Recently we've encountered cracked inner lenses in some old Altman 360Q 6x9s. It might be a problem of too fast warm-up (the theatre is cold in the winter and some less-than-experienced technicians may have slammed them to full without pre-heat.) It might also be due to slightly hotter lamps: the units have been upgraded from 500w EHDs to 575w FLK/LLs. Any ideas about possible cause and remedy? Thanks!
Conventional Fixtures Cracked lenses in 360Qs
- Thread starterPMWest
- Start date
Did you re-align after the lamp change ?.
The FLK has a slightly different lighted center length (if memory serves) and might be causing a hot spot in the lens, aggravated by the cold.
It happens. The 360Q 6x9 lens is rather thick and is a rather cheap lens that is proned to defects. Over time heating and cooling, movement, and whatever else can cause the lens to crack. Sometimes the crack can be seen in the quality of the light produced, sometimes not. A 575w lamp is not going to really cause this, most people run these units at 750w. New lenses really are not cheap: Altman Lens, 6x9 Plano Convex, for 360/360Q
What???
I sold 6 lenses for $50 total earlier this month.
SteveB, yes we did a bench focus after the lamp change, but it was a while ago. Maybe worth revisiting the units. And, avkid, this isn't an epidemic: 3 units out of 36. Just trying to prevent it from spreading further.
Les
Well-Known Member
.Don't think I have ever seen a cracked inner lens - even on the green ones. Worked on many more than a hundred or two amongst brands and especially the 360 series.
Above very good concepts in cause as with what you are cleaning them with and if chemical, what did you remove it with? Believe on my part a little less weight on age of lens though bad lot number is certainly possible and valid especially over time to see. FLK lamp isn't hard usage but bad bench focus not done certainly would be bad.
Final note, while I love dish washering my lenses (wife not much a fan of it in a as' opposed to what washed question), I have wound up with broken lenses if too thick and in the bottom shelf of the dish washer on high heat. Possible that especially if at a school that if sent thru an industrial dish washer for the best cleaning, or if in the bottom shelf of a standard dish washer, that a fault developed which when heated by a lamp cracked?
Above very good concepts in cause as with what you are cleaning them with and if chemical, what did you remove it with? Believe on my part a little less weight on age of lens though bad lot number is certainly possible and valid especially over time to see. FLK lamp isn't hard usage but bad bench focus not done certainly would be bad.
Final note, while I love dish washering my lenses (wife not much a fan of it in a as' opposed to what washed question), I have wound up with broken lenses if too thick and in the bottom shelf of the dish washer on high heat. Possible that especially if at a school that if sent thru an industrial dish washer for the best cleaning, or if in the bottom shelf of a standard dish washer, that a fault developed which when heated by a lamp cracked?
Les
Well-Known Member
I've seen a few cracked 6x9 inner lenses. One was just an old 6x9 360Q at a high school -- could have been anything that caused it.
One other time, it happened to one of my own stage lights. A friend needed some extra ellipsoidals for backlights in a studio space, and we had them powered up while doing a rough focus. Then I heard a crack. I pretty much knew what it was, but checked anyway. Yep, one of my inner 6x9 lenses cracked in a Y formation --- 3 separate pieces. I'm not sure what caused it; the lenses had been cleaned a few weeks prior, but only with water and it was done by hand. Now, the lamp may have needed a bench focus but I'm not for sure (the lamp was a 575w GLA type). I do remember one of the lenses having a non-removable brown stain on the flat side, almost like something had dripped on it, however, nothing I would do could get this stain out. It may have been the same lens, and it may have caused a hot spot. All I know is that I wasn't thrilled about replacing the lens since I didn't have any spares (hence my using the lens with the spot on it).
Now a more perplexing situation, perhaps proving that it can seemingly happen at random. A year or two ago, I was doing a lighting check-up at an elementary school in my town. FOH is 5 brown 360Q's - again 6x9, year 1987 models. Noticed that one had its rear lens cracked in half. All lights are the same, and all are used at the same intensity for the same amount of hours (they pretty much either have all the front lights on, or all off as they are only divided in to two channels). None of the other fixtures showed problems. I can say that these fixtures don't get cleaned other than surface dusting. I didn't note much other than a light dust on the exteriors (nothing that looked like lint, which would indicate zero cleaning efforts), but I'm sure the optics have at least a little dusty patina (also noted one fixture with a single cobweb string extending from one side of the colorframe to the other). I very highly doubt these fixtures have ever been taken down, much less cleaned out. They still use the same gels as they did when I was a student there... LONG ago. Oddly, no burn through or fading, but that could be because of the fact that these fixtures are light usage and the gels are high transmission no color pink/no color blue. They see in a year what most high school and theatre fixtures see in a week.
I also ordered an older light from eBay (another 6x9) that arrived with a cracked inner lens. I've seen this (more rarely) on 6x12's as well. I think it has a lot to do with the short distance between the lamp and the lens, as well as the thickness of the lens and its reduced capability of heat dissipation (due to the thickness). Bumping a light around could crack a lens but I'd call it doubtful. I've accidentally dropped lenses 6x9 on to bare concrete. They will chip like heck, but cracking in half usually takes a solid blow to the lens' center. Cracked outer lenses may indicate a blunt force, but I never really see that happen. A FEL 1000 is a sure way to crack 6x9 optics.
One other time, it happened to one of my own stage lights. A friend needed some extra ellipsoidals for backlights in a studio space, and we had them powered up while doing a rough focus. Then I heard a crack. I pretty much knew what it was, but checked anyway. Yep, one of my inner 6x9 lenses cracked in a Y formation --- 3 separate pieces. I'm not sure what caused it; the lenses had been cleaned a few weeks prior, but only with water and it was done by hand. Now, the lamp may have needed a bench focus but I'm not for sure (the lamp was a 575w GLA type). I do remember one of the lenses having a non-removable brown stain on the flat side, almost like something had dripped on it, however, nothing I would do could get this stain out. It may have been the same lens, and it may have caused a hot spot. All I know is that I wasn't thrilled about replacing the lens since I didn't have any spares (hence my using the lens with the spot on it).
Now a more perplexing situation, perhaps proving that it can seemingly happen at random. A year or two ago, I was doing a lighting check-up at an elementary school in my town. FOH is 5 brown 360Q's - again 6x9, year 1987 models. Noticed that one had its rear lens cracked in half. All lights are the same, and all are used at the same intensity for the same amount of hours (they pretty much either have all the front lights on, or all off as they are only divided in to two channels). None of the other fixtures showed problems. I can say that these fixtures don't get cleaned other than surface dusting. I didn't note much other than a light dust on the exteriors (nothing that looked like lint, which would indicate zero cleaning efforts), but I'm sure the optics have at least a little dusty patina (also noted one fixture with a single cobweb string extending from one side of the colorframe to the other). I very highly doubt these fixtures have ever been taken down, much less cleaned out. They still use the same gels as they did when I was a student there... LONG ago. Oddly, no burn through or fading, but that could be because of the fact that these fixtures are light usage and the gels are high transmission no color pink/no color blue. They see in a year what most high school and theatre fixtures see in a week.
I also ordered an older light from eBay (another 6x9) that arrived with a cracked inner lens. I've seen this (more rarely) on 6x12's as well. I think it has a lot to do with the short distance between the lamp and the lens, as well as the thickness of the lens and its reduced capability of heat dissipation (due to the thickness). Bumping a light around could crack a lens but I'd call it doubtful. I've accidentally dropped lenses 6x9 on to bare concrete. They will chip like heck, but cracking in half usually takes a solid blow to the lens' center. Cracked outer lenses may indicate a blunt force, but I never really see that happen. A FEL 1000 is a sure way to crack 6x9 optics.
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