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Author Topic: Low cost homebrew red LED light source for cyan tracks Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-16-2003 01:19 PM                     The reasons why I took on this effort were: 1. I just have a home setup and use only analog sound. 2. To be prepared to read the new cyan analog tracks. 3. Don't have much $ to spend. (also can't afford a commercial jaxlite or reverse scan reader, either) 4. I like tinkering. 5. Figured there might be others with home setups in same boat as me that needed this contraption. Someone asked about color: I purchased this from a guy who sells LEDs at electronic flea markets. He called it "red" so that's all I can tell you about the color. I don't know the specific part number. Answering another question: Yes, additional wires and other "stiffening" could be added if a person felt that microphonism was a problem. [ 08-16-2003, 02:26 PM: Message edited by: Jeff Stricker ]  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 08-16-2003 04:18 PM                       You did good, Jeff! Cyan not withstanding, reverse scan is inherently noisier, being very sensitive to scratches on the film. (Anyone remember running older prints on Century R4s? Sounded like a rainstorm!)  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 08-16-2003 05:11 PM                  Jeff, adding to what Tim said, you have great enthusiasm, ingenuity, and enterprise! Don't get discourage or let the naysayers get to ya! >>> Phil  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-17-2003 02:51 AM                       I differ with Tim Reed's statement regarding reverse scan being inherently noiser than front scan. The Century R4 was truly awful but a better example of reverse scan done pretty well was the Norelco AA11 and even better, the early Western Electric reverse scan soundheads. The reason reverse scan is in some instances noiser has to do with collimation of the light before it passes thru the film. If you use a point source such as a laser or a single element LED, it will in fact be noiser. The Dolby LEDs both infra-red and Red are 2 x 12 arrays in order to reduce the collimation effect. Picture a single ray of light intersecting with a chunk of dirt on a soundtrack. The resulting shadow on the pickup is quite significant. If light approaches the soundtrack from a wider angle the effect of the chunk or speck is reduced as some or most of the light goes around the speck. Faster f2.0 lenses like the ones used in the latest reverse scan readers also improve noise performance over the first generation f 4.5 lenses for the same reason, ie, receiving light from a wider angle.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 08-17-2003 08:42 AM                        Welcome Sam! You are absolutely correct about the specularity of the illumination and collection having a significant effect on the "visibility" of surface defects. Diffuse illumination and collection are much less sensitive to dirt and scratches. The very diffuse illumination system in the Thomson Spirit DataCine (designed and built by Kodak) allows almost defect-free transfers without having to use a wet gate. Some of the earliest uses of "Wet Gate" were in sound readers.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 08-17-2003 11:20 AM                     Welcome Sam what took you so long getting here  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-17-2003 12:25 PM                       Would you beleive it's a simple as hating to do the paperwork to get registerd? I'm glad someone picked out a good picture of me as I had not chosen one. I probably won't be an everyday participant as I don't wish to appear too self serving on the subject of red or reverse scan readers, and despite some people's opinion of me, I don't know everything and don't wish to take the position that I do. As a good friend of mine at Dolby Labs if fond of saying, "Those of you who think you know everything are annoying those of us that do".  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 08-17-2003 01:00 PM                       Well, hello there, Sam! Hope you are doing well. Yes, you are absolutely right, thanks for clearing that up. I have no experience with the newer f/2.0 optics, as I've been out of the business for some time now. The last one I heard an old print on several years ago sounded just like the R4s! And, hey, we used to have the same saying around my old job! Haha. John P. said: quote: The very diffuse illumination system in the Thomson Spirit DataCine (designed and built by Kodak) allows almost defect-free transfers without having to use a wet gate. I wouldn't know, John. I could never get CineSite to give me a quote. Guess they figured us small potatos aren't worth the trouble.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 08-17-2003 01:05 PM                     I used to have a boss that would walk in and pick up a pencil off the desk and say "Hm this can't be mine the earser has been used"  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 08-17-2003 09:25 PM                        Yah, I bet that was a HUGE laugh-riot after about the tenth freakin time! And Jeff, congratulations -- you were able to make a $300 JAXlite (sometimes refered to as a JACKthisLite) for ten bucks! For a home theatre where you probably won't get to see cyan tracks for a long, long time, and then only on occasion, seems your solution is perfect -- you can switch exciters from white to red simply by pulling out one assembly and popping in another. Very well done indeed! Can you come work in my theatre? Now if only SOMEONE would make a reverse scan exciter array with dual LEDs -- red and white -- so that with a flip of a switch, those of us who run 99% silver tracks (and will be doing so long after I retire) can have the benefits of reverse scan, but can flip a switch to get red excitation for the occasional cyans. If only. Frank PS -- are we still going to call the light source, even if it is red, the exciter LEDs? Is the solar cell the scanner in the reverse scan unit? Just wondering.  |  IP: Logged Warren Smyth Expert Film Handler Posts: 158 From: Auckland ,New Zealand Registered: Aug 2003 posted 08-18-2003 05:27 PM                     Thank you Jeff for an inovative solution. I've been pondering the problem of a home brew for some time. I really want to retain the use of the conventional exciter for silver tracks and at the same time play cyan. I considered cranking up the voltage of the presently under run 9 volt lamp and placing a red filter in front but your's is a much more efficient method. Simply swapping the red light assembly for a exciter lamp doesn't seem too onerous. Can you tell me if there is much loss in output from the dolby cell with your conversion. I'm wondering if the gain adjustment on the preamp card of my CP50 will cope, or if an extra preamp stage is required to achieve correct dolby level. Lastly, how can I get one of these devices? Do you think the maufacturers will supply by mail to the public? There is always a demand for budget solutions. Thanks again.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 08-18-2003 10:34 PM                        The Thomson Spirit DataCines are used by many more tranfer houses than just Kodak CineSite. Kodak designed and built the illumination and scanning system for all of them however: http://www.kodak.com/US/en/motion/products/v2/sehlin04.shtml BTW, Kodak also provided some of the first high resolution scanning technology used by Industrial Light and Magic (Lucasfilm) over a decade ago.  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-19-2003 02:52 PM                     Warren, If you put a red filter in front of a white incandescent light source, you are left with precious litle red energy. The LED emits monochromatic (one frequency) red light so all it's output is useable. My solar cell output goes to just an analog preamp. I ran standard silver sountracks with this new LED source (don't have any cyan film) and it didn't require any increase in preamp gain from what I was using with a standard tungsten exciter lamp. There's a guy in South Bend Indiana that sells the Red Star LED's for $10 a pop, but I'm out of town now and don't have his phone number. Send me an email later in week and I'll get his info for you.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-19-2003 07:24 PM                     Filtering white light has two problems...First off, the solar cell is infrared sensitive, not red sensitive. So just putting a red filter in front of your exciterlamp will not filter out the infrared light...as such, with cyan you will have all that noise coming through as if it was translucent. Therefore, you need both a red and an infrared filter to make it a bandpass filter. Next comes fading...your filters are apt to fade over time so even if you got the wavelength right, it is apt to be wrong over time. Steve  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-19-2003 08:21 PM                       Regarding the LED replacing an exciter lamp. All off the shelf LED's are to my knowledge spot sources and will inevitably be brighter in the middle and fade dramatically toward the edge. A diffuser can be used to flatten out the light but the output will drop a bunch leaving you having to turn up the LED to get back to where you were before. Dolby Labs and USL experimented with off the shelf LEDs but both concluded an array was needed. The Dolby LEDs as well as the JaxLight are custom parts and the price is high due to the small volume used in this industry compared to the scale consumer LEDs are used in. What you are striving for on an analog track is even illumination. Typical slit lenses fade toward the outside edges of the soundtrack by about 3dB even with a perfect exciter bulb. Dolby Cat. No. 566 used in conjuction with an RTA is the reference to measure the uniformity of the light. Using a spot source behind the slit lens is akin to using a vertical exciter filament on a horizontal slit. (This was done without much success in the 50's in a misguided attempt to deal with the filament sagging). Light will get through but mostly in the middle. OK for speech but not for effects which are modulated out to the edge.  |  IP: Logged

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