Film-Tech Forum ARCHIVE: Screen Gains and contrast

This is topic Screen Gains and contrast in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Doug Woods (Member # 8000) on 01-30-2014, 05:17 AM:

Hey there, not sure if this is the place to ask this question, however...

I'm setting up a DI (digital intermediate) colour correction studio with a Christie Solaria One and I would like to get opinions on the best screen gain to achieve the best contrast.

The throw is 25 ft to a 105 inch wide screen. I will be replacing the screen with a little larger one when I determine the most suitable materials.

I currently have a 1.1 gain screen and the blacks feel a little washed out especially compared to the LED LCD monitors.

I can achieve total darkness, except for my computer interface monitor.

If anyone has experience with this I'd love to hear it.

Thanks
Doug

Posted by Carsten Kurz (Member # 5396) on 01-30-2014, 06:05 AM:

The Solaria one is brightness, not contrast optimized. Black levels on all current cinema DLPs are not optimal, with the 1.2" models being the best in that respect and the S2k models being the worst.
A gain screen will make it even worse. If you have enough brightness for your screen size, you may go with a matt grey screen surface (negative gain), and if possible you should use the lens in it's tele position, that is, place the projector the farthest away from the screen.

- Carsten

Posted by Brad Miller (Member # 2) on 01-30-2014, 11:23 AM:

Christie offers high contrast lenses as well as a high contrast kit. I'm know Barco does not and I don't think NEC does either, but I'm not 100% sure on NEC. Go with the CP2215, get the kit and the high contrast lens. You will find the image is vastly superior to the typical result.

I try and use high contrast lenses whenever I can, but on occasion where I've got light to spare I'll put the high contrast kit in as well. I've never done it in a CP2210/2215, but I believe that is an option.

Posted by Carsten Kurz (Member # 5396) on 01-30-2014, 11:44 AM:

Well it seems that even the 'tuned' postproduction versions of the Christies and Barcos only achieve something like a 10-15% improvement in contrast/black level (at something like 50% less light efficiency).

http://www.barco.com/en/Specsheets/32b82c40-301e-4c30-a650-fa1db2244d0c/DP2K-P.pdf

That is near to nothing. And I wouldn't even start to think about a 4k:

http://www.barco.com/en/Specsheets/9c7e0fc6-b4f3-4efc-bd34-4de6d1a38287/DP4K-P.pdf

- Carsten

Posted by Alan Gouger (Member # 543) on 01-30-2014, 12:16 PM:

Brad what is the Christie "contrast kit" comprised of. Nice to see them offer this.

I took a Barco 4kP HC lens and replaced the factory iris with a more aggressive cats eye iris along with an aggressive iris in the light pipe just after the lamp house. I achieved 4000:1 maintaining uniformity. Most of the increase comes from the iris in the lens. The trade off is light loss, 40 to 50% but the increase in PQ is visually noticeable.
If a laser retro ever becomes available those numbers may increase due to the nature of laser and its tight beam.

I measured a Sony SRX515 over 8500:1 out of box, Minolta meter, impressive. PQ is vastly improved over the SRX320.

Posted by Steve Guttag (Member # 268) on 01-30-2014, 02:34 PM:

So you measured, with a 14fL center, on a checkerboard pattern, .001647fL or thereabouts?

Forget the checkerboard pattern...you measure that with full on and then full off? What is the accuracy of your meter?

Posted by Alan Gouger (Member # 543) on 01-30-2014, 04:20 PM:

Im using both a Photo Research "Cinebrate" for readings off the screen and Minolta T-10 for readings back at the projector.Yes full on/off is used.
My clients have private screening rooms with complete light control to take advantage of any extra contrast.

Posted by Marco Giustini (Member # 4544) on 01-30-2014, 06:26 PM:

If you want higher contrast, you should get a Sony 515. Contrast ratio is waay higher than DLP.

Posted by Carsten Kurz (Member # 5396) on 01-30-2014, 06:42 PM:

And the new SRX-R510 is no more expensive even at 4k than the Solaria One.

However, it lacks the necessary interfaces for a grading suite (2k/4k xyz only through DCP, only HDMI 1080p for external sources).

The SRX-T615 would be better suited, but is waay more expensive (for no apparent reason ;-)

- Carsten

BTW - Marco, did you read my private message?

Posted by Steve Guttag (Member # 268) on 01-30-2014, 06:51 PM:

I'm confused...you are using an incident meter to measure contrast ratio off of a screen? I guess you are holding the meter up to the screen, measuring full on and then measuring full black.

The Cinebrate tops out at 1000:1 contrast ratio...and that is if you hit the center at 50fL.

And it is all BS anyway...put up an alternating checkerboard pattern and see what you have.

Posted by Doug Woods (Member # 8000) on 01-30-2014, 08:25 PM:

WOW, what an active forum. I love it.

Thanks for all the suggestions.

So I'm looking into the contrast kit for my projector as I have plenty of light to spare with the .3 ND filter and bulb at 59% to achieve a 14 fl reading.

2 important questions.

1 Do you know if screen manufacturers supply sample pieces, swatches, to test the various screen gains before you commit to a screen?

2 How do I embellish my "film handler" handle in my profile.

Posted by Dave Macaulay (Member # 813) on 01-30-2014, 08:46 PM:

You should be able to get sample pieces from the screen people, I have definitely seen them. Ask!

The member rating/description is based on post count, I don't know how many posts are required for each level. Probably Brad can override that and even put oddball ones in if he wants, not sure about that though.

Posted by Alan Gouger (Member # 543) on 01-30-2014, 08:58 PM:

The meter is place facing the lens close enough to get a solid reading between full on and off. Checker board is used to measure ANSI contras not on/off.

Posted by Carsten Kurz (Member # 5396) on 01-30-2014, 09:01 PM:

quote: Alan Gouger
Im using both a Photo Research "Cinebrate" for readings off the screen and Minolta T-10 for readings back at the projector.

I guess Alans 'off the screen' means 'pointing the Cinebrate to the screen', reading screen luminance, while 'back at the projector' means he is holding the T-10 at the screen level pointing 'back towards the projector' reading incident light level on the screen surface. I first got it exactly the other way round...

- Carsten

Posted by Alan Gouger (Member # 543) on 01-30-2014, 09:09 PM:

Yes the PR takes its reading off the screen. The T-10 faces the projector usually a foot from the lens. You need enough light at 0ire to excite the meter. For best accuracy using an illuminance meter measurements between full on/off should be taken from the same distance to the lens.

Posted by Marco Giustini (Member # 4544) on 01-31-2014, 07:10 PM:

Yes Carsten,

I have replied today.

Posted by Christopher Woollard (Member # 2455) on 02-08-2014, 06:39 AM:

The new NEC laser digital cinema projectors are about to launch. The prototype has vastly improved contrast over xenon illumination. Possibly wait until you can review this technology. The others will follow in short course. We had a demo of laser projection over here in the UK at Pinewood, stunning but likely to be very expensive. I have exactly the same problem with digital projectors. You could talk with Harkness regarding their high contrast grey screen. They do provide screen samples.

Posted by Alan Gouger (Member # 543) on 02-08-2014, 10:57 AM:

Christopher would that be the smaller unit similar to the NC900C or the full size projector. Thank you.

Posted by Christopher Woollard (Member # 2455) on 02-08-2014, 12:37 PM:

Hello Alan
The projector we saw was a prototype. Very small producing superb quality images.
The projector was even smaller than the NC900C.
We were informed the first commercial laser projector from NEC would be the NC1100L, suitable for up to 11m screens (1.8 gain) with the same media block as the NC900C. No one mentioned a price but the launch is due for March. I hope the BKSTS can do an event for it as everyone will be interested.

Posted by Bajsic Bojan (Member # 4928) on 02-08-2014, 06:08 PM:

while on the topic of screen gain.

For 3D polarization purposes, should one look at the screen gain primarily or the extinction ratio? They seem to be correlated and the later is also lower, as apparently no silver screen is 100% polarization-proof. Does this play an effect on the measured brightness of the reflected light through passive (realD) glasses and how much.

Does it effect contrast also? I cannot find anything useful on this subject here or elsewhere on the net.

Thanks

Posted by Carsten Kurz (Member # 5396) on 02-08-2014, 07:44 PM:

quote: Christopher Woollard
vastly improved contrast

If so, wondering why NEC is advertizing a mediocre 1600:1 for it?

http://www.necdisplay.com/documents/PressReleases/NC1100L_PressRelease.pdf

This is an S2k machine, and it seems the light engine is not optimized for laser illumination. As such, the S2k chipset seems to be the limiting factor.

- Carsten

Posted by Dave Macaulay (Member # 813) on 02-08-2014, 08:41 PM:

Screen gain on a silver screen for 3D is best decided with the auditorium and screen/projector geometry in mind. Higher gain means more directivity and more hotspotting. For a "shoebox" cinema with the projector close to the screen centre a higher gain screen is generally good. For a stadium cinema or larger conventional room, higher gain will result in a worse hotspot and poor image brightness outside a triangle with the point at front row centre. A curved screen will help in a wide house and tilting the screen appropriately helps where the projection point is far above screen centre. In my opinion lower gain looks better, but economically the brighter projector needed might kill that deal. The laser systems have been touted as brighter and potentially ideal for larger 3D venues; although the TCO difference is not clear as of yet you may want to think about laser. Although there are other issues (such as initial cost, glasses loss, and the need for a cleaning system + procedures), any non-polarized 3D system gives a superior image (again, just my opinion).
As far as extinction ratio - no system is perfect and I haven't seen a huge difference specified between systems. With polarized systems the screen deteriorates over time and specs will be for a best case screen. The Dolby and various shutter glass systems don't have that degradation of extinction ratio with screen aging. Every screen, 2D or 3D, loses brightness as it ages and gets dirty. Other than very careful dust removal I don't believe there is any way to clean a silver screen successfully. Matte screens can be cleaned but results are unpredictable and a new sheet is usually the better solution - and matte screens are much cheaper that silver to replace.

Posted by Mark Gulbrandsen (Member # 72) on 02-10-2014, 02:03 PM:

I found out last week that the NC-1100 has a projected list price of around 45K USD.