This is topic focus problem due to heat? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Brian Hogan (Member # 940) on 05-04-2002, 12:55 AM:
Spider-Man™ has had a hell of an opening so far and the projection problem i have been having has made it a nightmare. i have a print of it running in a strong projector with a 5K bulb and water-cooled gate. the first half of the movie runs in focus. the second half, however, gets blury in the upper middle of the screen. now of course the torus screens we use dont help with a focus problem, but the exact same projector and print across from the problem projector has been running fine.i dont know if this could be caused by an excessive heat problem making just the second half of the movie out of focus or what. possibly a blockage in the cooling system? any suggestions?
Posted by Paul G. Thompson (Member # 655) on 05-04-2002, 01:33 AM:
Check your xenon lamp focus. Check your coolant temperature about 1/2 an hour or so before the problem starts, and check the temperature after the problem starts. If you are using a coolant circulator, a cheap thermometer dunked in the coolant will work, or just take a thermometer and duct tape the thermometer bulb to the coolant return line. That should give an idea or two. I would suspect you could also have a lens problem. If the lens size of the other side is the same as the problem side, swap the lens and see if the problem follows it.
But the big thing is check your lamp focus first.
Posted by Gordon McLeod (Member # 33) on 05-04-2002, 09:24 AM:
A little bird at a lab told me that Spidrman has silver retained in the image so it is mosre heat suseptable.
It may be necassary to put a fan blowing in on the area between the trap and the lens (poor mans cinefocus) to help
Posted by Paul G. Thompson (Member # 655) on 05-04-2002, 12:50 PM:
I have a 4500 Watt Christie blasting my print of Spiderman, and my focus was rock stable.Gordon is hinting a heat-related problem. Give his method a try, too. 
Let us know what the results of our suggestions were.
Posted by Brian Hogan (Member # 940) on 05-04-2002, 08:06 PM:
the problem has not improved. it seems that the lamps is actually a 6K (rather than 5K), but anyway. the gate and trap have been changed. we have changed the entire lens turret (both flat and scope are blurry) and have added 6 extra fans to the lamp house. we have a fan attached the the back side of then lens gate. we have not checked the temperature of the coolant yet. how would the xenon focus affect the last half of the movie and not the first half? if the lamp were out of focus then would the entire run of the show be blurry?
we have even had a strong tech come out to look at it and even he was stumped. apprently this has been an ongoing issue for sometime. a mystery noone seems to be able to solve. what to do... what to do.
Posted by Gordon McLeod (Member # 33) on 05-04-2002, 08:19 PM:
I think it would be wise to instal a cinefocus type unit
Posted by Jerry Chase (Member # 660) on 05-04-2002, 08:41 PM:
Swap prints. See if the focus problem follows the print or projector. Possibilities:
Is the prime lens the same for both scope and flat? If so, is it shifting focus with heat?
I could be off track here, but is the print on the platter wrapping a little loose on the outside? Heat could be warping the print, but the torque and pressure on the front end of the platter wrap might be mitigating the problem on the first reels. On some platters outer layers don't get "ironed" as much as the inner layers.
Posted by Paul G. Thompson (Member # 655) on 05-04-2002, 10:19 PM:
An out of focus bulb can cause a gradual build-up of heat. The worse the mis-alignment is, the faster it will build up heat.
Posted by Jesse Stanley (Member # 943) on 05-04-2002, 11:50 PM:
Sounds like heat is getting trapped maybe check the coolant.
Posted by John Pytlak (Member # 331) on 05-06-2002, 11:01 AM:
Usually a "silver retention" print process is used for an entire movie, but might it have been used here for just a reel or two?:
http://www.kodak.com/country/US/en/motion/support/processing/skip.shtml If silver is deliberately left in the print to achieve a certain "look", it will absorb more radiant energy and be more sensitive to heat-related problems. With a 6K lamp, you MUST pay attention to proper lamp alignment, heat filtration, and water cooling:
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
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