"Bob Harrington" wrote in message
...
Michael Huber wrote in news:fnhpoe$2pq$00$1
@news.t-online.com:

John Smith wrote:
Are you actually seeing the prop blade "bent" forward, or simply
interpreting the blade pitch as the prop being bent forward?

I would say they look bent forward, especially the lowest one.

I believe what you are seeing is an artifact of the camera shutter. Most
camera shutters that lie on the film plane (just above the film) consist
of a pair of horizontal or vertically moving curtains that are spring
loaded to zip across the film to make the exposure.

It takes a small, but not infinite, fraction of a second for each curtain
to cross the distance; they are timed so that each particular point on the
film receives light for the desired time, but with very short exposures
under bright conditions such as a sunlit sky, this results in the actual
distance between the leading and trailing shutter curtains being very
small, much smaller than the width of the film.

In effect, there is a narrow slit that moves across the film exposing it
as it goes. While the shutter speed may be set to only 1000th of second,
it could well take ten times that long for the slit to cover the full
frame of film. If something in the scene like a propeller is moving very
quickly, it can move visibly during that time, resulting in the apparent
warping of the propeller.

Older cameras especially can show this effect, as their shutters move more
slowly than most modern cameras.

It also depends on the line of travel of the focal plane shutter. Earlier SLRs
had shutters that traveled horizontally and produced the effect. In the '70s
the trend was to vertical travel shutters; these significantly reduce the
phenomenon and allowed an increase in shutter speed with the shorter distance
to cross. The effect varies according to the direction of flight of the target
and the direction of travel of the shutter. It can be particularly pronounced
when one compares race cars; they can appear significantly longer or shorter
depending on how they cross the field of view.
--
Andrew Chaplin
SIT MIHI GLADIUS SICUT SANCTO MARTINO
(If you're going to e-mail me, you'll have to get "yourfinger." out.)