Film-Tech Forum ARCHIVE: Differences between DKP70mm and RPG prints

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Posted by James B. Openshaw (Member # 1310) on 08-26-2004, 10:08 PM:

It appears that I've noticed something with films distributed from RPG, they're filthy. No matter how many times I change out the PTR's, wiper bars, and wiped down the field flattener after each show, it seems that the on-screen crap isn't reduced by that much. The prints we receive from DKP70mm we've had practically no problems with concerning dirt (new or used prints)

Has anyone else had similar experiences with RPG prints (e.g. Lewis & Clark, Bugs, Mysteries of Egypt, Forces of Nature) and found methods to get most of that crap off of them? Also, could anyone possibly tell me what DKP could be doing that RPG isn't?

Posted by Dan Suomi (Member # 2585) on 08-26-2004, 10:57 PM:

Gosh I wish I could respond anon on here. I'll say this your not the only one who has issues with RPG films. I'll leave it up to others to post thier comments, I'm just not comfortable of doing it on here. You should go check out 1570.com for comments about RPG.

As to fixing the problem, you are doing everything right in trying to minimize the problems you are having. Keep doing what you are doing and eventually things should clear up for you.

Posted by Stewart Anderson (Member # 1809) on 08-29-2004, 01:05 AM:

RPG STRIKES AGAIN!!!

We have had trouble with stretched splices in the past. Now because of our new film Bugs 3D being tape spliced from RPG I thought I would just replace the splices between reels ONE and TWO with ultrasonic, because these are always the splices that stretch due to most of the tension being present on the beginning of the film during rewind. I replaced only these splices with ultrasonic because I knew RPG was already going to be upset with me for replacing even those two splices. Now, I also checked all of the splices on that movie and I always check tape splices on a biweekly schedule. But after only TWO DAYS of running the film, the splice between reels TWO and THREE stretched. un-freakn-believable!

Posted by Gordon McLeod (Member # 33) on 08-29-2004, 07:41 PM:

Stuart said"I thought I would just replace the splices between reels ONE and TWO with ultrasonic,"
Well I hope you inserted 2 frames of black to replace the two frame you had to cut out to make the ultrasonic splice
If you didn't then you have trashed a print as sync will not be maintained in many other systems

Posted by Stewart Anderson (Member # 1809) on 08-30-2004, 09:34 AM:

of coarse. [beer]

Posted by Adam Martin (Member # 641) on 08-30-2004, 05:49 PM:

quote: Gordon McLeod
If you didn't then you have trashed a print

And if you did, you trashed the print. A black flash at every reel change in a 15/70 print is a 1/12-second flash every three minutes. Might as well Crap Code the print while you're at it.

A print with slugs would be refused by my booth.

Posted by Brian Michael Weidemann (Member # 2243) on 08-30-2004, 08:26 PM:

What's wrong with just re-TAPING a splice that's stretched or going bad? Ooh, ah ... ultrasonic, ultrasonic. Big deal! [Razz]

Posted by Kyle McEachern (Member # 2250) on 08-30-2004, 09:35 PM:

quote: Brian Michael Weidemann
ultrasonic, ultrasonic. Big deal!

That's a debate that's raged many times over...but yeah, if a tape splice is stretched, it should get re-taped, because as Adam said, 2 frames of black every 3 minutes = unacceptable. And not only that, properly-made tape splices will last for months/years without problem.

As for RPG...I don't think I've ever met a person who has preferred them to DKP. All that you can do is clean up the prints with PTRs and/or ask for prints to come as reels and not pre-built so you don't have to deal with their building methods.

Posted by Stewart Anderson (Member # 1809) on 08-31-2004, 12:36 AM:

I think the life of a tape splice is variable, it depends mostly on the equipment. And on a MKI TYPE of reel unit the most risk of stretching is at the beginning of the film (due to tension on rewind). On my equiptment (from CDC) I'm screwed if don't stub out the splice and screwed if I do (for the reasons you guys listed). Now the splice that caused a reel replacement looked perfect when it was first wound on to the platter, but after ONLY TWO DAYS it stretched. So in my case I think I'm LESS screwed in stubbing out splices at the beginning of the show. Or if I can convince my bosses of spending the extra money for ultrasonic spliced prints or non pre-built print. Like that'll ever happen [Cool]

Posted by Jack Ondracek (Member # 1466) on 08-31-2004, 02:12 AM:

I have no clue what film you're running... or what your projectors are..

but...

how can you be putting so much tension on your film that it causes tape splices to stretch? I thought 70mm equipment was supposed to be pretty easy on film?????

How can it differ that much from 35? I have no stretching problems here.

Education time, I guess! [eyes]

Posted by Gordon McLeod (Member # 33) on 08-31-2004, 09:36 AM:

I check all prints with tape splices every two weeks for stretching or if I see them flashing on the port as they go through
As a rule we don't accept any new print preassembled but do it ourselves with the UltraSonic
The MK1 design by itself is not as much of an issue if it wasn't for the fact that our prints are stored on edge and rolled out of the booth to a storeroom down the hall and to prevent excessive tear dropping we use the highest rewind tension we can get

Posted by Brian Michael Weidemann (Member # 2243) on 08-31-2004, 02:49 PM:

The projector itself is gentle on film. It's the higher speed rewind time, after the show, that tends to cause the stretching, I believe.

I work with the QTRU (center-feed) unit now, so I don't have splice issues that can arise during rewind (since there's no rewind stage). If any splice will stretch, it's the one holding the leader to the slug, which just sits there under tension between loading the show and starting the show. If no tickets are sold for that first one, then that splice is being pulled on for a good three hours. But then, this one is easy to check and replace, if need be.

Posted by Brad Miller (Member # 2) on 08-31-2004, 03:45 PM:

Not being an IMAX guy I am going to chime in here anyway.

When I visited Adam's booth in Sacramento, the first thing I noticed was that his MKII was rewinding very slowly, perhaps only 2-3X normal speed. However all other rewinding IMAX transports rewinding insanely fast. I asked him and he said he intentionally set it to rewind slowly since they always alternate movies.

Really, this should be standard practice. I saw no cinch marks on screen and the rewinding was slow and gentle. He also had no issues with tape splices stretching.

James, aren't RPG prints commonly Photoguarded?

Posted by Gordon McLeod (Member # 33) on 08-31-2004, 06:26 PM:

Brad said"perhaps only 2-3X normal speed. However all other rewinding IMAX transports rewinding insanely fast. I asked him and he said he intentionally set it to rewind slowly since they always alternate movies.

Really, this should be standard practice. I saw no cinch marks on screen and the rewinding was slow and gentle. He also had no issues with tape splices stretching.

James, aren't RPG prints commonly Photoguarded? "

The original MK1's had a 3 phase variac control the power to the motor as well as a dynamic breaking control to provide tension
Usually the balance of tension to speed ended up with about a 10 min rewind for 40min of film to achieve a tight enough wind that the platter can be stood on end for storage

RPG like others photoguards on request only and to my knowledge RPG will ultrasonic splice if requested but if they could get the rest of there consistancy up it would be nice

Also not every place alternates movies projectionists don't get to choose the schedule nor the prints they have to show [Mad]

Posted by Stewart Anderson (Member # 1809) on 09-01-2004, 09:51 AM:

On the CDC "version" of the MK1 there is a 1 to 10 scale for rewind. I don't know what the reel MK1 is like... Anyway we only rewind at 5 1/2. This will rewind a 40 min movie in about 20 minutes (2X speed). But the stupid thing still stretches. [bs]

Posted by Mark Gulbrandsen (Member # 72) on 09-01-2004, 09:07 PM:

Stewart,
I don't think that the majority of your stretching is happenning in rewind. I would look more closely at the take up tension as the film is comming out of the projector(still warm of course!). The splice is exposed to quite a bit of heat and that heat will easily soften up the adhesive on the tape. Then as its wound up the pull from take up stretches the splice a bit each time the film is run. Then rewinding each time will stress the splices a tiny bit more. And so it all adds up to a big headache! My feeling is that your main problems are:

1. The tape you are using is not adaquate enough for the job and that you don't re-do the tape splices at regular enough pre-determined intervals to see any real reliability.

2. You need to experiment to determine where the brunt of the problem lies and what aspect of the operation is causing them to stretch the most. Only after doing this can you arrive at any logical decision as to how often you need to re-do your splices.

3. Its a really easy experiment with some junk film to find out which mode of operation IS actually affecting the tape splices the most and you can easily calculate how often from those experimants based on the number of passes of the test film that you would need to re-do them. Of course this would have to be done before or after normal hours [Eek!]

.

Mark @ CLACO

Posted by Stewart Anderson (Member # 1809) on 09-02-2004, 10:24 AM:

I think the take up tension (5 lbs) with the heat of freshly being exposed on screen is a factor. But when CDC was hear they ran all sorts of test to try and figure out the cause. They were just able to rule out the projector as being a cause. They did test the reel unit (kinda)... But I'm still leaning toward the tension on rewind since all of the splices that have stretched in our booth have been near the beginning of the film.

Posted by Bob Brown (Member # 1205) on 09-02-2004, 10:30 AM:

Well, after reading this thread, I am sooooooo glad that I have a QTRU [thumbsup]

I have inspected prints with 500 runs on them and most of the splices are still tight and did not need to be replaced. We here in my booth, we inspect each print after 125 runs, or if something gives us the reason to check it sooner. So far, the prints and splices have check out GREAT!!. BTW, I am scheduled to get the QTRU upgraded to 150 min decks real soon for Polar Express. IMAX is upgrading decks 2-5 to 150 minute capacity, with deck 1 at 90 min capacity. 71" diameter platters. Can't wait for this! [Eek!]

Posted by John Pytlak (Member # 331) on 09-02-2004, 03:57 PM:

quote: Stewart Anderson
I think the take up tension (5 lbs) with the heat of freshly being exposed on screen is a factor.

5 pounds of tension is very high, even for 70mm film. [Eek!]

For 35mm prints, SMPTE Recommended Practice RP106 says:

quote:
2 Film tension
Film tension under normal operating conditions shall
be 1.7 N to 4.4 N (6 ozf to 16 ozf).

5 pounds of tension would be very likely to make a tape splice stretch, especially if it was under constant tension as head leader might be prior to starting.

Posted by Adam Martin (Member # 641) on 09-02-2004, 04:11 PM:

Maybe he's referring to a 5-pound weight (or hydraulic arm) distributing the tension out over a cluster of rollers (similar to the take-up variac assembly on a SPECO LP-270). That would give you more than one strip of film to bear the tension.

Posted by Mark Gulbrandsen (Member # 72) on 09-02-2004, 06:40 PM:

Stewart,
It wouldn't matter if its near the beginning or at the end because your system is one that has constant tension through out the wind process on take up. Rewind should also be constant tension if its setup correctly. Thats just the way the Baldor drive system works with the tension arm in your case. You should aquire a tension gauge and verify things yourself before you ruin a nice print!

Mark

Posted by Stewart Anderson (Member # 1809) on 09-03-2004, 12:02 AM:

Adam: that is exactly what I was refering to, everyone seems to have their own name for it (accumulator, dancer, pulley system...whatever you want to call it). CDC told me that is the normal tension for take up. Does anyone know what the tension is on the reel MK1? I would love to tell CDC "nope, that IS NOT RIGHT!".

Mark: I think the Baldor VSDs do have the programmable capability for the left platter to release tension by "helping out" the right platter rewind (given the film is rewinding from left to right). This would keep the constant tension from beginning to end. Unfortunately, CDC has only been able to have the left platter increase tension (I think they did this to keep the film on the rewind roller, they did have some trouble with this when they were programming it). Right now it is programmed to have the most tension at the beginning of the rewind and then it releases tension toward the end of the rewind. So near the end of the rewind (at the beginning of the film) it will no longer increase the tension, but due to the circumference/RPM difference it is still adding a lot more tension then it should. In fact, a lot more then it would ever add at the beginning of the rewind. Do you have any ideas for measuring/calculating the tension on the rewind arm? I havn't been clever or creative enough my self. Out of boredom I also included this graphic for anyone reading this who hasn't worked with the MK1 design.

Everyone: I greatly appreciate your input!

Posted by Gordon McLeod (Member # 33) on 09-03-2004, 10:08 AM:

On the MK1 the rewind brake is speced at 4lbs
the projection mode breaks are spec at 3-6lbs
Note that this is not the direct tension on the film but measure with a set of scales pulling on the flange of the reel drive plate