[Milsurplus] Arc Lamps for projector sets

[Sheldon Daitch]

Clete,

Oh yes, truly a fascinating mechanical device.

Sheldon

On 5/1/2012 3:02 AM, C.Whitaker wrote:
> 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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