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Topic: Projected Image of Gas from Xenon Bulb
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Paul Konen
Jedi Master Film Handler
Posts: 981
From: Frisco, TX. (North of Dallas)
Registered: Jun 99
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posted 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
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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!
Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999
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posted 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
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Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
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posted 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!
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