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Re: [OM] A shutter speed mystery

Subject: Re: [OM] A shutter speed mystery
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Sat, 10 Mar 2012 09:57:28 -0500
For those of you so inclined here is the entire 136 page "user's manual" 
for the 12-inch Mortar Model 1890MI.
<http://www.scribd.com/doc/17375868/TM-9456-12inch-Seacoast-Materiel-12inch-Mortar-M1890MI-Mounted-on-12inch-Mortar-Carriage-M1896MI-and-M1896MII>
All of the info about the various forms of ammunition is found on pages 
77-101 (according to the index)  :-)

Chuck Norcutt


On 3/10/2012 8:52 AM, Johnny Johnson wrote:
> Don't know the answer to your question Chuck but when I was there I was
> impressed by the sheer size of the projectiles and the range. If I remember
> correctly they were on the order of 3/4 ton each and had a range of seven
> miles with a maximum altitude of ~three miles. They didn't contain
> explosives, just depended on the weight of the projectile to do the damage.
>
> I do remember seeing the photograph that has you puzzled.  My only reaction
> was to think of how neat it was that they caught the projectile on film,
> not the technicalities of how it was done.
>
> Cya,
> Johnny
>
> ---------------------
> Johnny Johnson
> Cleveland, GA
> On Mar 10, 2012 8:00 AM, "Chuck Norcutt"<chucknorcutt@xxxxxxxxxxxxxxxx>
> wrote:
>
>> As a possible answer to my own question it occurred to me that the
>> projectiles (at only about 1/300 second after firing) are probably being
>> illuminated by the bright flash of the guns.  So the film was probably
>> exposed by the flash of the guns and not the ambient light.  Sort of a
>> built-in strobe and not requiring a fast shutter or fast film.  Sound
>> reasonable?
>>
>> Chuck Norcutt
>>
>>
>> On 3/10/2012 7:34 AM, Chuck Norcutt wrote:
>>> 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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