[tig] Cyan Dye Tracks

Nichols Craig Craig.Nichols
Thu Sep 30 07:49:35 BST 2004

Red LEDs, or Lasers, are what is used most to scan cyan tracks, since tracks are minus red, and are easily read by 660 nm light sources.  When I was investigating ways to read these tracks (before my employment by Thomson) I was told by various Red Reader manufacturers that their concern for replacing the existing lamp with LEDs had to do with the distance of the pickup from the film and the pickup sensitivity.  One potential problem with Red Led readers is pickup of stray hum, or so I am told. I was told by several manufacturers and by Dolby that the optimum approach is to shine led from the reverse side and collect the light on top of the film.  This approach can also imrove performance of legacy silver sound tracks.  Such reverse scan led readers have been in use on projectors since around 1997.  It might be possilbe to replace the existing lamp with an LED and have it work.  I have researched this area in the past, but have not done any experiments.

Sam Chavez from Bay Area Cinema Products is interested in discussing this.  He has produced custom readers for THX and others, I am told. This address is on the Dyetracks. org page under manufacturers. I cannot endorse any one particular vendor.

"If they build it someone will come"  opps wrong movie....

Again, Thomson disavows any knowledge of my actions.  Opinions are mine alone. I offer no warranties or guarentees of success with adding optical sound, and neither does Thomson.



-----Original Message-----
From: tig-admin at tig.colorist.org [mailto:tig-admin at tig.colorist.org]On
Behalf Of Dave Corbitt
Sent: Wednesday, September 29, 2004 4:27 PM
To: Rob Lingelbach; Telecine Internet Group
Subject: Re: [tig] Cyan Dye Tracks

thanks to Flying Spot Film Transfer for supporting the TIG.
Re: utilizing Aaton or Evertz type scanners for Cyan auido tracks. 
The whole question of scanning Cyan Dye tracks can be more simply 
addressed by replacing the tungsten halogen bulb in the optical 
exciter assembly with a bright strip of LEDs of similar light 
emitting surface area as the glowing filament but limited to 
approximately 660 nm wavelength. This would be much simpler and 
easier to accomplish than all these complex schemes of reinventing 
the whole assembly. Most of the optical audio sensor would not change 
and there would be no need for it to change. The only different 
characteristic needed to properly scan Cyan tracks is to complement 
the Cyan Dye which absorbs visible Red (Cyan is "minus Red" in 
subtractive color nomenclature) by providing a Red light source of 
suitable wavelength. Contrast of the tracks is then optimized. And 
the existing sensors are all in the right place for traditional sync 
sound. On a Spirit the Keykode reader is way before the image gate. 
Optical audio pickups are always after the gate to complement 
industry practice for many decades. To delay the audio from a sensor 
placed before the gate, you would have to add the number of frames 
before the gate, and the number of frames after the gate, to delay 
the audio sufficiently for sync sound. So Cintel and Thomson, how 
about it? Can you come up with an alternate optical audio light 
source upgrade for our expensive machines to get us all working with 
these kinds of tracks? It shouldn't be that hard to do to replace a 
light bulb with an LED array. Those ultra bright Red LEDs used in some 
new auto tail lights and traffic signals would probably do the trick 
quite nicely.

Dave Corbitt
Post Logic NY

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