This is topic Projected Image of Gas from Xenon Bulb in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Paul Konen (Member # 41) on 12-03-1999, 10:17 AM:
Have any of you seen the waves from the gas being projected on the screen.I was watching the DLP Toy Story 2 (yes, again. I really like it) and saw the rolling waves of gas from the bulb. They went away after a while.
I was just wondering if any of you saw this in everyday life or is there something going wrong with the bulb.
Thanks ALL.
Paul Konen
Posted by Gordon McLeod (Member # 33) on 12-03-1999, 10:48 AM:
It is very common problem less nortacble with a flickering shutter than in continous light source
Osram has never been able to explain it to me
Posted by Bruce McGee (Member # 131) on 12-03-1999, 10:55 AM:
I have an Eiki EX-2000 with a 300 watt xenon lamp. When the lamp is reaching the end of its life, besides getting dimmer, and blue-ish, I have noticed a swirling effect on the screen. Upon looking at the lamp thru a pair of welders goggles, I saw the arc jumping all around the electrodes. Is this something like what you are seeing?I use the Ushio lamps on this machine. I know of no where else to get this lamp other than Eiki. Their P/N is 5108. It is a UXL-350E-O.
To give you an idea how little this machine is used, I bought the 3rd replacement lamp nearly 6 years ago, and have not used it yet! The projector was bought used in 1984 for $250. The owner had no idea what she had. I did, though.
Does ORC or Christie, etc. have this little lamp available?
Posted by Michael Cunningham (Member # 210) on 12-03-1999, 07:50 PM:
I will sometimes, very rarely, see this while focusing a new bulb. It sort of looks like a shimmer / swirl on screen. When the projector is started, shutter turning, the effect all but disappears. Very strange!!-Mike
Posted by Aaron Sisemore (Member # 145) on 12-03-1999, 10:58 PM:
Well I have another explanation for this little phenomenon- About 2 years ago I had just finished an installation on a 3plex and I was in the largest auditorium running the Jiffy test film and several other things while in the auditorium, and in the very bright portions of the films you could see the aforementioned 'heat waves' swirling about the image, mostly at the top of the screen. The DM saw this and wondered if the lamp cooling was insufficient as the heat from the lamp was showing up on the screen... Well after some investigating and trial and erroro experimenting, I had discovered that the cause of these swirly shadows n the screen was caused by heat- Not from the bulb or lamphouse, but it was heat coming from the HVAC registers in the ceiling, there were three of them all lined up in the very fromt of the theatre about 5' from the screen. Nobody believe me until I threaded up a piece of RP40, struck the lamp let it rip... 'heat waves' all over the place.... (the heater was operating in the auditorium at the time). I then asked the manager to turn the heater off, and voila! within 45 seconds the swirly shadow effect disappeared! I then told the manager to turn the heat back on, and bingo! the swirlies reappeared!! It cannot be the bulb, or even the heat inside the lamphouse as neither of these would ever focus themselves at the same time as the image on the film....
Try it, see if there is a connection.... I am sure you have this problem all the time during the fall/winter months, and never during the summer when the A/C is running 
Aaron
Posted by Aaron Sisemore (Member # 145) on 12-03-1999, 11:01 PM:
Or: are Paul and Gordon referring to arc unsteadiness?-Aaron
Posted by Randy Stankey (Member # 64) on 12-04-1999, 12:36 PM:
It's called schlieren.It comes from density variations in the air that refract the light, making a smoke-like effect on the screen.
I have CFS lamphouses and they are FAMOUS for it. They are so bad that you can see it on the screen in the brighter scenes.
If everyting else on you machine is in working order (Blowers 'n' stuff) and nothing's overheating it won't hurt anything.
It can be pretty distressing the first time you see it. I know I was freaked the first time! I ran up to the booth and spent about 1/2 hour just going over everything. Finally I asked our tech. & he explained it to me and I did some 'looking-up'.
Essentially, I would say, that your 'eye' is getting 'sharper'. I know mine has since I started hanging out here at Film-Tech!
Posted by Gordon McLeod (Member # 33) on 12-04-1999, 02:40 PM:
No I was not reffering to arc unstability but the swirling effect. I once asked a senior engineer from OSRAM in germany about it and he said they will sometimes do that what causes it he didn't know but said live with it
It is even abigger problem with followspots that are projecting pure contiuous white light
Posted by Tim Reed (Member # 137) on 12-05-1999, 09:13 PM:
It is from heat in the auditorium from the HVAC. This threw me for a loop for the longest time. After I noticed it was only occuring in the winter... bingo!That's definitely what it is.