Film-Tech Forum ARCHIVE: MPX Field Flattener Question

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Posted by Mark Lensenmayer (Member # 134) on 06-28-2006, 06:38 PM:

For the second time, my "Imax Experience" was plagued by a constant dirty spot on the field flattener. Same spot on the screen--20 seconds on, 20 seconds off.

Is it possible, on an MPX unit to do a better job of cleaning the field flattener during the running of a film, or once dirt gets stuck, it stays until it is cleaned.

I spoke to the management of the Columbus OH Easton AMC 30 about this, and they indicated that they cleaned it after each screening, but there wasn't anything they could do during the running of the picture.

Also to note is that there is not a dedicated operator in the booth with this machine.

Is embedded dirt a design flaw, or is there a solution? That spot on the screen drove me CRAZY during most of the picture.

Note: the dirty spot was even noticed by my wife, who is not nearly as picky about these things as I am!

Posted by Brian Michael Weidemann (Member # 2243) on 06-28-2006, 07:44 PM:

I don't know specifically how the MPX field lens cycle is operated, but the specks of dust sticking and not wiping away isn't particularly a design flaw (unless it's actually a nick in the glass, which could appear the same as debris). This happens with the GT on occasion, with a stingy speck. The best we can do is set the auto-wipe to double, and manually set the non-specked part into the aperture. Or, just turn the wipe off. But then, any new specks that could be wiped, won't be.

If they say there's NOTHING they can do except clean it between shows, I'm under the impression the MPX system doesn't have an Adjust screen or a manual field flattener wipe button, then?

Posted by Christopher Seo (Member # 7) on 07-01-2006, 12:12 AM:

If the MPX system does not have a way to manually wipe the field flattener, it would be pretty lousy. I suspect the culprit is the lack of a dedicated IMAX projectionist. It's often the case that one half of the field flattener is dirtier than the other, but of course it takes a person actually looking at the screen to figure that out and judge whether to do a single or double wipe and when to do it so as to be minimally obtrusive. Auto-wipe has certainly ruined a few IMAX presentations for me.

Posted by Mark Lensenmayer (Member # 134) on 07-01-2006, 09:38 AM:

Christopher, I agree that unattended operation is part of the problem. I believe they are selling the MPX system as being designed to just press the start button and walk away.

The MPX field flattener seems to cycle constantly during the film. The dirt spot is there, then not at about 20-second intervals.

According the the AMC management, once a dirt speck is stuck to the flattener, it can not be taken care of during the running of the film. Unfortunately, both times I've experienced this, the spots have been close to the center of the screen where most action is taking place. It is very hard to miss or ignore.

I'll go back out for ANT BULLY (if it plays there) and see what happens then.

Posted by Gordon McLeod (Member # 33) on 07-01-2006, 12:55 PM:

Sometimes even on a regular flatner a bit of dirt will stick that the wiper bars can't remove so it is there till the flatner can be pulled out at the end of the show and hand cleaned

Originally the field flatner was two seperate peices of glass that one pushed by hand down the apperture block and the old one popped out into a pan under the block and yiou cleaned it by hand. Not a pretty sight when the odd time both popped right through

Posted by Dick Vaughan (Member # 540) on 07-02-2006, 05:41 AM:

quote: Gordon McLeod
Originally the field flatner was two seperate peices of glass that one pushed by hand down the apperture block and the old one popped out into a pan under the block and yiou cleaned it by hand. Not a pretty sight when the odd time both popped right through

That used to keep us busy alright. I remember when we were going through a real bad time with a badly photoguarded print of To Fly which was shedding like crazy. We must have changed that field lens at lease 50 times a show! [scream]

The highly sophisticated piece of wood provide to knock the flattener through is now part of the National Cinematography collection here in the Museum. It still carries the inscription "This Side Towards Screen" to stop us getting confused [Big Grin]

Posted by Brian Michael Weidemann (Member # 2243) on 07-02-2006, 06:10 AM:

Now how visible on screen was THAT set-up when pushing the new field lens into place?

Posted by Gordon McLeod (Member # 33) on 07-02-2006, 10:25 AM:

Actually it wasn't that bad and it did have the advantage that sticky ones could be eliminated as you hand cleaned each segment
It definetly wasn't as intrusive as the IWERKS CDC two peice with the metal seperator is that to get around a patent required