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» Film-Tech Forum   » Operations   » Digital Cinema Forum   » How Many Lumens? (Page 1)

 
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Author Topic: How Many Lumens?
Robert E. Allen
Phenomenal Film Handler

Posts: 1078
From: Checotah, Oklahoma
Registered: Jul 2002


 - posted 08-01-2003 10:21 PM      Profile for Robert E. Allen   Email Robert E. Allen   Send New Private Message       Edit/Delete Post 
I am considering using a video projector in my upcoming project. I'm looking at a model that puts out 3500 lumens. It will be a 35 foot throw to a 9' x 22' screen. Will that be enough light. Also, since I've never used a video projector I would like to know how it adjusts for the different formats.

Thanks.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 08-01-2003 10:28 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Likely you will be projecting a 1.25:1 aspect ratio graphics image, so your actual image size (assuming the lens you have lets you) will be only about 11 x 9 feet, or about 100 square feet. So a 3500 lumen projector should theoretically give you about 3500/100 = 35 footlamberts on a matte white screen --- more than bright enough. It probably will be less, as the rated output is, shall we say, usually "optimistic".

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12207
From: Annapolis, MD
Registered: Dec 1999


 - posted 08-01-2003 11:13 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Just curious...John...why do you say it will be a 1.25:1 image? Did I miss something in the original description.

In the video world...there are only really so many "native" formats.

For "data"...that is stuff that is computer in origin (like Power Point) then you have the resolution of the computer which can be all over the place. Most video projectors today fall in to the XGA 1024 x 768 category (4:3 aka 1.33) or the SXGA 1280 x 1024 (5:4 aka 1.25).

Thus if you are projecting data, then John is quite correct that you will more than likely be working with a 5:4 image..if your projector is a 4:3 native XGA machine than you will not be using all of your horizontal pixels.

For what I call motion video (DVD, DigiBeta, HDCAM, D-5...etc even VHS) you really only have two "native" ratios to worry about that have any real standard. 4:3 (essentially everything prior to HD) and 16:9 (essentially anything HD in origin, including some of the 16:9 enhanced DVDs).

Most large bright video projectors do not have 16:9 displays though they can be made to project that image. Even the current crop of DCinema projectors from Christie and Barco are really 5:4 SXGA projectors that have to be told what the native image is of the source selected and then an appropriate anamorphic lens is used to expand the image, just like scope for film.

Lets say you get one of the current crop of XGA native projectors out there. You have a 4:3 native image. If you are going to run either data (5:4) or 4:3 material, you are fine. If you plan to run 16:9 (or any ratio wider than 4:3) you have choices to make. Many people merely zoom out the picture so the letterboxed image fills the height. This brings about several negative aspects. First, you just enlarged the pixels so the picture will look worse (just like FLAT for film); second, you picture brightness just went down. Using similar numbers to John (remember my example was with a 4:3 machine) your 4:3 picture was at a theoretical 32.4fL (nice, by the way, for high-ambient light power point shows) down to something like 18fL...still not bad but nearly half of what you had.

Lets presume you want to run some DVDs that will have 1.85 or 2.39 scope titles...now you are going to really zoom out (most likely you wont be able to find a zoom lens that will allow this much range...normally there is one narrow sweet spot in a zoom lens' range where you can get 4:3 and zoomed 16:9 with one lens and one projector location. Your theoretical scope image is down to around 10fL. Most of your "light" is now lighting up black pixels. And to add insult to injury, if you need to read any of the menus to set up your projector prior to show...they will be on the ceiling and floor. You will also see just how unblack those pixels are.

An alternative is to use an anamorphic lens for your video projector. ISCO makes lenses for a large quantity of video formats including 4:3 and 5:4 native format projectors. Using them, you can keep your resolution and brightness. I'd put the money into the anamorphic lens and get a less bright projector that will be cheaper to maintain or run a 3500 lumen projector at half brightness (most projectors have an energy save mode). In this manner, you can have the REALLY bright picture for Power point in high-ambient light situations but maintain a great picture with reduced lamp cost in movie mode.

Check out ISCO Anamorphic DLP/LCD Lenses

Steve

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 08-01-2003 11:37 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
quote:
why do you say it will be a 1.25:1 image
Just had 1280 x 1024 pixels on my mind.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12207
From: Annapolis, MD
Registered: Dec 1999


 - posted 08-02-2003 12:15 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
And just what color are those pixels? [evil] [Wink]

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002


 - posted 08-02-2003 04:30 AM      Profile for Michael Schaffer   Author's Homepage   Email Michael Schaffer   Send New Private Message       Edit/Delete Post 
quote:
Just had 1280 x 1024 pixels on my mind.

That reveals John as a Macintosh user.

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002


 - posted 08-02-2003 05:09 AM      Profile for Daryl C. W. O'Shea   Author's Homepage   Email Daryl C. W. O'Shea   Send New Private Message       Edit/Delete Post 
John uses an IBM Thinkpad, and (based on his login ID) his system administrator at Kodak is twisted, although apparrently good at what they do. Well maybe not twisted, but certainly out of the ordinary.

I run 1280x1024... I never use Mac's anymore.

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Jon Bartow
Master Film Handler

Posts: 287
From: Massachusetts
Registered: Nov 1999


 - posted 08-02-2003 07:07 AM      Profile for Jon Bartow   Email Jon Bartow   Send New Private Message       Edit/Delete Post 
I also use 1280x1024 and never use a mac (with the rare exception of some occasional video editing for my church at a nearby studio.
Jonathan

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Clayton Shedd
Film Handler

Posts: 1
From: New London, NH, USA
Registered: Apr 2003


 - posted 08-02-2003 10:11 AM      Profile for Clayton Shedd   Email Clayton Shedd   Send New Private Message       Edit/Delete Post 
i'm looking to show movies on the town green. i would start just a tad before dusk and am told i should use a 3000 lumen projector. indoors, with lighting half or more dimmed, 3500 lumen would be major overkill and very pricey.

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Gordon McLeod
Film God

Posts: 9460
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 08-02-2003 10:16 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Not all manufacturers have always used the same method of determining lumen output

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 08-02-2003 01:07 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
Actually, I was thinking of the 1280 x 1024 DLP chip.

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002


 - posted 08-02-2003 05:31 PM      Profile for Michael Schaffer   Author's Homepage   Email Michael Schaffer   Send New Private Message       Edit/Delete Post 
quote:
Actually, I was thinking of the 1280 x 1024 DLP chip.

That reveals John as a DLP user.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000


 - posted 08-02-2003 06:11 PM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
quote:
That reveals John as a DLP user.


I didn't say that I was thinking good thoughts aboout the DLP chip. [Wink]

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Frank Angel
Film God

Posts: 5198
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 08-03-2003 05:13 AM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
Something smells rotten in videoland. First off, how come video hardware manufacturers have decided that the decades old SMPTE standard for evaluating overall brighness -- using foot lamberts -- is not good enough for video projectors? Perhaps it's not quite as easy to fudge foot lambert numbers? Here's my problem: seems to me there is something amiss in their Alice-in-Videoland world when you can say a projector with 3500 lumens will produce an image equal to 35 foot lamberts, more than double what would be considered a very bright image from a 35mm projector reaching the 16ftL benchmark. Then to confound even more, I just saw a demo of an Eiki LCD projector in our theatre which is rated at 11,000 lumens (that's eleven THOUSAND boys and girls) and low and behold, it was slightly less bright than our 35mm screen brightness, which is just under 16ftL. So is there something wrong with the math here or are the manufacturers simply making these lumen numbers up? According to John's calculations, a projector rated at 11,000 lumens shoud be able to put out 110ftLs? How is this possible? Besides, I can't understand how a projector with a 250 watt lamp can produce a brighter light output than a xenon arc lamphouse burning 2000 watts, notwithstanding the difference in aperture sizes.

And while I am at it, what's with this irrational abandoning of the decades old methodology of stating aspect ratios? For eons the simple declaration of width-to-height has been the norm. It is clear; it is directly understandable without any mental reconfiguring. Height is always 1; the width is always the variable. It is immediately accessable to the mind's eye. Did the vidiots think 16:9 is more understandable than 1.78:1? or 4:3 or 5:4, or are they just afraid of fractions? What are they going to do if they alter a format slightly like we had to do with scope -- 2.55 became 2.35 became 2.39, etc. What kind of bizzare non-fraction ratio are they going to have to come up with to express a small change like that? IMHO, it would have made a lot more sense if they had continued our perfectly workable and elegant way of expressing aspect ratios, even if it IS used by film people. We are not the enemy.


Frank

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Bernard Tonks
Jedi Master Film Handler

Posts: 619
From: Cranleigh, Surrey, England
Registered: Apr 2001


 - posted 08-03-2003 06:47 AM      Profile for Bernard Tonks   Email Bernard Tonks   Send New Private Message       Edit/Delete Post 
quote:
Besides, I can't understand how a projector with a 250 watt lamp can produce a brighter light output than a xenon arc lamphouse burning 2000 watts, notwithstanding the difference in aperture sizes.
Exactly Frank, that has also been bugging me for a long time now. Our local Arts Centre with a spacious 130 seat auditorium uses an Eiki LCD projector with a 250 watt lamp and the light is remarkable for the size of the 4x3 ratio screen. Wide & scope pictures are of course letterboxed, but they get away with it! Films are run 1-2 nights a week which used to be on 16mm, but now only available from the distributors in DVD format.

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