Yesterday we went with some friends to Fort DeSoto Park for a picnic and
a bit of beach lounging. <http://en.wikipedia.org/wiki/Fort_Desoto>
While a very large public park today, Fort DeSoto was originally
constructed between 1898-1906 as a coastal defense battery to protect
Tampa Bay. If you scroll to the bottom of the page linked above you'll
see some of the artillery and mortars originally installed here and at
Fort Dade a short distance away. With 12" bores the mortars are rather
impressive beasts. They were first fired in 1903 and were deactivated
not later than 1917.
In a long corridor of historic photographs of the guns and emplacements
there is one very faded shot of two mortars being fired at the same
time. Much to my amazement the projectiles of both guns are clearly
visible perhaps some 30 feet above the muzzles. According to the
details I've been able to find about these guns the muzzle velocity
ranges from about 1,000 to 1,500 feet/second depending on the weight of
the projectiles whose length ranges from about 3-4 feet.
Now the shutter speed mystery. How was this photo taken? At 1/500
second the projectiles moving at 1,000 feet/second move 2 feet or 4 feet
at 1/250 second. The angle of view from the camera's position probably
creates some foreshortening of the projectiles but it *appears* to me
that the shutter speed would have been not longer than 1/250. I don't
know whether shutters of the period operated that fast but, even if they
did, I don't know how it would have been captured on a film emulsion of
the time.
So, how was this photo taken?
Chuck Norcutt
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