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Author Topic: Lumens Question Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 03-27-2014 08:52 AM                     One of my auditoriums is very small (37 seats). I am considering getting a BenQ projector that puts out 2700 lumens for playing DVDs & BluRays. The screen is 20 feet wide. Is 2700 lumens bright enough?  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 03-27-2014 09:06 AM                        No. The math is essentially this: 8.5' x 20' = 170 square feet of screen, assuming a common-height 2.35:1 screen. Footlamberts = lumens per square foot on a 1.0 gain screen, so 170 x 16 = 2720 lumens needed, assuming a 1.0 gain screen. The video standard is 14fl, but you should probably shoot for 16. The problem is that the video projector is probably using a 16x9 chip, not a 2.35:1 chip, so the actual size picture that it would need to project for a scope image is 11.2 x 20, which means that you really need 3584 lumens for scope and just over 2000 lumens for 16x9. Additionally, most video projectors are pretty optimistically rated for light output, using the most favorable lens and new lamps. Especially with mercury lamps, the light output can drop by half over the life of the lamp, with the result that you really want a 7k lumen machine for that size screen or else you need to consider a gain screen surface. Before buying something like this, get a rental or demo machine with similar specs and the same lens that you plan to buy and try it on your screen to make sure that you have the right lens and that the picture is sufficiently bright (recognizing that light output will decrease over the life of the lamp). Make sure that the lens that you have can zoom to accommodate 1.37, 1.66, 16x9, 1.85, and scope images on your screen with whatever masking system you have.  |  IP: Logged Edgar Prass Film Handler Posts: 32 From: Tartu, Tartu county, Estonia Registered: Mar 2013 posted 03-27-2014 01:06 PM                     I have a similar issue but the question is rather how much is too much? We are about to move our main video projector to a smaller auditorium and based on Scott's math above it would give a max brightness of 28fl (just installed a new mercury bulb). Some days ago I tested the projector in the small auditorium and I would say that the image was "nice and bright", but would it become exhausting for eyes after some hours? Projector also has an eco-mode, perhaps should use that and save some lamp hours.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 03-27-2014 03:18 PM                     I am not aware of any projectors that use true 2.35 chips in them. Perhaps there is an LCD model that does but All the Dee L Pee projectors I am aware of have 16 X 9 chips. Also, you should really measure the gain of your actual screen. If it's old it is probably less then 1.0 if it was a matte surface. Spectra FL meter and reflectance standard is all you need to measure it. Mark  |  IP: Logged Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 03-27-2014 10:29 PM                     Scott: I was mistaken about the screen size. It's 8 x 12. The contrast ratio of the projector is 10,000 to 1. Does that make any difference?  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 03-28-2014 10:58 AM                        It makes a big difference! Assuming a 1.0 gain screen, 2K would exceed the actual requirement, if you can get 2k lumens throughout the life of the lamp and with the lens that you are using.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 03-29-2014 10:12 AM                     If that reads 3,65m*2,43m, then it is possible to throw a nice and bright picture on it with a decent home video projector. Not any Benq is suited though. I prefer JVC or e.g. a Panasonic AT6000/AE8000. These also have motorized, presetable lenses with a wide zoom and shift range. These two are also very quiet, if you plan to mount them in the auditorium. - Carsten  |  IP: Logged Mike Frese Master Film Handler Posts: 465 From: Holts Summit, MO Registered: Jun 2007 posted 03-29-2014 06:54 PM                        How many of you feel that this a wise investment for this theater to do? Would it not better to save the money for a switch to a real DCP cinema projector? So few theaters are able to make a decent amount of money on playing movies on dvd. Those tend to be arthouse type theaters (who seem to get away with having a very small screen) in large populations. I have not heard of any rural theater in a small town of 3500 people do well playing movies on dvd.  |  IP: Logged Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 03-29-2014 07:21 PM                     As the folks put it around here Mike we are "...in the country". It is our plan to play on our 12 foot screen classics from the 30s, 40s, 50s & 60s.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-30-2014 06:32 AM                     I can only stress out what Scott said: the lumens claimed by many manufacturers are seriously over-optimistic. First, they do not consider any calibration. So a 3000lumen figure could mean "3000 lumen with severely yellowish colours". Some projectors slide an extra filter in for the MOVIE preset, to make colours more accurate, reducing the light output. Contrast is another catch: they will claim anything and usually those figures are far from being true. While JVC DILA are superb at ON/OFF contrast, they are not great at ANSI contrast. A typical JVC contrast ratio can be 20.000:1 ON/OFF, but just 120:1 ANSI. And lamps: those lamps will drop considerably over time. Meaning that the brightness figure already overenthusiastic I mentioned will only happen when the machine is brand new. Bottom line: don't be fooled by the numbers on the box, check a professional review first. I also recommend JVC, they do really deliver a brilliant picture. It should be enough on a 3.5m screen, but you may want to replace the lamps a little more often to offer a good brightness on screen.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 03-30-2014 01:11 PM                     quote: Mike Frese How many of you feel that this a wise investment for this theater to do? Would it not better to save the money for a switch to a real DCP cinema projector? That would be true for an investment in the 10.000US$ range. A suitable home-video projector for a 3,60m screen can be bought below 3000US$ (and will usually show a better picture quality than a S2k DCI machine). This is 3.000US$ vs. 30.000US$. - Carsten  |  IP: Logged Mike Frese Master Film Handler Posts: 465 From: Holts Summit, MO Registered: Jun 2007 posted 03-30-2014 05:07 PM                        quote: quote: Mike Frese How many of you feel that this a wise investment for this theater to do? Would it not better to save the money for a switch to a real DCP cinema projector? That would be true for an investment in the 10.000US$ range. A suitable home-video projector for a 3,60m screen can be bought below 3000US$ (and will usually show a better picture quality than a S2k DCI machine). This is 3.000US$ vs. 30.000US$. - Carsten Carsten, Yes the cost for a home projector is cheap vs a DCP projector. You can pick one up for less than $1000. But........ My question is will enough people come in this small rural Oklahoma town of less than 4000 people to make this worthwhile? I have not seen a small town theater who normally plays mainstream movies do well with old movies. Would it not be better to keep playing movies on film even if they are 10-12 weeks old? Who knows of a theater that does well playing old movies on dvd that is in a small rural midwestern town? I know some theaters in cities can do well with these old movies on dvd. Instead of spending $1000 on a home video projector that may not make any money for the theater, put that money to your digital fund. Andrew Thomas has shown examples of being able to go digitl for just $6,000 down.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 03-31-2014 09:37 AM                        Scott, thanks for that formula -- very helpful. Sounds like Robert has thought out the viability of an arthouse formula for his small auditorium, so let's treat that as a given. The question still remains, is a consumer projector going to work for that situation. And that will hinge on what you want to accept as "OK," given you have accepted that the less-than-professional-standandards of DVD are acceptable (which may very well work on such a small screen). But let me say that with a similar size screen of 22ft, we are using a three chip LCD Eiki at 10,000 lumens on a high gain screen and I can tell you my eyes are still asking for a brighter looking picture, but for the purpose of this room, it did what was necessary when we need to show other than 35mm content (which now is most of the freaking time). That said, let me add, the choice came after multiple trials with a variety of projectors from the cheapest to this Eiki - probably the most expensive one we tested - before eveyone agreed this would be "OK." It cost over $20,000 with proper long throw lenses; this was no $3,000 toy. So yes, you can get a workable image from a non-DCI compliant video projector, but don't think you will be happy with one of those home theatre jobs; expect to spend what comes close to buying a real digital unit like the digital-lite units by Christie and Barco, which you might want to consider going for if you really think this room will make a profit; if it is just a kind of throw-away thing you want to do to augment the main house and as a kind of public service marketing thing, then a consumer projector would work, but still, expect to spend some bucks if you want an image that won't scream, "Projectionist -- your carbons are forever going out."  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-31-2014 11:23 AM                     any chance your eyes are looking for more contrast ratio instead?  |  IP: Logged Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 03-31-2014 04:52 PM                     Thanks for your input Frank. Bob  |  IP: Logged

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