[tig] Cyan Dye Tracks

Nichols Craig Craig.Nichols
Thu Sep 30 14:33:06 BST 2004

Hi Dave,

Some manufacturers have experienced hum problems when introducing LED readers to projectors.  Perhaps there are more nasty magnetic fields, very bright stray light present, or perhaps the pickups are not selective enough to deal with only red light, but I honestly don't know.  If someone can just use existing pickups and an LED on an existing telecine pickup, then by all means, they should try and report back if they have success. I would wish them all the luck in the world, and hope they succeed, because I always liked simple better.  ;-}  On Dolby's website, there used to be several articles about the virtues, advantages, and benefits of reverse scan led readers.  I have not looked recently.  Perhaps there is more at www.dyetracks.org.  

Disclaimer.. I work for Thomson.  Thomson welcomes others to try different methods to reproduce cyan tracks but Thomson, or I do not assume any liability or risk for anyone's attempt to do so.

Craig Nichols
Senior Technical Service Engineer 
DFA Film Products
Thomson Broadcast Media Solutions
craig.nichols at thomson.net 

-----Original Message-----
From: Dave Corbitt [mailto:dcorbitt at postlogic.com]
Sent: Thursday, September 30, 2004 5:22 AM
To: Nichols Craig; Telecine Internet Group
Subject: RE: [tig] Cyan Dye Tracks
Hi Craig,

Why would LEDs produce more hum than unfiltered Tungsten lamps as the 
optical exciter?
Hum is a signal to noise issue. If the light source is too 
dim and the gain has to be cranked up on the sensors, then hum pickup may 
become an issue from ambient light or magnetic fields. But the new ultra 
bright LEDs are VERY bright and should provide at least as much light 
energy as the white light of the traditional tungsten bulb if designed 
properly. More light = more signal = better signal to noise ratio. Its an 
engineering problem and probably not a difficult one. I think 
re-engineering the entire assembly and placing the LEDs on the other side 
(in the capstan groove) would be a difficult and costly design and of no 
obvious improved result. Good frequency response has been achieved with top 
side exciter assemblies for a long time. Ideally, the lamp should be on the 
emulsion side for best resolution of fine detail within the optical track. 
Print material is normally "emulsion side up" on today's (and yesterday's) 
telecines and Cyan optical tracks are a release print issue. Changing the 
light source is relatively simple IMHO. Thomson? Cintel? We know you are 
listening. Can we hear from you on this issue? What are you planning to do 
and how much will it cost?

Dave Corbitt
Post Logic NY

At 02:49 AM 9/30/2004, Nichols Craig wrote:

>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.

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