Film-Tech Forum ARCHIVE: AW3 Module Control Fingers Touching Film

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Posted by Ken McFall (Member # 845) on 11-13-2003, 03:31 PM:

I have noticed that the film is running against the profiles of the fingers of the control arm on a couple of my AW3R modules. The timing is correct for the platters and everything is free and not binding in any way. The film seems to cup slightly and fits into the profile of the fingers. We run sound track up so base side is to the left of the control fingers, the side that is rubbing.

I don't have any static problems and everything runs smoothly.

There has been no major scratching but I have noticed some slight marks mid frame on base side, the side that rubs against the fingers, which I can only attribute to this problem.

Any suggestions on how this can be prevented?

Posted by John Pytlak (Member # 331) on 11-13-2003, 03:37 PM:

What is the relative humidity in your projection room? If it is too dry, the film may have excessive "positive" curl (as the gelatin emulsion gets really dry, it shrinks, pulling in the edges of the more dimensionally stable polyester base). Recommended ideal range is between 50 and 60 percent RH. I have heard of a few cases where very low humidity caused enough curl to allow the film surface to contact undercut rollers and guides.

Posted by Ken McFall (Member # 845) on 11-13-2003, 05:38 PM:

Hi Jhon,

well we do have air conditionisg as with nine screens it gets quite warm. I tend to keep the temp down to about 16, where as my team tend to keep it a bit warmer...

I'll give the water in a bowl thing a try and see if that helps.

Posted by Daryl C. W. O'Shea (Member # 1303) on 11-13-2003, 05:47 PM:

Buckets, or bowls of water lying around won't increase the humidity in the booth, at least not to anywhere near you want to be.

Posted by Brad Miller (Member # 2) on 11-13-2003, 06:35 PM:

No, but having bowls of water around does substantially increase the potential of destroying a print or equipment. [Wink]

Ken, don't worry about the fingers. They are fine. There is simply nowhere near enough tension there to matter.

Posted by John Pytlak (Member # 331) on 11-13-2003, 07:07 PM:

First, get a good, accurate humidity gauge to acutally measure the relative humidity. Or at least judge it subjectively by free-hanging a short strip of the print film leader and observing how curled it is. Normally, you should see just a little positive curl, where the film cups in widthwise, with the emulsion side at the bottom of the slight "cup". If the film is a distinct "U" shape across the width, it's likely your humidity is too low.

Best way to add humidity is to use an EVAPORATIVE humidifier that evaporates the moisture off a foam, paper, or ceramic wick. Hot steam vaporizers are very expensive to run, and don't have much capacity. Misting, ultrasonic, or "cold mist" vaporizers/humidifiers should NOT be used, as they spray the mineral laden water mist directly into the air, which can actually get film or electronics WET, and leaves white mineral deposits when it evaporates.

Again, the optimal range is between 50 and 60 percent RH, although as low as the mid-30s is usually not an issue with most prints and equipment. Above 70% is likely to start causing rust and corrosion, affect high voltage electronics (e.g., lamp ignition), and soften the film's gelatin emulsion.

Posted by Manuel Francisco Valencia (Member # 710) on 11-14-2003, 03:58 PM:

Ken

I had this same problem and a few of my prints had random line scratches in the middle of the piture. They were very faint which led me to believe the arm was causing it. I did not find the picture touching anything anywhere else in the picture area so that narrowed it down too. All I did was remove the arm from the brain and moved one of the fingers. I believe it is the right one that you can move about 1/16 of an inch over. This gives the film more room and allows it to tilt to the side so that only the edges are touching the fingers. This was a time when our ACs were going out like crazy and the extreme heat just killed the humidity in our booth.

Posted by Ken McFall (Member # 845) on 11-16-2003, 07:20 AM:

Thanks everyone for your replies.

The problem is only with a couple of prints so I'll need to key an eye on them. It is something I've seen before on a Linton platter but again it was only occasional.

Its worse when the film is feeding straight into the fingers and the rollers. Its fine when there is a definate curve to the film which gives it more stability.

As for controling the humidity.... as we don't get any brain wraps I doubt the company will see it as an issue.

Thanks again.

Posted by Darren Briggs (Member # 1071) on 11-19-2003, 03:24 PM:

Hi Ken Hope you are well and having fun,

The bucket of water in the corner of a projection room does work.
THX even sent out a memo which i believe is on this website regard the THX greenhouse to help reduce static on a print.
This involved puting a small tub of water in the center of the film and a cover over the print, overnight.
Works a treat.

Take care,

Darren

Posted by Brad Miller (Member # 2) on 11-19-2003, 05:36 PM:

Joe, I think that first "booth training" video of yours was too subtle with the water trick. [Razz]

Posted by Joe Redifer (Member # 3) on 11-19-2003, 06:10 PM:

That was made 5 years ago! If I had the resources we do now, I would have made the water spill onto a print! I should have done that anyway... I wasn't shooting that portion at my theater, so it wouldn't have ruined any of my equipment.

Posted by Jeff Skallan (Member # 891) on 11-20-2003, 12:36 AM:

quote:
That was made 5 years ago! If I had the resources we do now, I would have made the water spill onto a print! I should have done that anyway... I wasn't shooting that portion at my theater, so it wouldn't have ruined any of my equipment.

Joe, you are now officially BANNED from my booth. By the way, I'm still waiting for the royalty check in the mail for my cut of all training video downloads. Pay up or I'll have to sue your ass! [Razz]

Posted by Joe Redifer (Member # 3) on 11-20-2003, 12:38 AM:

Sorry Jeff, I am way too busy counting all of the money that pours in from each download of said Training Video to make time to write you a check. [Smile]

Posted by John Pytlak (Member # 331) on 11-20-2003, 01:44 PM:

The use of a damp sponge in a bowl, "tented" with the print on the platter was proposed as a "last resort" method of adding some moisture to a very dry environment years ago, before the invention of a transparent process-surviving conductive anti-static layer on the backside of Kodak VISION Color Print Film. You needed to be VERY careful that the print didn't get physically wet.

If your projection room is too dry, the only effective way to add moisture is with the existing HVAC system, or with an evaporative humidifier. Bowls/buckets of water on the floor do virtually nothing to increase humidity, but damp mopping the floor could help add moisture and keep the floor cleaner too.

Even with anti-stats on the film, proper humidity control is a good idea, if only to maintain the optimum curl of the film.