Tungsten VS Stobe (late and long)

[Donal Philby <donalphilby@earthlink.net>]

LUGnuts:  (I'm a little latebut just getting to some posts)

frederic wrote:
>>Question for the group.. .that is if you are still reading! I want to get
into Tungsten lighting & don't know much about the systems out there
apart
from their names:Arri, Lowel. I like to get the equivalent system of 2
strobe
monolights ?  Is that possible without having 10 lights? Can any one
inform
me on how much wattage I can plug into regular household current. Any
thoughts would be appreciated. <<

Frederic:

One time I had to photograph a Rail Gun, one of those electromagnetic
beasts with a whole building of capacitors to fire it.  Anyway the
technical challenge to do the photo made me learn some things that I
will try to write here.  Hope this is of interest.  Have faith, I will
talk about tungsten versus strobe.

The rail gun is about 25 feet long but when it fires you can't be within
a block of it.  Lots of electromagnetic radiation.  So cameras had to be
fired remotely.  The client also wanted the gun photographed while being
fired, and would only fire it once.  So picture had to be done in two
stages: first the unit strobe lit and then the actually firing double
exposed onto the film.

 I found there was a control room (like NASA) and fiberoptic controls. 
Plus they photographed the actual projectile with a Hulcher High Speed
camera.

Client wanted it shot 4x5.  I went to Granger's (a goldmine for the
putterer) and bought two washing machine selinoids.  I rigged these to
my two 4x5s and lenses and added cord to hook them to the same circuit
as the Hulcher (which would start and run for four seconds).  When 110
volts were applied, the selenoids closed, pulling the shutter release. 
Paper clips were used to connect selinoid and shutter.

So, went to the building with all my stobes and a studio partner's
stobes, about 15,000 watt seconds total.  We mounted the camera with
Bogen clamps to metal posts in walls of the building.  We setup strobes,
did tests, and then fired a couple sheets of film that I later had
processed as a check, plus two sheets of film in each camera,one
negative film, one transparency that were left in the camera.  Then we
packed all the strobes up and left cameras hanging for a week.

Meanwhile I had done some research on the Hulcher to figure what the
exposure would be of the muzzle blast and how to deal with the fact that
the gun would be fired with the big door of the building open in
sunlight.  The Hulcher runs at about 4000 to 6000 frames a second
(depending on exposure desired).  The lens was about f/5.6, I think.  I
can't remember all the details, but I figured that using a neutral
density glass from a welder's mask and shooting at f/22 for the four
seconds the Hulcher would run, I could capture the actual blast properly
exposed (it was that much brighter than daylight).  The selinoids would
open the lenses when the Hulcher was started and close (on "B") when the
camera ran out of film.

So here is where we get back to tungsten vs. strobe:

Basically, what I discovered by implication while figuring the exposure
from reverse engineering the Hulcher exposure (and what photographers
with more technical education probably know) is that power in watts (not
watt seconds) of strobes is the inverse of the flash duration.  My
Balcars fire on full power at 1/500 of a second.  Each P-system head is
1600 watt seconds.  So to get a tunsten light with the intensity
equivalent to allow me to photograph at 1/500 of a second would require
the inverse:  1600 x 500 or 630,000 watts.

Consider:  If I have on 1600 watt tungsten Lowel, for instance, that
gives me an exposure of 1 second, I would need two side by side to
reduce the exposure to 1/2 seond and four to reduce exposure to 1/4.  To
allow me to shoot at 1/500 of a second I would need 512 of them (9
stops).  Maybe I'm a bit off on this, but I think this is accurate.

Of course, no one would use 500 lights.  The tungsten shooters use long
exposures instead.  But this does give one an appreciation of just how
much power and convenience is packed into one studio strobe.   Now
figure just what a 50WS Metz stobe firing at 1/1000 sec would take to
duplicate with tungsten.

As for the rail gun photo, it went off as planned except that one camera
didn't fire.  I got the image on negative, converted to transparency and
delivered to client.  They were ecstatic and said even the color of the
smoke and the gradations were accurate.  I had $2500 at stake to pull it
off. 

I earned it.

Donal Philby
Seattle (temporarily)