This is topic Has your screen brightness improved with digital conversion? in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.


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Posted by David Kilderry (Member # 142) on 09-17-2011, 12:22 AM:
 
I have noticed some local theatres here have a vastly improved brightness since their digital conversion (close to correct now). Others, in my view, seem dim even on 2D compared to when they were 35mm.

As a drive-in operator, I'd certainly be looking for an improved light output from the big Barco 32B (or equivalent Christie CP2230 or NEC) compared to our current 5,000 watt Strong Xenon lamphouses.

Has your theatre improved its light with the digital conversion? What can we expect at the drive-in? Our three largest screens are 80 feet wide on scope, 5,000 watt xenons, projectors are Phillips DP 70 and Century DAW 2.
 

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Posted by Monte L Fullmer (Member # 2797) on 09-17-2011, 02:20 AM:
 
I was running 3k lamps in our Christie SLC consoles in houses that were previously running 35. Now, with BARCO 20C units with a 4k bulb in it, the brightness definitely has increased.

To make things simple for to see if your screen can reflect a good image is to measure and record down the length of throw from lens to the left corner of the screen and the width of the screen itself.

These two measurements will be needed to begin to see if a
31000-lumen 4K Digital Cinema Projector
Model: NC3240S can light up the screen. This unit uses a 6k bulb.

Contact your dealer for help on this one and give these two measurements above to your dealer so a project can be started.

-Monte
 

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Posted by Dave Macaulay (Member # 813) on 09-17-2011, 10:00 AM:
 
This is a fairly meaningless question.
Maintenance on 35mm projectors has been dismal for years (there are exceptions, but the big chains have adopted a "fix it when it breaks" maintenance plan. That may be because of the impending digital takeover - why spend $$$ maintaining a machine son to go to a scrapyard? Even when regular maintenance actually happened, a mirror had to be really really bad to warrant replacement.
Then there's the economics of conversion. You have to pick the projector that will light your screen adequately. Usually you have at least two choices, one that just does it and one that can go well over yoyr target. The smaller one is always cheaper, but if you just look at total lumens and push the limit you'll be in trouble. lamp output drops a lot as it ages and your new silver screen will get dirty from crap in the air.
After a new conversion, especially if you put in a new screen as well as the projection system, the screen brightness should be better that with the tired 35mm lamphouse mirror and high-hours lamp it replaced.
If you spec'd a digital projector with adequate headroom this better light level will be maintained for a long time. If you are just making the target at 100% lamp power with a brand new system the light will drop as each lamp ages and as the mirrors and screen degrade.
For conversions not part of a VPF plan, maintenance continues to be optional. We'll see if the owners keep their new projectors properly maintained. What I've seen so far is not encouraging. Warnings don't help: I came across a Christie that had flashed its big red "lamp life exceeded" warning for 2000 hours of lamp life without any action from the management or "projectionist". Filters clogged beyond belief are not unusual to find. Coolant tanks with a few drops remaining aren't unusual either.
What I notice more than absolute screen brightness is the flat light a digital projector gives. With a matte screen there's none of the hotspot or corner dropoff that is endemic with film systems. The light pipe integrator scrambles the incoming light to pretty much give equal illumination corner-to-corner. You really have to misalign the lamp badly to get a brightness gradient across the image. Too bad nobody could come up with an affordable integrator a system to light a film frame.
 

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Posted by Louis Bornwasser (Member # 3063) on 09-17-2011, 11:00 AM:
 
In the Louisville area, film averaged 20+ ft/lamberts.

Now, with digital, it is about 8 or 9. It is hard to find a cinema that is good enough to go to. Louis
 

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Posted by Steve Guttag (Member # 268) on 09-17-2011, 11:25 AM:
 
Here is the bottom line...if you sucked as a film operator...you'll continue to suck as a digital operator. The "you" here not being anyone specific but an entity that runs theatres.

Dave is partially correct on the quality of light improvement. I say partially because he is right that digital will often have a superior uniformity but not because of any intrinsic issue with film projection. With most diigtals, much of the critical alignment is taken away from the installation technician and put in the hands of the factory. Furthermore, the optical path itself is no longer a "Frankenstein" of what the exhibitor "got a good deal on" but rather few choices are offered. That is, the reflector, light pipe, DMD portion is already chosen for them once they pick a projector...this pretty much leave the lens...which often has few choices in a given size. The lens was designed for the specific imager (DLP or DILA) and has to be approved by TI/Sony. Now there is plenty of room for non-uniform illumination (and I'm finding that they are not as perfect as one would be lead to believe). One also does not have the ability to "tighten the focus" to brighten up the center of the image (which also typically will degrade resolution...there is but ONE sweet spot for a arc lamp/reflector combination that will put out a perfect cone of light). Getting a uniform field of light with film is not that hard though it seems to elude many folks.

Monte...where the eff do you get this measure from lens to left corner nonsense for the throw? If you don't really know something, don't spew bad information.

Calculating light for digital is somewhat easier than for film. With film, one has to consider, as mentioned above, a great many undocumented things. Lamphouse efficiency, shutter efficiency, lens efficiency as well as the interaction of the lamphouse optics to the lens via the projection gate. Most shutters have a nominal 50% efficiency (give or take 5%). With the exception of the Kinoton E Premiere line that is about 20% better than that...but we'll consider those rare in typical cinemas.

But looking at this situation...the screen tower is approximately 33.5' tall and 80-feet wide.

Drive-ins get a benefit from digital because of their long throws. The long focal lengths of drive-ins typically require either 4" diameter lenses or suffer from slower lenses due to the maximum diameter of the typical lens 70mm. Scope gets hit hardest as Reverse anamorphics are often used. So in film, they often suffer in light there...with digital...the lenses do not have such small elements that they affect the longer EFs.

Lets say your screen has an effective gain of 1.0...in theory, you'd need a 15KW lamp to get that thing up to 16fL using modern lenses that are very light efficient and that you are not using anything over 140mm in EF. If you gain is higher, the lamp requirement would be relaxed a bit...but as I have stated elsewhere...when gain in the screen is used...one does NOT get to merely keep the same 16fL (film) or 14fL (digital) center spec...that was based on you light also being at least 85% on the sides as the center. Any screen gain above 1.3 will never achieve that though Drive Ins again have an advantage here...their projection is so long, the angle of attack of the light does not reflect off to the sides like it would in a hardtop.

Lets say your gain is such that it is nominally 2.0 (it doesn't really matter for this example...so long as we are uniform about it). That drops your lamp requirement down to about 7300-watts. That would put your light at about 11fL on a perfectly clear day and the screen at 2.0 gain...if your screen gain is less...closer to 1.0...then your light is going to be down closer to 5-5.5fL Again, longer EF lenses will also start to factor in here to knock it down a bit further.

Now lets look at digital...

To light that screen up with digital to hit 14fL and be able to sustain that (allow about 25% for aging)...you will need 34244 lumens. The Barco you cited running a 6.5KW lamp will hit 33,000 lumens with a new lamp running at max with their most efficient lens. However, since I've built the 25% into the lamp requirement...it means you could run at about 13.5fL and sustain that...IF you happen to have the most efficient lens and have it zoomed to its most efficient position (maximum image). The realities are, you are going to get somewhat less but still more than film! But remember, you are running 30% more lamp in there to do that and the lamp has been specifically designed for the lamphouse to be more efficient (digital lamps are almost always about a bulb size better than their film counterparts).

Now, if you equip your projector with an anamorphic lens...you can get another 23% boost in your scope image brightness. Your lumen requirement drops to 28000 lumens...this would let you hit spec for the life of the lamp and burn less electricity too.

Conversely, if your gain is closer to 1.0...then your digital light will be closer to 6.5-7 fL without the anamorphic or 8fL with it. I'm speaking of "SCOPE" light...flat, with digital will be notably brighter that scope without an anamorphic.

-Steve
 

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Posted by Victor Liorentas (Member # 5272) on 09-17-2011, 11:37 AM:
 
I may have had bad luck but in the few times I have gone to a digital cinema it has been a shock!One screening I watched had a broken integrater rod which produced a dark soft picture,the last show I saw in a new install was just bright enough but out of focus!?
The port glass is always filthy so contrast is bad every time.I mean angled port glass collects dust fast and it seems to be more neglected than it used to be when film was being used and an operator might clean it from time to time.
I have seen small screens pop with a sharp bright image but only during the first month of operation. A dusty window and dirty Z screen take the perfect out of digital projection faster than a film break!
 

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Posted by Monte L Fullmer (Member # 2797) on 09-17-2011, 03:33 PM:
 
Sorry once again, Steve - what I was told. Then, what would be the correct procedure to set the record straight?
 

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Posted by Steve Guttag (Member # 268) on 09-17-2011, 08:17 PM:
 
Yes...throw is straight. and the distance is from the effective focal plane to the screen...the projector manufacturer is suppose to indicate that somewhere. It is close enough to use the front of the projector but it will likely be a few inches behind that.

-Steve
 

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Posted by Mike Blakesley (Member # 26) on 09-17-2011, 08:49 PM:
 
In 35mm days, we had a 2000w bulb in a Christie lamphouse. The system always had yearly tune-ups along with periodic maintenance by me, so it was pretty much optimal. I always thought the picture should have been brighter and wished we'd gone with a 3000w bulb back in the day. We have a 30ft screen and a 95' throw.

With the digital, we went with a 4000w bulb, mainly to make 3D be brighter. It is a noticeable difference on the screen.

It's hard to see the bulb getting darker with age since it's so gradual. But I was surprised at the difference when we replaced our bulb a couple of weeks ago. We changed bulb brands too so that might have been part of the difference.
 

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Posted by Monte L Fullmer (Member # 2797) on 09-17-2011, 09:31 PM:
 

quote: Mike Blakesley

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We have a 30ft screen and a 95' throw.

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