Film-Tech Forum ARCHIVE: Laser light source for 35mm projector?

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Posted by Phillip Grace (Member # 2262) on 08-27-2019, 08:44 PM:

Hi All.
I've recently come into contact with a couple of laser digital projectors, one Christie and one NEC, and standout features are that they are both quiet in operation and appear to be economical because they dont consume Xenon bulbs. The relatively short life of high current xenons in digital projectors is a concern.
Would it be possible to apply the same light source to 35mm film projectors, and gain those advantages, along with cooler light, and a more even field?
I'm assuming that the light engines in laser digital projectors still split white light into RGB and recombine it for projection in the same way as xenon light-sourced digital projectors, and that somewhere in the light path there would be a white light field approximately the same size as a 35mm film frame, such as the end of an integrator rod.
I'm imagining a newly designed lamphouse as a total replacement for a Xenon unit.
Any thoughts?

Posted by Steve Guttag (Member # 268) on 08-28-2019, 02:49 AM:

Nobody is going to develop a laser light source for film, at this point. The market is WAY too small. Those theatres still running film get something like 10-years on a lamp because of how little use they have.

In 2019, it is still cheaper to run disposable xenon lamps in digital projectors for anything under 3000-watts...about on par at 3000 watts and cheaper for laser above.

Lasers are inherently NOT white light. RGB lasers, in particular, as the name implies has the three primary colors.

The laser-phosphor projectors typically start with blue (two blue lasers comprises of several banks) and filter one of them into yellow to attain the spectrum. Higher-end laser-phosphors use Blue and Red lasers with an extra blue with a green phosphor wheel to get the third color.

You've now introduced an electromechanical wear part (the phosphor wheel) which makes the system yet more expensive. Furthermore, color wise xenon will best any of the Laser-Phosphor systems for color spectrum.

Which brings us back to...nobody is going to make a laser-based light source, at this time for film (to do commercial projection...perhaps some sort of small-scale thing). Now, as laser based light continues to become cheaper, this may change. Barco's SP4K series in quite intriguing as they have gotten RGB laser 4K to be on par with the pricing of Xenon 4K but without the cost of xenon lamps and at a lower electric cost. Perhaps, down the road, that sort of technology could be retrofitted behind a film projector but it isn't exactly simple but who knows what the future holds. Film projection will remain a very tiny market

Posted by Phillip Grace (Member # 2262) on 08-28-2019, 08:52 AM:

Hi Steve. Are you saying that the bandwidth of the individual Red Green and Blue laser sources is too narrow to create a full spectrum white light field when they are added together?
I guess that makes sense, having now read that certain RGB laser source dual projector systems for 3-D have 6 laser sources with 6 specific bandwidths with appropriate colour shift for left eye and right eye.
Cheers.

Posted by Leo Enticknap (Member # 534) on 08-28-2019, 09:28 AM:

The problem I anticipate goes beyond simple economics. Agreed that at present and for digital projection, xenon still makes sense in many situations. However, the new generation of RGB laser projectors, e.g. the Barco SP4K and Christie's competitor, is, IMHO, likely to hasten the retirement of bulb projectors in many cookie cutter-type multiplex screens. That's not just because it does away with the need to buy $1k bulbs every few weeks, but also because operating costs are being reduced in other ways - longer laser cluster lifetimes (claimed, at any rate), less planned maintenance required, and lower power consumption being other developments.

Unless, as with electric car batteries, we get to a sticking point with laser (digital) projectors at which the price/performance deal simply can't be improved much further, the natural cycle of equipment reaching EOL and being replaced will steadily reduce the number of xenon bulb projectors operating in the field. The end result will be manufacturers reducing their ranges, increasing prices, and then ceasing production altogether.

I'm not going to be as bold as to predict when this will happen, but - and sorry if this sounds smug - I do remember predicting about 6-7 years ago that if and when film projection eventually becomes impossible, it won't be because it becomes impossible to maintain the projectors themselves, but either because release print stock and processing goes away (still a possibility, given that there is now only one manufacturer of dye-coupler color release print stock and its processing chemistry left in the world), or because no-one makes xenon arc bulbs any more, and the R & D needed to create an alternative light source for film projectors proves to be an insurmountable economic barrier, given the size of the market.

I have seen 8mm and 16mm projectors retrofitted with LED illumination, and the projected image looks very impressive. However, my understanding is that there are significant barriers (mainly to do with heat) to scaling that up to create a big enough light source for a 35mm theatrical projector.

Posted by Marcel Birgelen (Member # 6801) on 08-29-2019, 01:17 AM:

I've experimented with a LED source for a 35mm projector once, but the results were less than stellar. It's pretty hard to combine multiple LED arrays into a point source and although the LEDs should be at the "right" color temperature, the colors looked distinctly off, compared to a xenon light source. The spectrum of colors produced by LEDs is vastly different than that of xenon.

One of the interesting features though, of light sources like RGB laser and LED is that you could potentially get rid of the mechanical shutter, instead of the shutter blocking the light during film transport, you simply switch the light source on and off.

Posted by Steve Guttag (Member # 268) on 08-29-2019, 06:13 AM:

Just before Kinoton GmBH exited the film business, they brought out their Film Viewing Table (flat bed like device) and it indeed used a strobing LED system to light the image. It was actually a pretty cool device that could run most any film, regardless of how shrunk it was.

Posted by Mark Gulbrandsen (Member # 72) on 08-29-2019, 08:50 AM:

Inexpensive LED light engines are here now. Something like this scaled up to a couple hundred watts would work. There may already be much larger light sources than this one available.

LED Light Engine

Posted by Leo Enticknap (Member # 534) on 08-29-2019, 09:33 AM:

quote: Marcel Birgelen
One of the interesting features though, of light sources like RGB laser and LED is that you could potentially get rid of the mechanical shutter, instead of the shutter blocking the light during film transport, you simply switch the light source on and off.

That method has been used in the telecine and film scanning world since the early '00s, starting with the MWA FlashScan. The archive I was working for at the time bought one of the first (standard def PAL) models, and when I went to their factory in Berlin for the training (in, I would guess, 2003 or '04), I remember thinking that the thing was science fiction, and wondering how long it would be before LEDs were powerful enough to use the same film transport mechanism for a projector. Continuous motion, so very kind to film, and the following generation of models were sprocketless, with the film moved by a combination of friction rollers and being pulled through the mechanism by the take-up motor (same as in a reel-to-reel tape recorder, but with a lot less pressure than the pinch roller applies), so no problem with shrunken elements.

There are now at least six or seven manufacturers that make continuous motion, flashing LED scanners, but MWA was the first.

Going back even further, Steenbeck developed a totally analog approach to continuous motion for their viewing and editing tables, using a rotating prism. But with both the rotating prism and flashing LED methods of replacing a mechanical intermittent, the problem was always scaling up the light source so that it was powerful enough, and of a good and stable enough color temperature for projection. If and when xenon bulb manufacturing goes away, I anticipate that the LED lamphouse for conventional projector option will be explored further, but, given the size of the market, R & D costs could be a major obstacle.

Posted by Frank Angel (Member # 248) on 08-29-2019, 02:30 PM:

quote: Leo Enticknap
I have seen 8mm and 16mm projectors retrofitted with LED illumination, and the projected image looks very impressive.

Leo, I'd be very interested in any information you could give on LEDs that you saw working decently for 16mm. We have been trying to achieve decent light levels without the heat of halogen or incandescent.

Posted by Scott Norwood (Member # 30) on 08-30-2019, 09:34 PM:

I just want a 35mm xenon lamphouse with an integrating rod, like the design used in the DLP lamphouses. That would seem to be totally do-able, unless I am missing something, which I might be.

Posted by Steve Kraus (Member # 476) on 09-01-2019, 10:02 AM:

Isn't the actual laser diode just a tiny dot with a cluster of them being the light source. I think it was Barco that was showing how their light source units were individually replaceable units that you could hold in the palm of your hand.

For digital, you'd want the three colors separate so they can illuminate three DMDs and then combine.

But for film there would be nothing wrong with a white source, that is, a unit combining laser diodes of all three colors, interspersed.

So if Barco has three palm size units to provide theatrical-level illumination, be able to be cooled, and have good life, how about a single panel of roughly 3 times the area upon which are placed interleaved R G B laser diodes? From there you have condenser optics to properly illuminate an aperture. MAYBE you include an integrator rod in the system but not if you can keep the dots so well diffused and out of focus that it's not necessary.

Posted by Phillip Grace (Member # 2262) on 09-01-2019, 09:28 PM:

I'm not particularly concerned about the commercial aspects of system development.
More interesting is whether the laser illumination is technically applicable to film projection and how close the current technology is to achieving it.
Although film projection has all but vanished from mainstream exhibition there is an ongoing interest in various cultural institutions, film archives and libraries etc. for the experience. This kind of institution is usually well enough funded to embark on any project of sufficient merit. Economies of scale don't necessarily apply.
I think it is also fair to say that some existing films will never be available in digital format,and that long-term preservation on film will always be a heck of a lot more reliable than any method of digital "preservation". Much of our film heritage owes a lot to fortuitous and somewhat random survival. This will not happen with digital production. Worse than that though is that a selection process must be applied at the outset.

Laser illumination for film projection seems to offer certain desirable features for cinema projection. Cool. Quiet. Compact. Bright. Economical. Even distribution. Scalable. Available and serviceable into the future. Mainstream technology.
There is also the potential of adjustable colour balance, to compensate for variations in reflector colour temperature in dual projector installations, which has not been available since the days of the carbon arc. Global standardization of screen colour and luminance are easily achieved.
I would take that further, in that it might also be possible to balance the light output to match historic light sources such as limelight and low intensity carbon arcs, to recreate that viewing experience safely in a modern environment, and on a large screen to an assembled audience.

I think the main issue lies in the application of laser illumination technology to the subtractive filtering found in colour photographic film. This would seem to require a laser light source with a continuous spectrum.
Can it actually be done?

Posted by Mark Gulbrandsen (Member # 72) on 09-02-2019, 08:36 PM:

Once a laser light source is assembled for film then it makes sense to add the integrator rod as Scott points out, into the scheme of things. It is certainly possible to assemble a light source as in the link I posted above. Cost on that entire assembly is only a couple hundred dollars for 20 watts of laser light. The question is, how many lumens is that 20 watts of laser light?

Mark

Posted by Carsten Kurz (Member # 5396) on 09-03-2019, 05:42 AM:

Why would someone keep up a specific technology like 35mm for historic reasons, only to get rid of a fundamental key aspect (carbon/xenon) strongly associated with that technology?

A continuous spectrum light source can not be a laser light source. You may use laser light sources to stimulate a white light source, as it is done in phosphor conversion projectors - but the light that comes out then is no longer laser light.

Also, just because it is a laser light source doesn't mean it is easy to create an even light distribution across a (comparably huge) 35mm film gate.

quote: Phillip Grace
Laser illumination for film projection seems to offer certain desirable features for cinema projection. Cool. Quiet. Compact. Bright. Economical. Even distribution. Scalable. Available and serviceable into the future. Mainstream technology.

Hmm. Aren't those exactly the reasons why everyone went digital?

- Carsten

Posted by Phillip Grace (Member # 2262) on 09-03-2019, 09:21 PM:

Carsten. I think you have missed the point. The object of the exercise is to keep film projection viable into the future, and to improve the technology involved where possible.
I think it unlikely that any authority would permit a carbon arc installation these days, apart from there being virtually nobody who knows how to operate one. Who makes Carbons now? Who will make Xenon short arc lamps 20 years from now?
The conversion of the exhibition industry to digital technology had nothing to do with the light source in the projectors - (which themselves may be supplanted by matrix screens). It was a commercial decision to adopt a technology which serves the interests of Distributors and Exhibitors far better than photographic film can in the current era.
There will continue to be an interest in screening film prints from archive collections for the sake of the viewing experience - in much the same way as there is an interest in seeing nitrate prints by direct projection now.
- Phillip.

Posted by Marcel Birgelen (Member # 6801) on 09-04-2019, 07:49 AM:

Personally, I don't see light sources as the biggest challenge to continue film presentation in the future.

There were millions of cars sold with xenon lights in them, they'll be around for a while in one form or another.

Laser right now is an up and coming technology for high-powered light sources, some deluxe car models are currently fitted with laser light, but it's still horrendously expensive. Costs for this will come down and if the supply of carbon arcs and xenons run dry, there will be other powerful light sources that can be adapted to take its place.

Nobody can give you any exact predictions about the market for light sources between now and 20 years in the future.

There is a bigger challenge in keeping film alive than light sources and that's the film stock itself. Once the demand drops below a certain level, it's no longer profitable for whatever remains of Kodak to make it, the supply is in great danger. Also, it's clear that making film stock requires a skill-set and machinery, not easily duplicated, otherwise, there would be multiple shops in Shenzen doing it...

Posted by Carl Martin (Member # 1146) on 09-07-2019, 03:48 AM:

quote: Phillip Grace
Who makes Carbons now?

marble company of japan. manufactured in indonesia and somewhat expensive to import. but they're decent quality.

they may still be manufactured in india as well but stay far away from those.

Posted by Carsten Kurz (Member # 5396) on 09-07-2019, 07:45 AM:

Many cinemas still have boxes of carbons stored, and you can still buy them frequently on ebay. Given that cinemas stopped using carbon in the seventies, we can still buy them now, nearly fifty years later. Not for a daily operation, but who does play carbon as a daily operation? So, for how long will there be Xenon bulbs available, given that they are still manufactured in high quantity today, and played/used as infrequently? There simply is no incentive to develop a laser light source for film. LED for special applications, yes, that is much easier to start with.

- Carsten

Posted by Carl Martin (Member # 1146) on 09-10-2019, 05:47 PM:

quote: Carsten Kurz
who does play carbon as a daily operation?

the stanford theater in palo alto, california, for one.

Posted by Marcel Birgelen (Member # 6801) on 09-10-2019, 07:33 PM:

I don't think that LED will scale for anything other than 8 or 16mm, without some serious R&D. For 35mm, you need some professional optics, which cost a lot of money to make, at least that was our conclusion after we tried this ourselves a few years back. Although LED intensities have only improved since then, I still think you won't escape to combine multiple light sources if you try to light up 35mm on anything other than a tiny screen. Combining multiple light sources and focusing them correctly isn't impossible, but it's more than just a Saturday afternoon hobby project, it will require some custom optics that need to be measured, calculated and produced.