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Author Topic: Suggested xenon wattage
Andrew McCrea
Jedi Master Film Handler

Posts: 645
From: Winnipeg, Manitoba, Canada
Registered: Nov 2000


 - posted 05-09-2006 11:59 PM      Profile for Andrew McCrea   Author's Homepage   Email Andrew McCrea   Send New Private Message       Edit/Delete Post 
So here's the calculations:

 -

Please don't scold me for the measurements (because the room is almost square), this is just a 'hypothetical' cinema.

What size xenon do you think would be appropriate for each screen?

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999


 - posted 05-10-2006 12:08 AM      Profile for Aaron Sisemore   Email Aaron Sisemore   Send New Private Message       Edit/Delete Post 
Depending on the lamphouse or console used, either a 2K or 3K would be ideal for those. I'd lean towards 3K for #1 anyway.

-Aaron

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
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 - posted 05-10-2006 12:10 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
True, 3k, or at least 2.5k for the Cinema 1 house...with that bigger scope screen

But, the other one more towards the 2k bulb..

and recommend Christie SLC consoles..or the SLH lamphouses..

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Andrew McCrea
Jedi Master Film Handler

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From: Winnipeg, Manitoba, Canada
Registered: Nov 2000


 - posted 05-10-2006 12:23 AM      Profile for Andrew McCrea   Author's Homepage   Email Andrew McCrea   Send New Private Message       Edit/Delete Post 
Thanks.

At first, I was thinking 2kw would be more than enough, but then I realized the short throw onto a screen of similar size.

Because this was designed for a small town I had in mind (my little secret), #1 would seat 106 and #2 would seat 57. The idea (even though the floor would be sloped, not stadium) was to design the auditorium to provide the wall-to-wall screen in-your-face experience, like a big-city multiplex. And, I made sure that the screen was maxed in scope, with a short ceiling height, kind of too mimic one of my favourite theatres.

The lamphouse would probably be a used Super Lume-X or Super 80. Is there anyway that both could have 2500 or 3kw, and a shutter or something that could cut back the light in #2? That way, you're only stocking the same parts for the same lamphouse, with the same bulbs.

I was thinking a Simplex XL.

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
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 - posted 05-10-2006 12:52 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Super Lume-X lamphouses can do 2.5k bulbs at the max...Even, a Super 80 can go down to a 2k bulb.

..anything but not to shutter down any light - wasting your time and money in doing this.

I'd go for the Super 80's due to their versatility of bulb sizes.. from 2k up to 4k's.

Just remember that with the smaller bulbs, the 1k to 3k 'suitcase' switcher rectifer would be the way to go..for both houses.. ..

Simplex XL would be the way to go then..since you're deciding on a STRONG setup..

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
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 - posted 05-10-2006 01:01 AM      Profile for Sean McKinnon   Author's Homepage   Email Sean McKinnon   Send New Private Message       Edit/Delete Post 
AFAIK... The screen size is what matters when figuring lamp size... the throw really does not matter. I prefer going with a bigger lamp because the more your able to defocus the lamp the more even the light will be on the screen and the cooler the film gate/trap will stay. I personally prefer a bright image and really like light readings of 18-20 fl in scope which is "too bright" according to SMPTE standard and may bother some people. also if you have no choice but use a smaller lamp I think it is better to have a less bright picture with an even field of light that to force a reading of 16fl on center on scope by over focusing the lamp and causing a hot spot and dark sided/corners. If tou take the capentry analogy that you can cut a board too long u can always cut a little more off, but if yuo cut it too short to begin with you have to throw it away and start all over again you will understand why I prefer to spec up a lamp size.

Also I really like the SLC and the Super Lume-X, I prefer the Super Lume-X Because they look very sleek on a pedastal where the SLC (or SLH rather) is rather boxy looking, and while I like the electric focusing scheme I prefer the Super Lume-X design where you actually move the cathode end of the lamp by hand and you can adjust vertically and horizantly simultaneously.

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
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 - posted 05-10-2006 01:11 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Sorry, Sean - you do need the throw length and the width of the scope screen to get the correct amount of lumens - to get the preferred 12 to 16fl screen brilliance from the bulb.

..and his measurements of the width of the scope screen against his throw, which are pretty good sized measurements against the seating capacity per each cinema, do rectify the recommended kw of the bulbs needed to fulfill the necessary brightness.

In short, he would have a very good presentation on those screens.

-Monte

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Phil Blake
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From: esperance western australia
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 - posted 05-10-2006 01:21 AM      Profile for Phil Blake   Author's Homepage   Email Phil Blake   Send New Private Message       Edit/Delete Post 
Andrew your cinema 1 measurement are almost identical to my cinema one which is lit by a Cinemeccanica consol with 3K xenon , the light is perfect.

youe cinema 2 is slightly larger than my cinema 2 which is also lit by a Cinemeccanica consol with a 2k xenon , this is borderline , I would go with 2.5K

Phil

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Steve Guttag
We forgot the crackers Gromit!!!

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From: Annapolis, MD
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 - posted 05-10-2006 06:56 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
quote: Monte L Fullmer
Sorry, Sean - you do need the throw length and the width of the scope screen
Monte, where do you get this crap? Do you just make things up? The throw has zero, notta, nill to do with the size of the xenon lamp needed. At best, some may argue that when one is at extreme long focal lengths, the light will be reduced by the focal length interraction with the exit diameter of the lens barrel (over 140mm).

As for the lamp size...Cinema 1 will be in the 3K range (Super-80 or Ultra-80...Ultra-80 has better cooling). Cinema 2 will be in the 1.6K range and a Super Lume-X (it is actually a more efficient reflector than the Super-80/Ultra-80).

As for defocusing the lamp...there really is just one proper focus point to get the light right. Yes you can defocus a lamp but it really is not the right way to get the best image or least heat. Defocusing the lens might eliminate seeing scratches too but again, it isn't the correct solution. Size the lamp properly, align the lamphouse perfectly and adjust the lamp properly. You will end up with a non-hotspotting image and coolest running gate because most of the light will be going through the film and not splattering on the back of the trap.

BTW, SMPTE is 16fL +/- 2 fL for review rooms and +/- 4fL for cinemas so enjoy your 20fL images all you want.

As for controlling the light using a larger lamp, you can also look into Schneider's new Cinelux Premier lenses...they have an adjustable iris from f/1.7 to f/4.0. This way, if you do choose to over lamp and block some light, you can pick up improved depth of focus for your efforts.

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Andrew McCrea
Jedi Master Film Handler

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From: Winnipeg, Manitoba, Canada
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 - posted 05-10-2006 08:41 AM      Profile for Andrew McCrea   Author's Homepage   Email Andrew McCrea   Send New Private Message       Edit/Delete Post 
Oh, I thought throw had everything to do with xenon wattage. I thought that if you had a really wide screen, with a really short throw, you'd have to increase the wattage.

I was told one of our older picture palaces had a screen of 40'x17' with a throw of 102' and a xenon of 3kw.

So, with your suggestions and the decision to use two Super 80s:
#1: 3kw
#2: 2kw

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John Pytlak
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From: Rochester, NY 14650-1922
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 - posted 05-10-2006 09:54 AM      Profile for John Pytlak   Author's Homepage   Email John Pytlak   Send New Private Message       Edit/Delete Post 
As Steve notes, the distance from the projector to the screen (throw) has NOTHING to do with the screen luminance for a given lamp. It is the AREA of the projectable image, and the AREA of the image on the screen, along with the type of shutter, the screen gain, and any losses due to an inefficient lens or port glass without anti-reflection coatings.

About the only way a really long throw can cut light level is when you are restricted to a longer focal length lens with less efficiency, or are projecting through fog, smoke or rain.

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Louis Bornwasser
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From: prospect ky usa
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 - posted 05-10-2006 11:36 AM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
BTW: The 2500 watt super lumex and the 3000 watt super 80 have the same lumens output. Strong sent a letter out in the early 80's so stating. If you want more light go up to 4k.

As far as the throw, it does not matter in a technical sense. What does matter is that a short throw with a very wide picture will leave you with the appearance that it is bright in the middle and darker in the corners. This is a function of the angle of reflection from the screen. Light in the middle comes straight back and light on the top, bottom, & sides reflects outward. This is proved easily with white light and a light meter. The difficulty is that you can prove that the screen is evenly illuminated by the meter; it sure doesn't look that way from any particular seat. Louis

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Monte L Fullmer
Film God

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From: Nampa, Idaho, USA
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 - posted 05-10-2006 12:26 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
(Sorry, Steve - been listening to some "tekkies" who knew it all at one time long ago..and this one kinda stuck until now..)

Okey, how does one calculate how big a bulb should be for the size of screen and distance to get the correct brightness then?

Is there a computer program, simple math solution, et.al. , so that in the future when one wants to constuct a theatre, either home or public, that he can then take this simple program and come up with the answer for himself.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 05-10-2006 01:00 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
There are rules of thumb on that one. The basic one is to take the screen height of your least efficent format (typcially 1.85), square that and then multiply by 12 if it is a good lamp system and appoximately 50% shutter with decent lenses or go with 13 if you are using less efficient reflectors.

So for a 10-foot tall screen with a Super Lume-X and decent lenses you have 12*10^2 or 1200-watts for a matte white screen.

As John mentioned, there are other factors that can improve or take away from the light like the port, the actual screen gain and so forth. Even the lamp package can affect the light throughput (not just output). The size of the arc and the size of the aperture have a relationship not unlike the size of a slit lens versus the HF response. Thus you find that short-arc lamps are more efficient (typically have an "HS" suffix in their name).

If you find that you have moved to the "larger" lamps say 3K and up, then you find that you should use 13 as the multiplier so for a 15' tall picture it would 13*15^2 or 2925-watts is a good target point for a typical lamphouse/console system.

As for Louis' observations on hot-spotting on short throws...there are several reasons for this...first, the screens are probably not matte-white, despite manufactur's names. Unless you are using a Stewart Snomatte 100, the screen probably has a non-matte characteristic. This will give you a hot-spot.

The lens design is another area. Schneider lenses tend to hotspot (and make the light more blue) than ISCOs. So if you combine a typical cinema screen with a Schneider lens you will tend to see a screen with the image brighter in the middle. An ISCO Ultra-Star PLUS lens (red one) will not have anywhere near the amount of hot spotting. The newer Schneider Cinelux Premier lenses are said to also provide a more even light as compared to earlier designs.

Short throws accentuate this sort of uneven illumination, as Louis notes, due to the angle the light takes to the screen and the mirror like qualities of many screens. Curving a screen properly will mitigate this but that can bring about other artifacts as discussed in other threads.

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Sean McKinnon
Phenomenal Film Handler

Posts: 1712
From: Peabody Massachusetts
Registered: Sep 2000


 - posted 05-10-2006 09:34 PM      Profile for Sean McKinnon   Author's Homepage   Email Sean McKinnon   Send New Private Message       Edit/Delete Post 
Thank you Steve and John for backing me up... I used to think that the throw mattered too until I became a tech and learned a little more clearly how it all worked.

All I meant was that if you had a choice of 2 lamp sizes one bieng a little too small and the other a little too large that you should go with the slightly larger one rather than overfocus the smaller lamp and have dark corners and hot spotting. Basically that if the math calls for 1.6k lamp which afaik no manufacturer makes go with the 2k instead of with a 1.5

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