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Author Topic: Contrast issues nec3240s
Fernando Caldeira
Film Handler

Posts: 41
From: Lisbon , Portugal
Registered: Mar 2010


 - posted 06-02-2018 06:56 AM      Profile for Fernando Caldeira   Author's Homepage   Email Fernando Caldeira   Send New Private Message       Edit/Delete Post 
Hi enveryone,

We've been having some complaints from local directors due to the lack of contrast on our projector.

I think we have done everything possible on the projector and last month we screen a movie called "DRVO - A ÁRVORE" which is very dark, and we couldn´t see half os the movie.

The room has egg shell coloured walls which I know its not very nice but it´s an old protected building that we can´t touch.

So now I´m trying to find out if chaging the screen could solve this problem.

The room seats 830 but as very high sealling, about 15m.
The screen is 16m wide by 5.5m high.
The Projection distance is 30m. ( I think this doesen´t help)

Should I get a silver screen? Will it ruin the 35mm projection?

We don´t do 3D anymore.

The room:
 -

A smple of he prblematic film:
 -

Thanks in advanced for any advice.

Cheers
Fernando

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Dave Macaulay
Film God

Posts: 2133
From: Toronto, Canada
Registered: Apr 2001


 - posted 06-02-2018 10:54 AM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
I don't know if you can fix this, it looks like a director/cinematographer problem more than a projector problem. Like they timed it on a TV and expect it to look good in a cinema.
Standard 4K DMD projectors do not have excellent contrast. But timing a print to be in the bottom 10% of the luminance is not a good choice.
The light walls are a problem, and you are stuck with that. A gain screen will cut down the problem a bit. The gain screen hotspot will affect any projection equally, film or video. A high gain screen would be pretty bad, a mid gain one should be acceptable.
I doubt if that movie would look too good in any cinema. There are complaints now about "Solo" because the cinematographer chose to print it very dark so shadow detail is lost in many theatres.

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Fernando Caldeira
Film Handler

Posts: 41
From: Lisbon , Portugal
Registered: Mar 2010


 - posted 06-02-2018 11:59 AM      Profile for Fernando Caldeira   Author's Homepage   Email Fernando Caldeira   Send New Private Message       Edit/Delete Post 
Thnks Dave,

The picture shown is of what it should be. In our projection you couldn´t see much of anything in that frame.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12206
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-02-2018 12:44 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
What size lamp?

You can cheat contrast "a little" by going from a matte-white to a 1.4/1.5 gain screen but you will affect the overall image too. The gain doesn't really improve contrast, that is set by your projector but by forcing a hot spot, you effectively lower the light levels on the sides/corners so it appears you have affected contrast.

If the problem you describe is that you can't see any details on the image you show, then it may be that you don't have enough light to begin with. Contrast ratio is the the measure of the brightest to the darkest and without the image as bright as it should be, you can't improve it.

The focal length of your lens has no effect on contrast ratio. Its design/construction can have an effect but the focal length itself is not an indicator.

Keeping all of the dirt/dust off of the entire optical path from lamphouse, integrating rod, prism and lens will also improve contrast. Anything that causes the light to bounce around hurts contrast and dust will do that.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16221
From: Bountiful, Utah
Registered: Jun 99


 - posted 06-02-2018 01:15 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
I reccomend you only use the actual NEC air flters in the NC-3240. Many of the Chinese variants allow dust leakage around the air filter itself. The NEC filters are expensive, but so is having a light engine properly cleaned...

Mark

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Fernando Caldeira
Film Handler

Posts: 41
From: Lisbon , Portugal
Registered: Mar 2010


 - posted 06-03-2018 09:19 AM      Profile for Fernando Caldeira   Author's Homepage   Email Fernando Caldeira   Send New Private Message       Edit/Delete Post 
Steve,

The lamp is 4.5k. We getting 20fl and bavig a hard time going under.

Mark,
We only use original nec filters

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Mark Gulbrandsen
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From: Bountiful, Utah
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 - posted 06-03-2018 09:30 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
That somewhat explains your problem. 20 fl is way too much light and DLP is not capale of doing absolute black as it is. So I can imagine it looks washed out. You can try defocusing just the lamp focus control (not the X-Y controls) to get light levels down to 14 +/- 2 fl, I tend to set light levels to just under 16 fl. Or try going down to a 3kw lamp. Remember the larger 1.38" DMD chips in that projector are going to put out a bit more light than your average 2K projector does....

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Gordon McLeod
Film God

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From: Toronto Ontario Canada
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 - posted 06-03-2018 10:23 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Nec does have a iris that fits in the patch of the lamp to reduce light and will improve contrast

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Mark Gulbrandsen
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From: Bountiful, Utah
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 - posted 06-03-2018 01:30 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Gordon McLeod
Nec does have a iris that fits in the patch of the lamp to reduce light and will improve contrast
I do not recall one being supplied with the larger projectors, but they may have... There is for sure one supplied with NC-1200 & NC-2000.

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Paul H. Rayton
Expert Film Handler

Posts: 204
From: Los Angeles, CA , USA
Registered: Aug 2003


 - posted 06-03-2018 06:38 PM      Profile for Paul H. Rayton     Send New Private Message       Edit/Delete Post 
NEC definitely does have an iris for their 3240 projector. Accessing the location of said iris is a bit of a project, however. In the case of the 3240 projector, it's necessary to get in by disconnecting some of the rubber coolant piping, and moving away (but not removing) the coolant reservoir. Difficult, but not impossible - but you wouldn't want to do it very often.

So the iris attachment is a very valid approach for improving your contrast, plus it will also drop your screen brightness somewhat, possibly 3 or 4FL, depending some variables. That seems to be good side-benefit for you since you indicate that you're already having difficulties getting screen illumination below 20FL.

We successfully used a similar iris in the NEC model 2500 and it was very good for the image. Sadly, as the optical system aged, the system gradually lost efficiency. After about 6 years we mostly had to leave the iris out because we were having trouble hitting 16FL. That being said, it's also generally accepted that 2K DLP chips have better native contrast than 4K DLP chips, so while it's not practical in your case, you could also achieve a slight contrast improvement going to a 2K projector.

And finally -- those light-colored walls are absolute killers for screen contrast. That's been known for decades, of course, and that's why contemporary high-end cinemas are specified to have dark (or black) walls and ceilings. (The "black box" concept.) I once worked in a cinema that did a refurbishing, including painting the walls and ceiling black, and was astounded by the resulting difference in image quality.

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Leo Enticknap
Film God

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From: Loma Linda, CA
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 - posted 06-04-2018 12:31 AM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
Thanks, Paul. Literally, about the only truly good, "no strings attached" comment I have about the Series 1 NEC compared to the Series 2, is that inserting and removing the iris/depth of field booster plate is so much easier and simpler. The contrast ratio of the 2500 at the Egyptian with the iris in place really looked nice. I remember early one morning watching a Warners' DCP of The Treasure of the Sierra Madre on it shortly after I started working there in 2014: I'd only intended to look at the first ten minutes or so, because our programmer was worried about what it was like. In the event, the sharpness, contrast and gamma struck me as being almost as good as a nitrate print (and certainly better than many of the several 35mm safety prints I'd seen projected), and so I made myself comfortable in the balcony, and watched the whole thing. I'm ashamed to say that this was probably the last time I watched a movie in a movie theater from start to end.

On the 3240 you've got to go in behind the cooling system reservoir to insert and remove the iris, with the result that it's generally considered not worth the hassle, even during 2-D / 3-D conversions. At the Aero it's a Hobson's choice: if you have the iris permanently in, a 4K bulb is perfect for 2-D, but a 3K bulb isn't, and 7K isn't quite bright enough for Dolby 3-D. Without it, a 3K bulb will do (just) for 2-D and a 6.5K will work for 3-D, but the contrast ratio really takes a hit.

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Fernando Caldeira
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Posts: 41
From: Lisbon , Portugal
Registered: Mar 2010


 - posted 06-04-2018 04:53 AM      Profile for Fernando Caldeira   Author's Homepage   Email Fernando Caldeira   Send New Private Message       Edit/Delete Post 
So,

We do have the iris instaled (cat's eye right?) we had about 30 fl before.

Mark,
quote: Mark Gulbrandsen
You can try defocusing just the lamp focus control (not the X-Y controls)
you mean on the back side of the projector right? with the 3 socket screws?

If I reduce the lamp power will it help?

If I need to use a 3k lamp I will need to change the power rectifier right?

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Sean McKinnon
Phenomenal Film Handler

Posts: 1573
From: Peabody Massachusetts
Registered: Sep 2000


 - posted 06-04-2018 10:23 AM      Profile for Sean McKinnon   Email Sean McKinnon   Send New Private Message       Edit/Delete Post 
You could also try a grey or negative gain screen to improve your contrast if the iris alone does not cut it.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12206
From: Annapolis, MD
Registered: Dec 1999


 - posted 06-04-2018 11:16 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Grey screens do not help contrast in a darkened environment. They lower both the top and the bottom (ratio remains the same).

The thing to do after checking with the iris (aka catseye) is to lower the lamp wattage until you are in spec.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16221
From: Bountiful, Utah
Registered: Jun 99


 - posted 06-04-2018 11:19 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
quote: Fernando Caldeira
you mean on the back side of the projector right? with the 3 socket screws?
Yes. Two are X & Y and one is focus or Z.

quote:
f I reduce the lamp power will it help?
You can take it as low as it allows you because the minumum and maximum settings that you are allowed to use are the actual lamp parameters and it's fine.

Yes, you may have to get a different rectifier for a 3kw lamp if you have the 7KW version of the 3240. The rectifiers are directly interchangable with just a simple firmwarte update required so the firmware can properly control that smaller rectifier.

Mark

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