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Author Topic: How Hot Should Lenses Get? Ian Bailey Master Film Handler Posts: 317 From: Nambucca Heads, Australia Registered: Jun 2003 posted 03-04-2005 05:31 PM                     After recently "cooking" a scope backing lens(which was secondhand and not sure really what condition it was in internally-apart from no obvious scratches etc)I am very conscious now whenever I adjust a Xenon.But I am still unsure how warm a lens should get with a "perfectly" adjusted lamphouse. I am a bit confused as my three projector/lamphouses all seem to act a bit differently. CINEMA 1:Simplex 1050/TU2000 turret/SuperLume-x/Ushio Xenon Great light on the screen,lenses almost cool to touch after running for hours. CINEMA 2:Simplex1050/TU2000 turret/Super Lume-X/Osram Xenon Good light on the screen,lenses warm to touch but very sensitive to Xenon adjustment.This was where I cooked the lens! CINEMA 3:Simplex PR1014/Kelmar Turret,Gate,Trap/Lume-X/Osram Xenon Poor light on the screen.Lenses get quite hot if Xenon is adjusted for maximum light on the screen and are warm if Xenon is defocussed.This cinema would have the warmest lenses usually.  |  IP: Logged Robert John Jeromson Master Film Handler Posts: 264 From: Auckland, New Zealand Registered: Jul 2004 posted 03-04-2005 06:16 PM                     Do you use any kind of heat filtering in the lamp house?  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 03-04-2005 07:40 PM                     Ian, just wondering if you use a meter to adjust the lamps. Also, with any of the lamphouses, are there any hot spots or is the light pretty flat.  |  IP: Logged Ian Bailey Master Film Handler Posts: 317 From: Nambucca Heads, Australia Registered: Jun 2003 posted 03-05-2005 02:21 AM                     Robert No There is no heat filtering Richard Not sure what you mean about using a meter to adjust the lamps. Cin 1 has very nice even light. Cin 2 good spread of light getting a bit darker in the corners of the screen.No hot spots(anymore!) Cin 3 poor light if you want to keep the lenses from getting too warm.But does produce a hot spot if you try and focus the xenon for a brighter screen.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 03-05-2005 02:42 AM                     Hi again Ian - I have always used a rule of thumb on how hot the lenses can get: If one holds the film between thumb and index finger over the lower loop as its coming out of the gate with machine running. If it feels slightly lukewarm then the mirror focus is just about right to the aperture opening. A bit more warmer then the film is getting a bit too overcooked by too much focus of the mirror. One would do this trick on dark scenes for the light being absorbed by the dark emulsion. Also, another trick one can use is to make a loop of solid black film (or black leader from trailer ends) that would go from inside the machine to completely around the front of the machine-from upper guide roller to the bottom guide roller. Run the loop with a mark to call the beginning of the loop with the lamp on and dowser open. The film reentering the machine after a good dozen passes should have cooled down by the time that mark reenters the aperture opening, and if it's remains warm then after the dozen passes, then there is too much light (mirror too close to aperture opening) due to a tight focus of the light beam on the film itself. Lenses are built to take some heat whether what wattage of the bulb. The trick is the bulb focus from mirror to aperture opening that has to be of a proper distance. Hope this helps. Good luck once again. - Monte  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 03-05-2005 07:55 AM                     Sorry Ian, How are you measuring the light on the screen? Do you do it by eye? If so, it's possible that you are making it to bright. I do it by eye first and then check it with the light meter. I'm surprised at how many times I think it's right by eye only to check it and find that I'm 5 or 6 FL to high.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-05-2005 12:21 PM                     Does the lumex have the spread lens in the front without it it produces a cone of light for 16mm and it would overheat lens and produce uneven light  |  IP: Logged Ian Bailey Master Film Handler Posts: 317 From: Nambucca Heads, Australia Registered: Jun 2003 posted 03-05-2005 12:48 PM                     Monte Do you mean the factory recommended distance between the Back of the mirror to the aperture plate when you say "Mirror too close to aperture opening"? Richard I do not have a light meter so I could be making it too bright-I adjust it till i get the best light without a hot spot. Gordon Yes the Lume-x does have the negative lens but it is cracked so i could assume some of the light would not be directed to where it should be. I haven't thought that that could be the cause of the lenses being a bit too warm when I try to get more light on the screen.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 03-05-2005 02:52 PM                     Hi again Ian - Easiest way see if bulb is in proper focus to the aperture, is to have the lamp on with the lens in place. Open the dowser and have the bare light on the screen with the motor running. Draw the mirror focus in until you have a "hot spot" on the screen. Then, draw the mirror focus out to get rid of the "hot spot" until you have an even field of light on the screen. This should be the correct amount of light and at the same, the correct film temperature for the warmth test that I mentioned to you earlier. thx-Monte  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-06-2005 07:26 AM                        Another test of excessive radiant energy is to remove the lens (so it doesn't get damaged during this test) and run a loop of film with dark images through the projector WITHOUT the shutter running. If you can run the loop at least several hundred times without any visible heat damage, you know that you have a "safety factor" of at least two, since a two blade shutter normally reduces the radiant energy by a factor of two. If you have a bad "hot spot", you will see the damage on each frame.: Heat Damage Article Part 1 Heat Damage Article Part 2  |  IP: Logged Ian Bailey Master Film Handler Posts: 317 From: Nambucca Heads, Australia Registered: Jun 2003 posted 03-06-2005 06:47 PM                     Thanks for the Tips John/Monte I will try them next chance I get. Monte That is exactly how I adjust the xenons now. When I first saw the Alignatron I thought this is my answer but when i inspected the mirrors in the lamphouses I found that the hole at the back to be very uneven so i could not see how i could use one accurately enough.The mirrors must be remanufactured from damaged ones.Getting a string alignment kit from Strong(or even getting them to answer an email) seems harder than EATING IDAHO. The next thing i will check is the distance between the back of the mirror to the aperture plate as I doubt whether this has ever been checked. To be able to accurately align all this gear would I'm sure cure a lot of problems. [ 03-07-2005, 02:31 AM: Message edited by: Ian Bailey ]  |  IP: Logged

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