[Milsurplus] Arc Lamps for projector sets

[Sheldon Daitch]

John,

There were two adjustments, the framing control and
the shutter phase, two different adjustments.

I haven't touched a 35mm projector since maybe 1969,
so I have to go from memory, prodded with a Simplex XL
manual.

http://www.film-tech.com/warehouse/manuals/SIMXLINSTR.pdf

This manual shows the shutter timing control on the top and I
have to tell you, I just don't remember where it was.  The frame
control exactly where I remember it.

Page 4-9 has the shutter adjustment set up, and there is mention
of the shutter adjusting knob on page 1-25.

Thanks for making me take a trip back down memory lane.

73
Sheldon




On 4/30/2012 11:30 PM, J. Forster wrote:
> In fact, the whole Geneva mechanism rotated to make the adjustment. I
> think they were made by LaVezzi.
>
> "Frame !"
>
> -John
>
> ===============
>
>
>> 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
>>>>>
>>>> ______________________________________________________________
>>>> Milsurplus mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:Milsurplus at mailman.qth.net<Milsurplus at mailman.qth.net>
>>>>
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>>
>>>>
>>>
>>> ______________________________________________________________
>>> Milsurplus mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Milsurplus at mailman.qth.net<Milsurplus at mailman.qth.net>
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html