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This topic comprises 3 pages: 1 2 3
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Author
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Topic: 3D spinning disk
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 02-07-2009 05:26 PM
I vote for a dual-projection passive Infitec (Dolby) system as the "best quality" solution, but pbbly too expensive to be practical and not w/o problems (i.e. colometry, gain screen).
I see 1 projector Dolby basically tied with Master Image as a "practical solution". They both "flash". Dolby loses more light and needs colour correction. Master Image (or RealD, for that matter) adds filters in front of the optical path (instead of Dolby which does it at the light source) and needs a silver screen (although the material from Dalite is almost no-gain and lacks silver weird-saturated images).
But Master Image (or RealD) suffer from (much) more ghosting than Dolby. Also, glasses for Master Image (or RealD) are basically give-aways and not the (holy) $$$$ of Dolby.
I would pbbly recommend a dual-projection passive linear polarized system on a special (non silver) screen formulation for best image with low cost. Virtually nothing for the filters or the glasses and only having an extra projector, which is not all that costly as they can be two small-ish projectors with reasonable lamps rather than a big-bright one on the biggest bulbs.
If you subtract the cost of Dolby (or RealD or Master Image) plus the 6kw lamps + big-ass projectors ... the economics of two "4kw projectors" (2x4kw=8kw) plus $200 for filters (and very cheap glasses) is not too bad. Sure running/maintaining 2 projectors/bulbs is not cheap, but we are talking the "best quality" (reasonable) option, not the cheapest one. But owning two projectors can also have its advantages. I.e. if 3D completely dissapears for whatever reason, you are not left with a "worthless" expensive filter wheel by Dolby. You could just sell the second "extra" projector or use it in another screen or as a spare.
Reasonable (7-8fl) light levels can be obtained which would be hard with a single projector. Remember in dual-projetion an additional 7% of the light is not lost due to blanking interval plus the filters can be much brighter than a Z-screen or a circular one, while having significant (75%) less ghosting at the same time. So, generally speaking (i.e. not exactly, but you get the point), two 4kw projectors would yield the brightness, compared to RealD, of about 4kw+4kw+7%+5%=9kw while having 75% less ghosting (but the audience must be advised to keep their heads straight ... alternatively you could use circular polarization to avoid that and lose about 3% of the light plus obtain perhaps only 5% less ghosting than RealD z-screen, instead of 75%).
The screen itself pbbly has to be changed anyway for any of the systems, be silver/special for Master Image/ReadD/Dual polarized or high-gain white for Dolby/Dual-Infitec.
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 02-07-2009 07:24 PM
quote: Mark Gulbrandsen
Show me decent CP filters large enough to properly dissipate heat that cost only $200.00... they don't exist... try more like $1200.00 a filter for 11X14 inch AR Glass size which is the minimum size the CP filter manunfacturer we used reccomended for 4kw D-Cinema and up.
Here there is a linear plastic 8.5" x 15" for $37 retail
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1912
You can laminate it in glass if you want. If you want them circular, just add a $10 retarder film.
If you want to buy them already made glass circular, I've seen them in 8x8 for $120, don't quite remember where. Here is a place with all kinds, including a 6x6 inches circular glass PAIR for $465. This is for a PAIR of them, circular, glass, and for use in projection.
http://www.berezin.com/3d/filterholder.htm
First one I found with google. FAR LESS if you go straight to a polarizer manufacturer. I used to purchase full sheets (something like 4 by 2 feet) from Polaroid for like $100.
Here are acrylic, circular, 11"x15" for around $150. They also do glass, if you want, but acrylic is just as good for this use, as it's being used in the Master Image you love so much. This is full retail.
http://www.apioptics.com/circular-polarizers-spec.html
Here is a glass, AR, circular polarizer, aprox. 11"x15", 3M manufactured one for $182. Made for high resolution monitors, so it must be good optical quality. Basically satisfies your requirements, although not for the intended use, but shows it can be (easily) sold retail at those price levels.
http://www.officemax.com/omax/catalog/sku.jsp?skuId=20367381&cm_mmc=GBa se-_-Technology-_-Computer_Accessories-_-Glare_Screens_Privacy_Filters&ci_src=14110944&ci_sku=20367381
Remember in the 80's a small piece of polarizer in front of mirror boxes, prismatic adapters or even in front of split lenses (i.e. less than 3x3 inches) was taking all the heat from the (say around 3K, dual-blade shuttered) projection lamps.
Sure they suffered, but replacing them every couple of years was a good quality assurance method and at $50 or so for a pair of small linear, a good choice.
For 4KW digital, I'd say use anything glassed over 6"x8" and just change them regardless of usage every so many years. $200 each could do just fine if you know where to find them or purchase quantity from manufacturer. I just meant my $200 figure as a generic thing, plus I was referring to linear (thus the 75% improvement in extintion ratio). But you could go anywhere from $10 for a small piece of plastic linear to $1000 for a large piece of glass circular, of course.
11x14 is overkill for 4kw, but good if you want them to last for 100 years ![[Wink]](wink.gif) Not even RealD's zscreen is that large size, it's more delicate, retains more light (heats) than a passive filter and it's used with projectors up to 7Kw all over the country ... not even Imax 15kw used filters that big of a size ...
http://www.youtube.com/watch?v=AKr7yS9Rx6I
... still, I could do circular, glass, 11x14 for $200 easy. It's just not your average standard product that I can point to a web site with a price on it. I would have to custom make it (my cost pbbly $30-$125, depending on materials used) or custom order it to have it made for me (pbbly at quotes of less than $350 each if I order a pair).
But to be honest, this is not entirely true. Depending on the manufacturing process used in the polarizer, this would either quickly degrade with time if light is shined through it (noticeable in just a few years, useless, less than 60% as effective in as little as 3 years), or almost not at all, even if subjected to large luminous flux . Projection zscreens are made with a wire grid polarizer, so they are not anywhere nearly as delicate as those made with organic materials, iodine or dyes and can survive easily huge fluxes in small(ish) sizes.
My advice: just get a reasonable (say start at 6x8, go up to 10x12) inexpensive filter and replace it "often". Also, circular retains more light than linear due to the two optical surfaces, so it needs a bit larger area to "suffer" the same as linear. About 4-8% more, depending on manufacturing process used.
Or use a wire grid polarizer and you can have a small size and still have it last "forever". Add a retarder if you want it circular (retarders absorv very very little light ... any reasonalbe size, even the size of the lens, would cope with the flux w/o problems after the polarizer).
And at $1200 for a 11"x14" circular filter it's way too expensive ... for that price you could almost purchase a whole zscreen 13"x17" ACTIVE ZSCREEN, which includes a high quality glass circular polarizer that "alternates right and left" to cover a 21" diagonal high resolution monitor, including two pairs of quality fashion circular glasses, power supply, monitor interface, etc .... at full retail ...
http://reald-corporate.com/scientific/zscreen.asp
Honestly, a zscreen can be manufactured for PEANUTS and polarizers, specially linear, for peanut's shells. But as I've said before, manufacturing COST and selling prices are entirely different things.
I would be very surprised if the filters in the Dolby wheel don't degrade with time in the highest lamped models (where they'll be mostly used). It will depend on the manufacturing materials used, so it is NOT necessary for them to degrade, but somehow I feel they didn't go the exotic materials route.
I would also feel that the Master Image filter would degrade, but not nearly as much. They probably made the right choice of use inexpensive iodine filters and just have the wheel changed every so often. My totally wild guess: every 2-4 years of daily use on high power projectors. Since 3D movies are not a daily thing yet and not all projectors are 6Kw ... pbbly less often.
How much is the retail for the Master wheel, Mark?
For once, the Dolby baby receives the raw light and heat, absorbs around 73% of it, doesn't benefit from the 7% "black period", lives inside the "heat case". RealD-zscreen/Master-disc receive the light after it's gone through the whole optical system and lens, retains only about 58% of the (remaining) light, benefits for a 7% dark period rest, and spreads the flux over a larger lighted area while cooler outside in the booth or rotating like the Master.
[EDITED to add more websites were similar products can be bought at those price levels plus add more rant ... please, re-read the whole thing ]
[ 02-07-2009, 10:23 PM: Message edited by: Julio Roberto ]
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 02-07-2009 10:40 PM
quote:
Sorry but you can't make filters that are polished to quarter wave, have AR on them and just 4mm total thickness unless you have similar factory conditions. The reason for largish filters is to spread the heat over a large area so the filters have a very long life, the glass also helps greatly to not only filter the remaining UV and IR light but also absorbs the heat before the plastic filters do.
I can source 1/8 wave AR optical glass and laminate thin films on them with necessary precission with the result of slightly over 4mm total thickness for circular if I needed to. Easier to let a polarizer manufacturer do it (as you did with Colorlink), since it's their bread-and-butter and setting up for it is not worth it unless I make a couple hundreds run.
I agree and recommend glass for the reasons you mention (additional light loss, but greater UV and IR rejection and heat spreading/absortion of additional mass, plus durability and easy cleaning), but such large size is not necessary for 4Kw, but it never hurts to go over-specs than under-specs.
We've already gone thru RealD being circular or not. All retarded polarization is elliptical, with circular being one of the cases for it. The only difference is how you align the retarder and the polarizer. You align fast/slow axis perfectly perpendicular with the polarizer and you get perfect circular. You rotate the retarder a bit ... you get elliptical ... a bit more ... more elliptical ... a bit more ... until you are back to were you started ![[Smile]](smile.gif)
It just means that RealD decided, for whatever technical or marketing reasons, not to align the active retarder and the polarizer to 90º, but 45º or another in-between angle. So the only problem is that the manufacturer of the glasses (colorlink) for RealD compatible systems would have to rotate the retarder to the correct angle to make the CP filter work with their Zscreen.
[ 02-07-2009, 11:44 PM: Message edited by: Julio Roberto ]
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 02-08-2009 12:42 AM
Regular standard Circular polarized paper glasses can be bought in the open market for less than $0.40 each in small quantities. I hope Master Image made the polarizing filters standard circular.
Alternatively, you can buy "theme park style" or "dolby style" reuseable plastic circular polarizing glasses for less than $4 in small quantities. You could collect them, wash them, and re-use them. If they get stolen or lost or broken, not too big of a deal ... certainly not as bad as with Dolby or Xpand
If you commision a huge run from a chinese manufacturer, certainly less than half, even 1/4th, of those prices quoted.
For those that would use a dual-projection linear polarized system, the advantages with respect to circular would be:
-Better extintion, less ghosting. About 75% improvement.
-Better transmission, more light. About 4% improvement.
-Lower filter projection costs. $200 should easily do it.
-Lower glasses cost (i.e. 30-50% less than quoted above).
Main dissadvantage: cost of two projectors (but they could be two smaller models, as the light output is more than "doubled") and the audience needs to keep their heads aligned with the screen. Those sitting too far in the corners of a wide theater or those tilting their heads towards their shoulders would quickly start seeing a lot of ghosting.
For those that think that linear is "not acceptable", please remember that most Imax 3D theaters have always been linear, same as 3D in the 50's and the 80's and all current multimillion attractions in theme parks. A little on-screen advertising reminding people not to tilt their heads is usually sufficient.
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Barry Martin
Expert Film Handler
Posts: 203
From: Newington, CT USA
Registered: Jul 2002
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posted 02-08-2009 01:40 AM
Mark, which tech were you working with and at which location did you install MI? Just curious, as I am currently employed with Bow Tie Cinemas in Hartford, CT and we had an MI 3D system put in a couple months ago. The tech I met was very friendly and was very open to answering all my questions, which were numerous. I am the first to admit I know next to nothing about digital projection as the last few theaters I worked in did not yet have digital, so his sharing time with me was most appreciated.
They did have to make a trip out to replace the motor that raises/lowers the wheel. As he explained it, they were actually putting BACK the original motors because there was an issue with the "new and improved" motors burning out.
In regards to the quality of the 3D, I whole-heartedly agree this is the best system I have seen so far. I have not had the opportunity to see the Dolby setup, but I have watched a few features in ours and could not be happier with the setup, be it 2D or 3D. I had actually been a bit unhappy about us getting digital put in at first, just because I have preferred film for so long. But once I saw this running I was hooked.
As far as the raising/lowering of the spinner goes, we did not have an issue when running Bolt as there are plenty of trailers for 3D kids movies coming out. When Bloody Valentine came out the only trailer that was supposed to be placed and was in 3D was Coraline. As it is we do not run any ads (a Bow Tie thing), so there is typically only 5-10 minutes of previews and then the feature starts. Considering most people are used to having 15-20 minutes of extra time to be late to a movie, running only Coraline for previews and starting the feature 3 minutes after showtime was a bit of a problem.
So we setup the playlist on the Doremi to start a 2D show, play the 2D trailers we had been directed to play, then set in a "black" pattern and set the cue to start the 3D show with Coraline's trailer and the feature.
This works pretty well, and has a strange little side-effect of making the 2D trailers seem to stick out a little from the screen. I would prefer to have a track system as you mentioned, but this is a 17 screen with one person running the booth at all times so I doubt that could happen.
The one thing I am trying to work out (without having to use my technician if possible) is hooking a Blu-Ray into the digital projector/sound system. We have had occasions in the past where a local festival or school wants to rent an auditorium and then had to bring their own digital projector running off a laptop since they had no 35mm copy. The projector itself is not much of an issue as there is a DVI input, but I cannot for the life of me figure out where I could get a cable that goes from the digital coaxial or optical to the I/O on the processor. I certainly don't want to use the RCA left/right I have for the non-sync and just do stereo. Eventually we are planning on using this house as a DVD screening room for off-peak hours. Any idea where I can find what I'm looking for?
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