Hi Andy:
Notice that the interesting lines in each image are perpendicular to
the short side of the frame.
Second, the outer edges of the lines form the circular path of the
propeller tip ( adjusted for angle of course ).
So, it seems that the camera sensor is being scanned across the
image parallel to the short side of the frame.
For a few microseconds, the image of the ground is clearly seen and
then for a fewer microseconds, the propeller's black color blocks the view.
And so on.
The really interesting thing here is that the scan rate is almost
exactly in synch with the propeller radial rate, a happy coincidence
that yields almost straight lines
for the portions of the image either showing the propeller ( black
lines ) or the landscape.
The really interesting question is can you infer the scan rate of the
camera given the propeller RPM?
Nice puzzle,
James
At 03:24 PM 9/24/2008 -0400, you wrote:
Hi,
I was given a sample of some photographs taken of the propeller
of an airplane made with, I believe, a phone camera. There is an
obvious anomaly present. Although I suspect the reason I am not
really sure (really I do not know!) how this came about. If you
can shed some light on the effect for me it would be much appreciated.
See the images here:
http://people.rit.edu/andpph/a-misc/phonecamera-prop-effect-1.jpg
Thank you for taking the time to give me a hand!
cheers,
andy
James Schenken
