This is topic Broken Lens in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Christopher Duvall (Member # 284) on 12-31-2001, 02:36 AM:
My projectionist today called me up to the booth to report a small reflective distortion on the screen on my big house during the credits. My first thought was dirty lens or port glass, but after the movie dropped I inspected the lens and it had a spiderweb of cracks throughout. My question to the techers out there...Could heat from the bulb cause this? It is a 5k bulb running about 95% of its rated power and the projector is water cooled. The movie is Lord Of The Rings which means the lamp is shining through that lens for over 3 hours. We have been only open for a week and a half and I just have a hard time believing this could be the case. I have ran Titanic on the same equipment at another location and had no problems. From what I do know, the automation has been running OK as well so the bulb has not been shining through the lens without film present. Any insight would be helpful.
Posted by Aaron Sisemore (Member # 145) on 12-31-2001, 02:56 AM:
the only way that heat could have done that to a lens was if it was run wide open (lamp on dowser open and NO film in the gate) for a period of time. You say that there were no instances of running like this, so the next thing to consider is physical damage from dropping, hammering, etc. You also don;t specify if its the prime lens or the anamorphic attachment that is damaged.-Aaron
Posted by Christopher Duvall (Member # 284) on 12-31-2001, 03:39 AM:
Sorry, it was the prime. The anamorphic is fine.
Posted by Frank Angel (Member # 248) on 12-31-2001, 04:13 AM:
I came across this once before -- it wasn't a total spider kind of crack as yours, but two cracks that made arcs, like half circles, each starting at the barrel and curving out into toward the center of the lens and then back out to the barrel again. We determined the cause was a quick and deep drop in the ambient temperature in the booth -- this was a drive-in in Texas. The booth closed for the night and the area was hit a unusually frigid cold spell overnight, down to near freezing and remained that way for the rest of the week. This theatre would close during the winter and because the winters were usually mild anyway, so there was no real room heating system, just a small area heater in one corner. So when the operator came in, the booth was really cold. The space heater wasn't much help.
We surmized that it was the sever temperature change that was the culprit -- starting the next night show after the equipment has been sitting in near freezing temps all day, then the dowser is opened and that rush of heat hits the lens barrel and elements -- bingo, cracked lens. By the time the second reel (change-over/6000ft reels) was ready to roll, the room and the lamphouse had already been on long enough to raise the temperature so that shock stress didn't happen to the other lens. We also noticed that the lens grip was tightened VERY tightly (those insecure projectionists needing to prove their manhood by tightening the lens lock so tight that you need a pipe wrench to loosen it -- you know who you are); this possibly putting extra stress on the lens via the barrel. When the heat hit it, the barrel expanded quickly and the lens cracked.
It is only a theory, but it was the best we could come up since the temperature change was the only odd element that was different -- everything had been running flawlessly for weeks before.
cracked with and it seemed to make sense.
Posted by John Walsh (Member # 168) on 12-31-2001, 09:02 AM:
If it is a single-lens holder, it could have been dropped or accidently banged into something. If it is in a lens turret, it may have cracked because someone allowed light to shine through without any film or as Frank said, abrupt changes in temperature (although I have only heard of this happening once before and it was not verified) It could be either damage during shipping or installing no one noticed.I hate to say this, but my real guess is (since you just opened) the tech left the dowser open too long while filing aperture plates. 5k watts is pretty hot. Water cooling only helps keep the projector head cool (which helps the film itself a little) but does nothing for the lens. Do you have glass heat filters installed(?), which will help. The pattern of cracks ("spiderweb") is an indication of what caused the damage; you could give the lens manufacturer a call (they may even still honor the warrantee.)
Was the crack on one of the outside elements? If you have turrets, check to see if it is possible to hit the lens when opening or closing the turret. On our Simplex projectors (with two-lens turrets and "swinging-hinged at the top" gates) if someone leaves the gate open and either opens or closes the turret -or- rotates the turret, it will hit the lens.
As a side note (and in my own opinion) there are not enough good techs to go around. A service company usually only has one or two good tech on staff, because there's not enough work to hire and keep more. Also, the sooner the building nears completion, the faster the work goes. If it is a larger place, especially a 16-plex or bigger, the sevice company must hire temporary help, sometimes "less than good" help, to keep up the pace.
At two of our theater installations (in a row) we had to do this, and at both of them we did have cracked lenses, which no one noticed until a few days after opening.
Posted by Randy Stankey (Member # 64) on 12-31-2001, 09:27 AM:
In a place where I used to work, somebody was screening a movie but had the projector running manually. When the film tailed out the projector kept running and the lamp was shining through an open gate. The projector was left running for a long time like that and the lens was fried pretty badly.Since you say the place is pretty new, I'm going to bet that some raw recruit did something like that and fried the lens. With a 5 KW lamp, the lens will be damaged in pretty short order.
The only real solution is to replace the lens. In the mean time you can get your most important movie up and running by swapping lenses around. Look through your projector spec sheets and find one with the same size lens. (Focal length & diameter) Put the better lens in the house that has the best movie. If you can order the lens by overnight shipping or you can otherwise get a lens on short notice just put the house with the crummiest lens/movie out of commission for a day. Otherwise you are going to have to run a movie on that damaged lens.
If it was MY decision I'd put the house down until the new lens can be installed. You're going to have to be one house down for the New Year's rush but, IMHO, that's the penalty that has to be paid when people don't pay attention to what they are doing. Personally, I'd rather be one house down than subject customers to crappy presentation because of a fried lens.
Posted by Mark Gulbrandsen (Member # 72) on 12-31-2001, 09:35 AM:
Like Aaron said, if the dowser was left open with the lamp on it can happen. If for some reason the automation doesn't shut the show down at the end,perhaps it was running manually and the operator forget about it, this can also happen, especially with larger than 2kw lamps.
Now the good news....If it is a Schneider or Isco lens it can be repaired. Just get it in to your dealer and borrow a lens out of another booth, or see if he can get you a loaner.
Mark @ GTS
Posted by Gordon McLeod (Member # 33) on 12-31-2001, 12:32 PM:
I have also seen bad bulb focus create a hotspot on the back element that has cracked them while the film is running. This was with a very short focus lens that has its back element very close to the film plane
Posted by Stefan Scholz (Member # 147) on 12-31-2001, 02:34 PM:
It's not only 5kW to kill a lens. We've been using a 1000W Italien tin mirror hotlight projector for a summer engagement, and just by trying to adjust the lamp, the rear element crackeled due to heat absorption. There was one crack, and mgmt decided to keep the lens, as "barely invisible on screen" (for an economist).
This type of projector, you could not stick your finger into the gate, severe burn were following, with my Kinotone lamphouses using Balzers style coldlight mirrors and Balzers heat filter plates you could stick your finger into the gate for quite some time running 140A before they get hot, assuming this is the visible radiation absorbed. The Milano reflector reflected and focused just 1 thing: heat.
Posted by Mark Gulbrandsen (Member # 72) on 12-31-2001, 03:55 PM:
Stefan said "The Milano reflector reflected and focused just 1 thing: heat." Perhaps more evidence as to why the theatre in Cinema Paradiso burnt down..... 
MArk @ GTS
Posted by Scott Norwood (Member # 30) on 12-31-2001, 09:53 PM:
I've always been paranoid about lenses cracking due to excessive heat, but I know of at least two instances where projectors were left running for about twelve hours (!) with 2kw xenon lamps lit, changeovers and hand dowsers open, yet where the lenses were undamaged. In both cases, the film had been running on a platter and apparently brainwrapped toward the end and melted. Thus, the automation end cue was never detected and no one bothered to shut down the booth (or even check the auditoria) before closing the building for the night. I don't know the whole story, but apparently the old B&L lenses survived and are still being used.... Weird.
Posted by Christopher Duvall (Member # 284) on 01-01-2002, 04:36 AM:
My fears have been confirmed. I have inspected the lens closer and I found a nick on the edge that could only indicate that the lens was dropped. I am beyond ticked 
right now and more so because the guys in the booth seem to not know what happened. If someone screwed up, I would be mad but understanding because I know 
happens. However, I think I am going to rip someone's head off because I know somebody knows what has happened but will not come forward. Grrr!
Posted by Steve Guttag (Member # 268) on 01-01-2002, 10:10 AM:
Christopher,Do you use turrets or single lens? With turrets, about the only way the operators could have contributed to nicking the lens is on some projectors (eg Simplex PR-2000) the pad rollers and intermittent shoe can be in the lens' path when the turret rotates if they are open.
Steve
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"Old projectionists never die, they just changeover!"
Posted by Christopher Duvall (Member # 284) on 01-01-2002, 02:59 PM:
It is the older model Simplex with the motorized turret. It opens and closes on its own. The operator cannot open or close it manually. They just have to make sure the gate is closed. It looks like it was removed from the turret by the way it was dinged. They should have known better anyway, it was an anamorphic lens and that should not be removed unless absolutely needed. Our tech is the only one besides myself that can align the anamorphic and adjust throw of all lenses. These guys have not been trained on this and should not be pulling lenses out of turrets. I will find out what happened.
Posted by Christopher Duvall (Member # 284) on 01-14-2002, 01:53 AM:
OK...I was wrong about the abused lens. I have had the lens replaced this week and yet again it cracked. The scuff mark I saw before had been there for years from what I understand. I truly believe it was the heat this time. I am going to refocus the bulb and drop the amps a little. I just need to check the light output afterwards to be sure I don't drop below 16fl. Is there any other suggestions that may help reduce the chance of cracking another lens?
Posted by Steve Guttag (Member # 268) on 01-14-2002, 09:20 AM:
Proper lamp alignment is critical. Also, with a 5K lamp, I hope you are using a heat filter on your lamphouse!Steve
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"Old projectionists never die, they just changeover!"
Posted by Randy Stankey (Member # 64) on 01-14-2002, 12:12 PM:
The way I feel about it, I'd rather have the lamp focused so that it's too dim than too hot. You can always "bump it up" if you need to but if the lamp is too hot you can do damage before you even have a chance to correct the problem.How I would do it is to take the lens out and focus it the way it should be, but then back off just a hair bit. Then I'd cut the black credits off an old trailer or something, make a loop out of it and run that for a while. During that time I'd check it every few minutes. If the lens and/or gate is getting too hot I'd back off a bit more. Also remember that the black film will start to get hot after a few loops through the projector. If the black film can take repeated loops without burning or buckling it ought to be good enough for a "go show". Let it run for a few more minutes and check it again. I'd repeat the check/adjust procedure until I was comfortable with it.
Whenever I focus a lamphouse (putting in a new lamp or making repairs) I always baby sit it for the first show to make sure nothing bad is happening. Every time I have had film burned or had lens damaged from heat it was because somebody did an adjustment and didn't do any testing or checking before they started a "go show".
Posted by John Pytlak (Member # 331) on 01-16-2002, 09:12 AM:
Here are links to some articles on heat damage:
http://www.kodak.com/country/US/en/motion/newsletters/reel/fall97/pytlak.shtml
http://www.kodak.com/country/US/en/motion/newsletters/reel/winter97/projection.shtml
http://www.kodak.com/country/US/en/motion/screencheck/evaluation.shtml
http://www.kodak.com/country/US/en/motion/newsletters/reel/spring98/pointers.shtml ------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Ben Stephenson (Member # 741) on 01-22-2002, 05:48 PM:
At the moment i have a cracked scope lense in the bigest 35mm screen in Europe and it still looks ok but when the lense was fine in still was imposable to focus !
Posted by John Pytlak (Member # 331) on 01-22-2002, 09:34 PM:
Ben said: "At the moment i have a cracked scope lense in the bigest 35mm screen in Europe and it still looks ok but when the lense was fine in still was imposable to focus !"Even if the crack is on a lens element that isn't imaged, it's very likely that it is a "contrast killer":
http://www.kodak.com/country/US/en/motion/newsletters/reel/december99/pytlak.shtml
As far as focusing difficulty, does your prime lens have a really short focal length? Or is there some problem with the anamorphic attachment?
------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Ben Stephenson (Member # 741) on 01-23-2002, 12:59 PM:
prime lens has a really short focal length and the anamorphic attachment is fine, just ordered and new lense after i just got the wrong replacment !