[Milsurplus] Arc Lamps for projector sets

[C.Whitaker]

de WB2CPN
Sheldon,
Something interesting, and perhaps because of its
age, is the way the Geneva movement advanced
the film. It was a study in rotary-to-linear motion.
73  Clete
++++++++++++++++++++++++++++++++++++


On 4/30/2012 4:13 PM, Sheldon Daitch wrote:
> 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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