my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Digital Cinema Forum   » dcinema install - black level (Page 1)

This topic comprises 2 pages: 1  2

Author Topic: dcinema install - black level Bajsic Bojan Expert Film Handler Posts: 190 From: Ljubljana, Si, Eu Registered: Aug 2008 posted 10-21-2011 12:56 PM                     hello there, we are in the process of installing a dcinema projector in our theater and when it was time for color calibration and light output metering we got some strange (?) results. Color measurements for xyz were within the dci specs for review room, contrast also, uniformity also. The thing that was outstanding was the full white reading of 77 ftL in the middle of the hall. I was really impressed with the picture and everything but the thing that bothers me is the black levels. Black was nowhere near black as it was a darkish grey. I suppose the "greyish" black and the 77ftL go hand in hand, but can something be done about it? Besides changing the bulb. But wont changing the bulb effect the outcome of the color accuracy? pj: Barco 19B lamp: Osram XBO@ 1.9kW screen: HH Perlux 140, 20 by 12 ft (constant width) spectrometer: ?? use: Only 2D!  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 10-21-2011 04:27 PM                     If you do not use 3D, why on earth you have 77fL on your screen??? I do like bright picture and with digital you can afford it because there is no shutter, but 77!! I'd replace the lamp with a smaller one and maybe you do not need a high gain screen if your screen is just 20ft wide. Also, check the overall brightness: particularly if your frame is not curved, you will measure 77fL at the centre, but much much less at sides. Changing the lamp should not affect the colour accuracy too much, the correction is mainly addressing the light path, screen, window and light engine. The lamp colour temperature should not change with a different lamp.  |  IP: Logged Bajsic Bojan Expert Film Handler Posts: 190 From: Ljubljana, Si, Eu Registered: Aug 2008 posted 10-21-2011 05:33 PM                     As i said, i don't need 77fL on the screen, but its there. My question is what will this (the 77 fL) affect and how to change "black" to black (other than changing the bulb)? And since many here have mentioned cinema lamps degrading faster over the first 100 hours especially in dcinema projectors, any info how much that will affect the reading and picture brightness? The screen cannot be changed now, but will probably be changed in the next low period as it has some creases and signs of age. It has been working very well tho for 35mm projection (2.4kW) and video (1.0kW). Thank you for input.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 10-21-2011 06:40 PM                     The standard light level for digital cinema is 14fL. Personally I can't see anything wrong with more light but maybe 77 is too much. The lamp is going to fade and the projector efficiency is going to fade. But you do not need 77fL! I'd aim to 20-ish fL (overall, not dead on centre) so you have some headroom when the lamp ages and then I would eventually replace the lamp with a bigger one over the years if the projector loses efficiency. BTW, have you tried to reduce the power of the lamp from the control panel? You can reduce the power up to 50% approx (not recommended, but you can do it). I'd reduce the power at least at 75% - I think it's the safest position recommended by Christie. The lamp will probably lose 10/20% during the first 100-ish hours, it also depends how you run it. The black level of a DLP will never be perfect, but as you have guessed, the more the light, the higher the black level!  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 10-21-2011 07:39 PM                     What actual lamp size do you have? 1.9kW is not a lamp spec, probably you have a 3kW lamp at reduced power. Barco tends to supply the largest lamp a projector will accept. 77 ft-L is crazy. Naturally the blacks are now dull gray, the DLP has a certain contrast range between off and on, raising the screen brightness raises both white and black levels. At the spec 14-16 ft-L a black screen looks pretty black, but there's a lot of light from the lens if you look into it and you can see a dull greyness on screen in a totally dark auditorium. The Barco B series projectors are very efficient with light, considerably brighter on screen with a given lamp wattage than the C series projectors in my experience. I haven't seen a 19B but the 23B with the smaller lamphouse (than the 32B) still beats a C projector. You had a crooked salesman. A 12C would be the obvious Barco projector choice for you, but the 19B makes him a lot more $$$ on commission. You have absolutely zero reason to go to 4K with a 20' screen - the difference would be invisible - this potential 4K upgrade is the basic advantage with a 2K B projector over a C model. You must reduce the light. Using the smallest available lamp is a start, 1.2 kW is the smallest for a 19B I think. The Perlux screen is also an issue, this is (was when new, anyway) a 1.4 gain surface. A matte white screen will drop the light by about a quarter probably, and give a better image (in my opinion at least). With the 1.2kW lamp you should be in the ballpark, but try the lamp first. If it's still 40+ ft-L you may want a smaller projector or you can get lower reflectivity screens. Using a ND filter is an option but you are wasting money and energy that way.  |  IP: Logged Olivier Lemaire Expert Film Handler Posts: 118 From: Paris, Ile de France, France Registered: Jan 2010 posted 10-21-2011 09:34 PM                        quote: Marco Giustini BTW, have you tried to reduce the power of the lamp from the control panel? You can reduce the power up to 50% approx (not recommended, but you can do it). I'd reduce the power at least at 75% - I think it's the safest position recommended by Christie. You can reduce the lamp wattage until the "minimum watt" for a given lamp. So YMMV with lamp models. For example, with a 2 kW lamp with 1 kW minimum wattage, you could drop at 50% maximum. With a 3 kW lamp with 1 kW minimum wattage, you could drop at 33%. The key is that you cannot drop lower than the lamp minimum wattage, afaik.  |  IP: Logged Jussi Siponen Film Handler Posts: 75 From: Mikkeli, Itä-Suomi, FINLAND Registered: Jan 2010 posted 10-22-2011 02:02 AM                     This may depend on the xenon bulb, but at least with Ushio bulbs installed on a Barco projector I've been able to adjust the lamp power between 60% - 100% of the nominal power. Bajsic reports 1.9kW lamp power, the power of a fully dimmed 3kW would be about 1.8kW so his 19B is very likely equiped with the largest (3kW) bulb a 19B will accept. Dave is correct about 1.2kW being the smallest bulb for a 19B. Doing the math, a 1.2kW bulb would give you 49 fL on full power and 29 fL fully dimmed -- which would be very nice for 3D, but is way over spec for 2D. You may have to use the smalles bulb *and* intentionally de-focus the bulb just a little. Oh, did you measure the brightness *after* color calibration or was this done using "engine white"? If it was, the color calibration is going to drop your peak white levels some, so you might be good even without de-focusing the bulb. What an odd situation to be in -- at least you will have *fantastic* 3D if you ever start showing it...  |  IP: Logged Bajsic Bojan Expert Film Handler Posts: 190 From: Ljubljana, Si, Eu Registered: Aug 2008 posted 10-22-2011 06:08 AM                     thank you all for the input. no, the 4k upgrade option was a must from the management, so the C series was never a question. Yes, for the initial tests a 3kW lamp was factory installed (i have 2kW replacement bulbs i ordered because i figured the 3kW will be way too much), which was dropped down to 1.9kW (minimum), color calibrated using a spectrometer, then the full-white light output was measured @ 77ftL. Is it good to assume light efficiency will go down by about 20% in the first 100 hours? So, i should do things in this order: - change the 3kW bulb for a 2kW (or lower) and drop it to minimum - replace the Perlux with a microperf Matt white eventually How much can reflected light effect the readings? I am asking because we have a 'reflective' hall with lots of red and gold ornaments (1920s theater). How much can bleed from the sides of the projection lens affect the readings? I have heard it is advisable to mask the porthole as much as possible to reduce reflections and stray light. Would that improve things? Thanks  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 10-22-2011 08:09 AM                     Light coming back off the hall will affect contrast but not the black level, the low light at black (even wen it's gray) won't reflect back enough to matter. You want to achieve as close as possible to total darkness in the auditorium. There are obvious safety problems with that, so we have to live with Tivoli lights (or whatever) and lighted exit signs. If the booth is dark, the port shouldn't be an issue. Reducing needless light in the booth and painting it a dark color works well. basically if there's nobody up there you don't need lights and if there is somebody up there they must need to see the screen. Using a low reflectivity screen is an option if you have a lot of re-reflected light from a light colored auditorium. This requires extra projector light so it's rarely used in normal cinema, but domed theatres and deep curved screen installations use screens with quite low reflectivity - I think Omnimax was using 0.4 domes when I was installing them. You certainly have lots of extra light. Really, 4K on a 20' screen? That salesman definitely gets a coffee.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-22-2011 10:46 AM                     Remember, 4K is only 35mm 1.85 resolution. It isn't like it is too absurd on a 20' wide screen...just not what I would consider top priority. I too have been "forced" to install a 4K machine on what I would consider a "small" screen. The picture does look fantastic and I really like the small pixel size. As for the light issue...The goal should be a matte-white screen in all applications, if at all possible. The highest gain should be about 1.3 or you will fall out of spec on the sides/corners. The Harkness Perlux 1.4 is notably hot-spotty too. The spec is 14fL. Despite what some may think, the contrast ratio of the DCinema machines is not that of film and as you go above 14fL, your blacks WILL become gray. That 2000 contrast ratio they like to brag about is not what the projector can do with both bright and dark presented at the same time. It is a bogus number...the real contrast ratio is closer to about 500 or less than half of film's capability (note I said capability...there are some decidedly crappy prints)...not too worry, most fire codes prevent cinemas from even achieving 800:1 Since you have a gain screen, you should probably elevate your center brightness point a bit above 14fL...shoot for 18fL...you will have less black level in the center but overall it should look pretty decent. I think I have a recording of a Harkness Perlux 1.4 somewhere...if so, I'll run the numbers and see if I can come up with a good target center brightness. In the meantime...definitely lower your xenon lamp size...even a 1.2KW lamp should be sufficient (caution...I did not run the numbers on it...just a gut instinct). Changing lamps should have minimal affect on color reproduction, don't work about recalibrating on a per-lamp basis. The xenon light spectrum is pretty uniform. Things like screen, reflector, lens, port all have more effect on the color. -Steve  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 10-22-2011 10:53 AM                     quote: Dave Macaulay You have absolutely zero reason to go to 4K with a 20' screen - the difference would be invisible - this potential 4K upgrade is the basic advantage with a 2K B projector over a C model. Not to get too far off-topic here, but I thought I remember hearing or reading somewhere that all Series 2 are upgradeable to 4K. If this is not the case, then what determines whether the projector is upgradeable or not?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-22-2011 10:55 AM                     For now the existing DMD size of the projector is what determines if it can be converted... also it HAS TO BE a series 2. So conversions are limited to 1.2" projectors. The 4K DMD's are 1.38". It would be a manufacturing miracle if they manage to fit 8.4 million moving mirrors onto a .89" chip/  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 10-22-2011 11:10 AM                     So is 1.2 vs .98 the difference between the B and C series? I'm not nearly as familiar with the Barco products as I would like to be. If the light engine of a C series currently uses .98 DMD's, why can't the entire light engine just be swapped to upgrade? Is there something else that limits the C series to .98? EDIT: The Features tab on the product page for the 20C says, "Next-generation electronics ready for DLP Cinema® Enhanced 4K (dependent on availability of DLP Cinema® Enhanced 4K 0.98” DMD from Texas Instruments)." So in theory, they could make a 4K .98 DMD, correct?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-22-2011 12:21 PM                     Starting at the mirror and ending at the front lens element... the two types of projectors are completely different. Not at all compatable with each others parts...  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 10-22-2011 02:25 PM                     From the Features tab of the 20C product page: "Easy installation and maintenance thanks to proven modular design and common platform with DP2K B-series." So this begs the question of what they mean by "common platform." Are not at least some of the components common across both series?  |  IP: Logged

All times are Central (GMT -6:00)

This topic comprises 2 pages: 1  2

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.