!
Dear Mr. Cenciotti,
You can find in the followinf url a couple of heavily distorted airplane images caused by the same scanning phenomenon occured on digital camera sensors.
Ciao e a presto.