[tig] FW: Tig digest - red LEDs

Schnuelle, Dave DLS
Mon Oct 4 21:13:55 BST 2004


Clint Koch at USL, one of the makers of red LEDs for film projectors, is
interested in your problem.  His approach is to replace the quartz lamp
with a red LED illuminator, as he has done for film projectors.  There
is no reason this should not work, as Dave suggests below.  In our
experience, a red LED with a cyan dye track gives the same levels as
white light with silver sound tracks.  The issue is the mechanical mount
to ensure the LED light is focused on the film sound track.  I've given
him your names as possible contacts who may be able to recommend someone
to work with at Thomson and Cintel to get red lamps for the telecines.
Sam Chavez is another good prospect, as Craig suggests.  I'd contact him
also to see if he wants to work on this.

Best regards,

Dave Schnuelle
Director, Image Technology
Dolby Laboratories, Inc.
3601 West Alameda Ave.
Burbank, CA  91505
Tel:  (818) 823-2800
Fax: (818) 557-0890
Email:  dls at dolby.com


Message: 7
Subject: RE: [tig] Cyan Dye Tracks
Date: Wed, 29 Sep 2004 23:49:35 -0700
From: "Nichols Craig" <Craig.Nichols at thomson.net>
To: "Dave Corbitt" <david.corbitt at verizon.net>,
   "Rob Lingelbach" <rob at calarts.edu>,
   "Telecine Internet Group" <tig at colorist.org>

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.



-----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

Re: utilizing Aaton or Evertz type scanners for Cyan auido tracks.=20
The whole question of scanning Cyan Dye tracks can be more simply=20
addressed by replacing the tungsten halogen bulb in the optical=20
exciter assembly with a bright strip of LEDs of similar light=20
emitting surface area as the glowing filament but limited to=20
approximately 660 nm wavelength. This would be much simpler and=20
easier to accomplish than all these complex schemes of reinventing=20
the whole assembly. Most of the optical audio sensor would not change=20
and there would be no need for it to change. The only different=20
characteristic needed to properly scan Cyan tracks is to complement=20
the Cyan Dye which absorbs visible Red (Cyan is "minus Red" in=20
subtractive color nomenclature) by providing a Red light source of=20
suitable wavelength. Contrast of the tracks is then optimized. And=20
the existing sensors are all in the right place for traditional sync=20
sound. On a Spirit the Keykode reader is way before the image gate.=20
Optical audio pickups are always after the gate to complement=20
industry practice for many decades. To delay the audio from a sensor=20
placed before the gate, you would have to add the number of frames=20
before the gate, and the number of frames after the gate, to delay=20
the audio sufficiently for sync sound. So Cintel and Thomson, how=20
about it? Can you come up with an alternate optical audio light=20
source upgrade for our expensive machines to get us all working with=20
these kinds of tracks? It shouldn't be that hard to do to replace a=20
light bulb with an LED array. Those ultra bright Red LEDs used in
new auto tail lights and traffic signals would probably do the trick=20
quite nicely.

Dave Corbitt
Post Logic NY

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