Film-Tech Forum ARCHIVE: 3D to 2D Brightness Adjustments

This is topic 3D to 2D Brightness Adjustments in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Andrew Carr (Member # 9264) on 11-28-2019, 01:52 PM:

For those of you using active polarizers on motorized movers, what is your difference in brightness levels like between 2D and 3D?

I'm looking at a calculation for a theater build that gives me 9.5Fl when the 3D system is in place, glasses included vs. 20Fl when the 3D system is out of the equation.

Are you setting light engine power levels in your projector profiles?

Posted by Dave Macaulay (Member # 813) on 11-28-2019, 04:28 PM:

That depends on the 3D adapter. A Real-D XL will usually give decent ft-L in both 2D and 3D. A Z-Screen will not, the 3D adapter loses too much light so for 6 ft-L in 3D you will have a very bright 2D image even at max vs min lamp power, or a decent 3D brightness and dim 3D.
Dolby 3D is NLA but it eats a ridiculous amount of light.
Yes the lamp power level should be adjusted to suit different formats. All cinema projectors can do this on a per-preset basis.

Posted by Stephan Shelley (Member # 8587) on 11-28-2019, 05:44 PM:

20 ftl is a bit bright for 2D unless you are doing HDR. At that level you blacks are getting very grey.

I know you were asking about polarized 3D but the 6P laser projectors can do a laser 3D based on the Dolby system and you can get 14 ftl per eye with that.

Those projectors are super expensive and very big and need special chillers as well.

Posted by Carsten Kurz (Member # 5396) on 11-28-2019, 06:18 PM:

Well, on a Sony 515 you can operate two or three lamps for 2D and up to six for 3D. Not the worst idea to balance 2D vs. 3D brightness.

On a Barco Xenon, you may use two lighthouses with different bulbs, these can be swapped quickly without readjustment. But as the Andrew talks about motorized movers, swapping lighthouses may be out of the question.

- Carsten

Posted by Emmanuel Nwokafor (Member # 11090) on 11-28-2019, 11:16 PM:

Why not set the light output level on 3D and 2D of your choice, but bear in mind that you must have calculated the appropriate projector type, screen size and throw distant that will achieve such output (don’t try to use NEC NC1000/Barco 10s to have 2D 20FL on a 15m screen size not possible)

Posted by Steve Guttag (Member # 268) on 11-28-2019, 11:44 PM:

Steven, 20fL on a silver (high gain) screen for 2D is NOT overly bright...and probably a bit dark. 22fL would be closer to right. Remember, they are only referencing that in the very middle of the screen...trust me, it won't be anywhere near 22fL on the sides, top or bottom so you need not worry about overly grey images instead of black. If one sets 14fL center on 2D for a silver screen, the image will be overly dark.

Remember, the specification of 14fL in the middle is only valid if you are also 75% of that on the sides/corners (cinemas, 85% in screening rooms). You'll never have that with a silver or any screen over 1.3 gain.

Posted by Sam D. Chavez (Member # 1841) on 11-29-2019, 12:35 AM:

Just to be clear, Stephan was referencing a Barco 6P projector shooting onto a 1.4 gain Harkness screen, not a silver screen. We had a Dolby 3D equipped DP2000 on that screen previously and now a 22L with Dolby 3D. Different 3D glasses to be sure.

Posted by Steve Guttag (Member # 268) on 11-29-2019, 01:40 PM:

The OP's post can be interpreted several ways. First, they use "Active Polarizers" which implies a system like XPAND but what I think they meant was automatic systems that physically move a passive polarization system out of the way (e.g. Real-D with an "XL-Mover.")

If one is using Real-D, the presumption is a silver screen. While Real-D does have a couple of white screens that retain polarization and they are lower than the 2.2-3.0 gain (typical), by far, the norm for Real-D is silver screens and the gains knocking in the 2.4-2.5 range. In that situation, setting the center brightness to 14fL for 2D will result in a dark image.

If Stephen was interjecting the 6P laser into a polarization discussion, that would be his mistake as it only serves as static to this conversation (could be quite valuable to a 6P or other RGB 3-D discussion).

Posted by Andrew Carr (Member # 9264) on 11-29-2019, 03:25 PM:

Thanks for the info, all.

This specifics here will be a Christie CP2320-RGB with a RealD WXL active polarizer. The client wants to show 2D content so the panel will be on a motorized sled.

Screen is 2.2 gain silver surface, 36'W x 19'H with a 54' throw. We run our laser projectors at half power during 3D shows so this leads to a concern that we won't be able to go lower for 2D content.

Posted by Carsten Kurz (Member # 5396) on 11-29-2019, 07:33 PM:

I guess you need to talk to Christie to find out how low you can go with these RGB laser engines.

- Carsten

Posted by Stephan Shelley (Member # 8587) on 12-04-2019, 01:26 PM:

These projectors do not have a overall power/brightness adjustment. You adjust the red, blue and green lasers individually. One needs to use a spectrometer/light meter the continuously updates. You adjust the level and color to get as close to the ideal color and level.

Where you are going to run into problems is the blue laser will only go down to about 35% the red and green around 20%. You can play games and set blue as low as it will go and lower the red and green lower than ideal color and let the color correction fix that and in doing so you will loose additional light with the color correction. Not the ideal situation but can be done.

On the upper end of power it depends a lot on room temp and anticipated room temp. Green is most affected by this as in a hot room say 80 degrees F or more you may be limited to 80% power on green. Take into account that if one runs at max for the temp at start there will be no headroom as the machine ages and gets dimmer.

Posted by Carsten Kurz (Member # 5396) on 12-04-2019, 04:15 PM:

Why do I get the impression that even these second or third generation laser projectors are still premature technology?

- Carsten

Posted by Steve Guttag (Member # 268) on 12-04-2019, 06:53 PM:

Everything is an evolution. I haven't work with the Christie RGB laser so I can't comment on their implementation but even with how manufacturers did their light level, lens adjustment...etc. they took different approaches with varying degrees of WTF?.

I would find it odd to set light level by adjusting the laser's independently. One hope that the manufacturer would know how to scale the colors down as one adjusts and I could understand having to do a MCGD for each light level (same as the HMI lamps). You don't want to "filter" RGB as that is pure waste...just use what you need. So I would hope that these RGB laser projectors, when making an MCGD would not filter in the ICPish board but instead would trim the RGB laser levels.

Posted by Carsten Kurz (Member # 5396) on 12-04-2019, 07:15 PM:

Until now, I was irritated because so many variations of the Christie RGB laser projectors are offered. I guess I understand now.

https://www.christiedigital.com/emea/cinema/cinema-products/digital-cinema-projectors

- Carsten

Posted by Stephan Shelley (Member # 8587) on 12-04-2019, 08:02 PM:

You do different laser files. Same idea as the old lamp files and in some places still referred to as lamp files. Once set there is a light sensor you can turn on for constant light level output. It will then turn up and down each laser proportionately. The idea is you have a intensity and white point for each level needed as a laser file.