[Milsurplus] Arc Lamps for projector sets

[Sheldon Daitch]

John,

Yea, I am sure the strobbing might very well be a factor.

The Simplex XL heads had a double flash shutter, that
is, the film stock was illuminated twice during the time
the film was stationary in the film gate, then when the
rotary shutter closed the light path, the Geneva movement
advanced the film one frame.

Oh, the word "phase" reminded me of one adjustment on
the Simplex XL heads, there was a shutter phase adjustment.
It changed the phase of the shutter with the Geneva movement,
to eliminate travel ghosting.  If the shutter opened before the film
settled to a full stop, or the shutter was not closed before the
film started to move, there would be a slight ghosting from the
film movement.  

Interesting. I had not thought about that adjustment in damn close to
40 years.

Here is some commentary:

http://www.film-tech.com/ubb/f1/t005504.html

73
Sheldon

On 04/30/12, "J. Forster" <jfor at quikus.com> wrote:
> 
> On the topic of carbon arc lamps, I believe it is easier to make an arc
> lamp to run on DC than AC.
> 
> The DC electrodes are different, positive and negatice. The AC electrodes
> are the same for both.
> 
> I think movie projectors use DC to avoid strobing effects, because the
> projector has a shutter that is closed while the film advances. In the US
> that is 24 per second, and has common factors w/ 60 Hz.
> 
> Even using filtered DC there is some strobing and the projector has a
> mechanical differential to adjust the shutter phase.
> 
> -John
> 
> ====-
> 
> 
> 
> > Way back, when I was still in high school, I worked in
> > a theater which used carbon arc lamps but we had
> > a motor generator which provided the DC for the arc lamps.
> >
> > I am almost positive the lamps were made by Peerless and
> > very similar to:
> >
> > http://www.flickr.com/photos/combatcamera44/6103931423/in/photostream/
> >
> > 73
> > Sheldon
> >
> > On 4/30/2012 5:57 PM, Richard Solomon wrote:
> >> Most of the Movie Theatres in Downtown Boston used DC for the Arc Supply
> >> on
> >> their projectors. Copper coated Carbon rods were used.
> >>
> >> BTW, anyone remember the War Surplus store next to the old Radio Shack
> >> on
> >> Washington Street ? Just outside Scollay Square.
> >>
> >> 73, Dick, W1KSZ
> >>
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