This is topic heat waves? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Josh Jones (Member # 447) on 03-10-2002, 10:04 PM:
I noticed something else when I was at "We were soldiers" today. at the top of the screen during the movie ther were curls of distortion, only noticeable in light areas of the picture which were darker than the surrounding white image. is that the hot air around the bulb distorting the light in the lamphouse or what? I also saw it during the prescreen ads and also in another house at the same theater. Anyone know what this is?Josh
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"Film is made of silver, video is made of rust"
'nuf said
Posted by Darryl Spicer (Member # 711) on 03-10-2002, 10:13 PM:
Well you sort of answered your question with the topic header. It is heat waves but from the hvac system. The waves of heat are refracting the light beam and is most apparent in bright scenes. This disapears once the room tempreture increases.
Posted by Paul G. Thompson (Member # 655) on 03-10-2002, 10:16 PM:
I agree with Darryl. I have seen that phenomena many times.
Posted by Josh Jones (Member # 447) on 03-10-2002, 10:26 PM:
Thanks for the info guys 
JJ
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"Film is made of silver, video is made of rust"
'nuf said
Posted by Mark Gulbrandsen (Member # 72) on 03-10-2002, 10:32 PM:
Josh,
Thats exactly what it is. The heat waves from the ceiing mounted vents that shoot air downward into the cone of light traveling to the screen. Its definately not the plasma inside the bulb or anything like that. I remember once an engineer fomr HAnovia telling me that the actual plasma itself has never been observed in an operating xenon lamp.Paul, Please put that weenie down will ya. There's weenie goop running out from all over my monitor screen! All it does is smear around, can't clean it off!
Mark @ GTS
Posted by Paul G. Thompson (Member # 655) on 03-10-2002, 10:37 PM:
Mark, It does kind of have a 3-D effect, doesn't it? I kind of got the idea from Joe Redifer's finger. 
Posted by Steve Kraus (Member # 476) on 03-11-2002, 12:07 AM:
Mark, if there is, um, goop on your monitor it must be on *your* side of the glass. I can only wonder what sites you've been visiting!
Posted by Jerry Chase (Member # 660) on 03-11-2002, 12:11 AM:
I'm gonna disagree with youse guys. I had this exact problem in the Strong X-15 vertical lamp lamphouses. They used two reflectors, with the front one being solid metal. I was always getting heat waves, whether the HVAC was on in heat, air conditioning, or turned off entirely. I put up with those damn things for years.This isn't plasma, which would theoretically only be within the arc itself, it is the hot gases "boiling" and transferring heat from the arc to the envelope.
I've never seen this problem be as noticable with horizontal lamps or deep dish reflectors. The double reflector system somehow accentuates the visibility, perhaps because the light is shining through the gas to the front reflector, then back through the gas again, all the way through before being caught by the rear reflector.
HVAC units can also cause problems, so I have no idea which problem Josh is seeing. The thing to ask would be whether the lamphouses have vertical lamps and double reflectors.
Paul, I hope you brought enough weenies for everyone.
Posted by Aaron Sisemore (Member # 145) on 03-11-2002, 12:44 AM:
This one has been the subject of many an argument... Here's mine.Unless someone can give me evidence to the contrary, it is impossible for the heat 'convections' either in the bulb itself or inside the lamphouse to show up clearly on the screen with the lens in, as neither of them are anywhere close to the focal point of the lens.
Which leads us to the next cause. EVERY time I have seen this phenomenon happen, the heaters were operating, and in nine out of ten cases there were HVAC registers within 5 feet from the screen. Turned off the heater, phenomenon went away. I have seen this happen to a lesser extent when A/C was operated in a warm auditorium as well, with similar curative actions (turning the system off)
Lamps I have observed this phenomenon occur with include:
CFS consoles
Christie horizontal lamps
Xetron XHC-35 and XH2000 horizontal lamps
Strong X-16, Super Lumex and Super 80
Peerless Magnarc (so much for the 'gases in the bulb' theory!)
My bottom line here: its the HVAC system!
-Aaron
Posted by Paul G. Thompson (Member # 655) on 03-11-2002, 12:47 AM:
Jerry, I have seen the heat waves you speak of while targeting Xenon lamps on the screen without a projection lense, but never observed it when the lense was in the projector. If Josh saw billowing clouds of heat waves at the top of the screen during the movie he was watching, I'll bet it was from the HVAC system. The North Dakotans are presently freezing their asses off, and the HVAC systems in the theaters are probably running at full capacity.
Posted by Darryl Spicer (Member # 711) on 03-11-2002, 01:15 AM:
I too have seen the heat waves that Jerry speaks of while targeting a xenon bulb without the lens in place. But as soon as you put that lens back in you no longer see the problem. In Joshes case it is the HVAC system.
Posted by Jerry Chase (Member # 660) on 03-11-2002, 01:28 AM:
Well... I can no longer provide the evidence, but a few years of standing at the port glass staring at the upper right corner of the screen waiting for changeovers (with lens in place) gave me plenty of time to curse these. I know what I saw. I don't see much point in belaboring it further. If it isn't there, you won't see it.Yes, if you remove the lens the movement can be very apparent.
Posted by Pete Naples (Member # 761) on 03-11-2002, 02:44 AM:
The Cameo in Edinburgh has suffered the 'waterfall effect' for as long as anyone can remember. Various experts told us it was gas convection in the bulb and/or lamphouse and there was little we could do. Changing from a Magnarc to a Super Lume-X made no difference. It looks really bad in there as the ventilation (extract, no AC) ducts are position dead on the centre line of the theatre, and when the fans aren't running, ie it's cold, then you get cold air falling down the vents from outside. These vents were installed a long time before anyone thought about electric dampers or such like. By trial and error I found that I could eliminate the effect by matching the speed of the enormous 3 phase extract fan (this thing is cast ally and is about the size of a small helicopter! Well ok I exagerate, but you get the idea, one fan pulls all the air from a 250 seat auditoreum). Must have looked kind of odd to anyone coming into the booth to find the projectionist looking out the port, adjusting the fan speed controller, looking out the port, adjusting the fan speed controller....
Posted by Wes Hughes (Member # 981) on 03-13-2002, 01:38 AM:
As Jerry said, I too have seen this at a now closed screening room style theatre I used to operate...It had Cinemecannica Zenith 1600 watt vertical lamphouses with auxillary reflectors. They always had a noticible "light swirl" on the screens. The rooms had radiant floor heating buried in the slab, and it happened exactly the same all year long.
Posted by Brian Hogan (Member # 940) on 03-13-2002, 03:31 AM:
YES! i too have seen the waves while focusing the bulb sans lens. at least we arent agreeing to disagree... yet
Posted by Jon Hudson (Member # 439) on 03-24-2002, 03:09 PM:
Well, it has been some time since I have been here. The problem that Josh is speaking of is from the bulbs, not so much the HVAC units. It is most noticable in our Kneisley consoles and lamphouses. Hard to figure, as everything in the booth is very well vented.
But we do also have 1 auditorium where the heat does affect the screen from time to time.
Agree or dis-agree, HVAC and bulbs are both to blame.
Posted by Aaron Sisemore (Member # 145) on 03-25-2002, 12:47 AM:
One more time... and another point to be considered for those of you that insist that the swirling 'waves' are an image of convections within the bulb or lamphouse:This phenomenon ALWAYS occurs at the TOP of the screen. If it were the 'bulb convections' (which in my previous post I claim is impossible (with the lens in) because they are nowhere close to the focal point of the lens) then they would occur at the bottom of the projected image as it would be inverted by the lens!!!
ITS THE HVAC, PEOPLE!!!
-Aaron
Posted by Jerry Chase (Member # 660) on 03-25-2002, 11:13 AM:
No. I don't feel like arguing the point though. Most lamps are horizontal now and it is not worth getting in a tizzy over. Someday (maybe) you'll run across a situation where you'll see it.My father was a staunch non-believer in UFOs until the summer of 1973 when he watched and photographed a pair of them do stunts that aircraft were incapable of.
Posted by Gordon McLeod (Member # 33) on 03-25-2002, 02:06 PM:
Actually I have seen the heat patern radiate out from the centre in verticle ORC consoles with the HVAC turned off
Posted by Paul G. Thompson (Member # 655) on 03-25-2002, 02:29 PM:
Jon, it was depends where it was seen from what part of the auditoruim. If the observer seen it from the rear of the auditorium, it was probably from the HVAC.
If the observer seen the heat waves while sitting close to the screen, and the HVAC vents are way behind him, then I will concede they may have been coming from the lamphouse.
Which was it?
Posted by Jon Hudson (Member # 439) on 03-25-2002, 04:51 PM:
Ok, this effect had bothered me a long time before Josh addressed it here, so I experimented. I turned off the HVAC units, fired up the lamp with no film, just lamp and lens, and no matter where you sat in the auditorium, you could see the "heat waves", hard to call them "heat waves" though, more like a fluctuation in the light around the center of the screen (not from the shutter either).The trouble is, that a person has to look REALLY HARD, as if they were looking for something wrong. I spent a lot of time observing the screen with just light on it, and thats just it, a person has to "spend a lot of time" looking and looking closely.
Of course, if you take the lens out, a person can see the "heat waves" with no problem.
And again with the HVAC units, after reading this yesterday, I had to go look at ALL of the auditroiums and we do have a few where this is a problem when the unit is heating.
So again, both HVAC and bulbs are the cause.
Maybe if Josh wants to help solve our HVAC "heat wave" problem in those specific auditoriums, he can come in and help move the vents.
I actually came in here searching for problems relating to DTS matching some trouble that we are having. I loath DTS so much that I don't even want to explain it all. I just want to sift through the DTS posts. One problem fixed however, SCSI CD-ROM drives work just fine.
Posted by Randy Stankey (Member # 64) on 03-25-2002, 05:17 PM:
I know WHAT causes this, "Schlieren Effect"... it is pockets or swirls of air at diffeent densities which refract light differently.It can be seen when looking at a flame, say from a campfire. You can also see it in the ocean when swimming under water, near the surface during a rain storm. (The fresh water from the rain intermixing with the salt water.)
I have seen it in a CFS console many times and have always assumed that it was from the heat of the lamp. I, too, have never seen it in a Christie, or any other horizontal-style lamphouse.
I don't see why it couldn't be from the HVAC system, blowing in warmer or cooler air, though. It could even be caused by the heat rising off some other piece of equipment in the booth, such as a hot projector motor.
Now that I read this discussion, I'm not so sure as I once was as to the source. I can, however, propose a way to find out the source... a fan. When somebody sees the swirls from the schlieren effect, it should be an easy matter to take a piece of cardboard and wave it in front of the lens like a fan. If it causes the swirls to change or disappear you have found the source. Keep fanning in different places until the source is found. If you have tried all other places, inside the booth and outside then the last place would be inside the lamphouse. In this case I might figure out a way to place a small electric (battery powered ?) fan/blower inside the lamphouse and strike it back up. Again, if the swirls disappear or change pattern you have found your source.
Again, I don't dispute that it MIGHT be from the HVAC system blowing air into the auditorium but I have always though it was caused by heat build up inside the lamphouse. On the CFS, there is a diagonal cold mirror that can act like a heat trap and cause a layer of warmer air to rise up the incline, especially if yours is the type/vintage that doesn't have the electric blower on the back of the cold mirror. (Or if the fan gives out.)
Posted by Barry Hans (Member # 477) on 03-25-2002, 06:02 PM:
Jon, you did'nt have the light running through the lens for any more than a few seconds at a time I hope. It could be real bad for the lens to just let light blast through there. Now this is going to be a dumb question but is there any oil on or in the lens? Are the ports optical glass? I don't know if the glass would make any difference, just a question.
As for the DTS what does Craig say about it?
Posted by Paul G. Thompson (Member # 655) on 03-25-2002, 06:13 PM:
Jon, is there a chance you are pushing your xenon power supplies too hard? What size lamps are you using, and what is the model no. of your power supplies? I have seen what you described, and when I throttled down the power supplies a little, this problem went away.How many hours do you have on that specific lamp? Is it in just one house, or all 14? Is there a chance a blower in the lamp is running off-balance and shaking the crap out of your lamp? Is there a chance of a harmonmic vibration developing in your lamp? Is it occuring with on both flat and scope lense?
What you see on the screen with the lense in the projector does not sound like "heat waves" to me.....
And, yes, be careful about sending raw light through your lense. It could burn them up. A few seconds at a time, than wait a minute or two and let the lense cool down before you hit it again.
Posted by Jon Hudson (Member # 439) on 03-25-2002, 07:04 PM:
Hey Barry, how you doing?
As far as the DTS, I talked to the Big A about it last week and I have some ideas to try. I was just looking for anything similar.
Posted by Karen Hultgren (Member # 395) on 03-25-2002, 07:32 PM:
So, Jon Hudson, why do you "loath" DTS????????Karen at DTS
And as far as your DTS problems, all you need do is email me, I'd be happy to help. Don't be shy!
khultgren@dtsonline.com
Posted by Gordon McLeod (Member # 33) on 03-25-2002, 09:49 PM:
Jon If you wish to ask a question or make a comment on a product do so in a seperate post don't hide it. And don't make unsubstantiated staements bashing a product in a vague fashion
One thing that does tend to piss me off is people who will bash a product and not back it up. Ususally I find out later they are not following the manufactureres instructions end of rant
Posted by Paul G. Thompson (Member # 655) on 03-26-2002, 01:20 AM:
Jon, I think you are being a little unfair to DTS. All equipment has troubles from time to time, but I can assure you from past experience with DTS, they will bust their butts to assist you with any problem the equipment developes. Their technical support is among the best in the industry.
I have to totally agree with Gordon. Many problems I have seen are due to operator error in one way or another. Perhaps a training seminar could solve some of your problems.
Why don't you explain the problem, and let's find the solution. That is one thing Film-Tech is about!
Posted by Barry Hans (Member # 477) on 03-26-2002, 11:18 AM:
Gee you guys give Jon a break! I loath all kinds of stuff. I loath waking up in the morning! It does'nt mean life su*ks.If anyone looking for a digital system looks only at Jon's post and decides DTS is junk, I pity THAT fool. Maybe we need to adhere to politically correct statements when refering to projection equipment and our feelings towards it 
Posted by Karen Hultgren (Member # 395) on 03-27-2002, 12:04 PM:
Since I have not heard from Jon Hudson, there must not be any DTS problems.Karen at DTS
Posted by Paul G. Thompson (Member # 655) on 03-27-2002, 05:44 PM:
Karen, maybe he read the manual...
Posted by Karen Hultgren (Member # 395) on 03-28-2002, 07:14 PM:
Or, he could just be shy.I hope all of you feel free to send me an email or post a message if you need DTS help. We'll do our very best to keep you guys rolling trouble-free.
Karen at DTS
khultgren@dtsonline.com