Film-Tech Forum ARCHIVE: Shadows and heat shield??

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Posted by Ben LaCrosse (Member # 4662) on 02-24-2008, 05:03 AM:

I need help.

simplex pr1060
Strong lamphouse

We have one House that has terrible shadows in the upper and lower right hand corners of the screen. In Flat it is more noticeable than Scope. It's like you're watching a movie through a yellow telescope. Yup, picture is yellow for some reason too.

I've determined it is not aperture plate related. The lamp house has not been moved. That is about all I've been able to come up with though.

There is this piece of coated glass in between the lamp house and projector. I think it is the heat shield. Any ways, that has a hole in the coating. It just looks like the coating has been burned away. It's about a half-dollar size hole. Not in the glass, but the coating.

What is this hole doing to the picture?

I am trying to avoid working with the lenses. I have a feeling that's where this will be going.

Posted by Louis Bornwasser (Member # 3063) on 02-24-2008, 08:53 AM:

Does the scope picture look yellow too? Louis

Posted by Mark Gulbrandsen (Member # 72) on 02-24-2008, 09:11 AM:

That "hole" is there because the heat filter has faded or the coating has peeled. Either way thats not going to get you a yellow tinged image. Check your reflector carefully with a flashlight. You may find the coating on it has peeled or blacked from lack of proper exhaust. This can very definately cause the yellowish cast you mention. If its a Stupid Highlite then its gonna cost a byundle to replace the mirroe... we actually replace the enmtire plenum in that lamphouse with another make plenum... its LESS EXPENSIVE and gets you more light.

Mark

Posted by Peter David Bruce (Member # 4447) on 02-24-2008, 09:15 AM:

we are running those Stupid Highlight II houses. they arent bad. infact they are pretty good but then again weve never had a mirror go bad/get damaged. 7 years without a fault... any time now. Couldnt also some kind of damage to the porthole glass be it? Perhaps some spilled sticky Fanta or Tango on the window.

On a serious note, we have had some strange colour casts on one of our screens before. Turned out we had a bad lens. Now replaced with an ISCO.

Posted by Mark Gulbrandsen (Member # 72) on 02-24-2008, 09:22 AM:

Peter,

In all fairness a mirror failing like this can happen in ANY lamphouse if the exhaust blower dies and you don't have stack switches installed to kill the lamp... a burn't reflector is not something that eventually happens... Its just that the the Highlite Mirror is around 2 grand to replace while most others cost far less...

Mark

Posted by Peter David Bruce (Member # 4447) on 02-24-2008, 09:25 AM:

Weve just replaced two front blowers... now i know what they are for. cheers

Posted by Ken Lackner (Member # 1002) on 02-24-2008, 12:59 PM:

If I am not mistaken (and someone will no doubt correct me if I am), the front blower on the Highlight II is there to cool the front end of the lamp, not the reflector.

Mark, when you need to replace a reflector in a Highlight II, what do you replace it with?

Ben, the shadows may simply be due to the lamp not being properly aligned/focused. If you turn the lamp focus control, can you get the shadows to go away while still maintaining even and adequate light on screen?

Posted by Mark Gulbrandsen (Member # 72) on 02-25-2008, 08:23 AM:

I haven't had to replace any mirrors in Highlite 2's as of yet.... just in Highlite 1's. We use the kit to replace the highlite 1 mirror thats sold by Bill Younger. It uses a glass mirror and the light output is just over double the old Highlite 1 mirror. I believe the cost is about 500.00 less than the new Highlite 1 mirror from Strong which goes for nearly 2K!! Even the Christie Plenum kit is less than that....

Mark

Posted by Ben LaCrosse (Member # 4662) on 02-26-2008, 02:24 AM:

Yeah they are Highlight lamphouses. Don't know if I or II. Will check when I go back to work on thurs.

I will also try the lamp focus screw, as well as check the reflector. If I remember correctly it did have pits in it, like old chrome has.

This same house will also stick in the ignition phase of lamp striking, occasionally. It is like the striker stays lit even though the bulb has already been struck. I think that makes sense.

And so the hole in the heat filter will not change how the light passes through, for shadows sake.

Man, I hope no one on this forum accidently sees a movie in this auditorium. Guranteed, straight to the 'outing bad film handlers thread'. It is bad. I feel so sorry for the customers.

any ways...

Posted by Ben LaCrosse (Member # 4662) on 03-23-2008, 03:52 AM:

Update and another question.

The shadows and the tan color exist only in flat. So I am thinking toasted lens. That leads me to believe the lens was exposed to naked light for too long and it killed the lens.

That would also explain why the coating on the deflector lens, or heat shield, looks to have a hole burnt through it.

The projector in question has had a history of random failures to shut off after a movie. Thus the motor keeps running and the lamp stays on. The three times it has happened to me I have caught it within 30 seconds. I can't say the same about the other projectionists. It wouldn't be beyond the realm of possibility for them to not catch it even 30 minutes later.

So my question is, if the projector stayed running after a show break and no one was there to shut it off, could that burn a hole through the coating of the heat deflector and kill the lens as well?

Wouldn't the douser prevent this from happening?

any thoughts...

Posted by John Hawkinson (Member # 1135) on 03-23-2008, 08:23 AM:

Short answer: yes, it is quite possible.

What wattage lamp? What manufacturer and model lens?

It's a little surprising, but film running through the gate of the projector actually takes away a lot of the heat from the system. For many older lenses, running "open gate" (no film) and projecting white light for an extended period of time can be enough to permanently damage them, because they get a lot hotter that way.

This all pretty much assumes your douser was open. Do the projector's faults not extend to failing to close the douser at the end of the film as well?

--jhawk

Posted by Louis Bornwasser (Member # 3063) on 03-23-2008, 11:04 AM:

I would swap the flat lens with another projector. Then I would swap the heat filter/lens with another. That way you can determine exactly what is wrong.

It is possible that only one or the other is actually bad.

Why would a bad heat filter not show on scope also? If the burn is exactly in the center. then there might be enough unburnt area around the burned center to give a whiter light on scope, which uses more of the lens. Flat relies on lens magnification; that is why it is always darker than scope. Louis

Posted by Jeremy Weigel (Member # 4208) on 03-23-2008, 11:02 PM:

I have 2 Isco UltraMC's 130mm with scope attachments that had what I thought to be dust on the inside of the primary(?) element. They have been this way for some time. I finally got a lens spanner tool and removed the element to clean it, but it's not dust. After close inspection, the specks look like tiny bubbles embedded in the element. Both surfaces are smooth. Are these elements possibly burnt? The image on screen looks sharp and the light output is white.