Film-Tech Forum ARCHIVE: Loop Flash?

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Posted by Josh Jones (Member # 447) on 08-05-2002, 11:20 PM:

Lately I heard of a phenomenon known as loop flash. It is supposively noticeable only at close range to the screen and studio people are bitching about it. I have also heard Kinotone projectors dont have this problem, but others do. Anyone know more about this?

Josh

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P.S. It can be solved by moving the picture aperture to a higher position in the gate, farther from the lower loop.
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"Film is made of silver, video is made of rust"
'nuf said

Posted by Manny Knowles (Member # 1171) on 08-07-2002, 12:09 AM:

It might help if you described the phenomenon...somebody may have encountered it and called it by some other name.

Posted by Josh Jones (Member # 447) on 08-07-2002, 12:21 AM:

I personally havent seen this phenomenon, But I have heard it is noticeable on at least simplex machines when running RP40 and when sitting at a close range to the screen. Studio people are the only ones who seem to be complaining about it. Because Kinotone machines have the aperature placed higher in the gate, they do not suffer from this.

Thats all I know.

Josh

Posted by Joe Redifer (Member # 3) on 08-07-2002, 02:05 AM:

I have been AT the screen while running RP40 on a Simplex and a Christie, and I don't recall any onscreen differences between the two. Unfortunately for me I have never even seen a Kinoton in operation.

Regardless I didn't see anything to bitch about as I was standing at the screen with the RP40 running, and I am quite the anal retentive ass when it comes to projection.

Posted by Paul G. Thompson (Member # 655) on 08-07-2002, 03:30 AM:

I wonder if Josh might be referring to a "rubber screen". That's when there is image flutter near the center of the screen.

I think I am using the correct term in describing this... If memory serves me correctly, I picked up that term from the Kodak's "Reel People" publication a long time ago.

I have seen this occur in straight gate machines on occassion. There are multiple causes of this problem.

However, I have not seen that happen in a curved gate machine.

Posted by David Stambaugh (Member # 1102) on 08-07-2002, 11:48 AM:

Paul, Occasionally it looks like bright objects in the center of the screen, like text, seem to be shifting left/right/left/right slightly with each alternating frame. Yet the rest of the image seems steady. Is that "rubber screen"?

Posted by Pat Moore (Member # 380) on 08-07-2002, 12:20 PM:

Hi; "Loop Flash" is a new term to me. Love to know more about it...

Pat

Posted by Bill Gabel (Member # 1105) on 08-07-2002, 12:57 PM:

Are you running regular release prints or work prints???

What type of splices??

Because if you are running work prints, you will have different
types of splices to deal with. (inviso , 8 perf single sided splices
...)

I have a pair of Magna-Tech PR-135 projectors, which are the
studio version of the Kinoton FP20 projectors.

Posted by Josh Jones (Member # 447) on 08-07-2002, 02:08 PM:

Pat,

One of your simplex guys mentioned it, I think his name was Jerry Bigalo(sp?). Anyway, he said the studio guys complain about it once in a while.

Josh

Posted by Paul G. Thompson (Member # 655) on 08-07-2002, 08:21 PM:

David, I think it was some kind of flutter. Maybe John, the "Human Link" will chime in and cite the definition of a rubber screen. I no longer have the Reel People Magazine published by Kodak.

Posted by John Pytlak (Member # 331) on 08-07-2002, 09:23 PM:

"Focus Flutter" is a heat-related effect:
http://www.kodak.com/US/en/motion/newsletters/pytlak/fall97.shtml
http://www.kodak.com/US/en/motion/newsletters/pytlak/winter97.shtml

Be sure your lamp is aligned properly, with no hot spotting, and that you are using efficient heat filtration. Adjusting gate tension can sometimes help. High film moisture levels (freshly processed prints, high humidity) can aggravate the flutter as the radiant heat of the lamp drives out moisture, causing a rapid change in curl.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Josh Jones (Member # 447) on 08-07-2002, 10:59 PM:

its not focus flutter, its something else.

Posted by Paul G. Thompson (Member # 655) on 08-07-2002, 11:47 PM:

John, how does Kodak's "Reel People" publication define "rubber screen"? I don't have a copy of that publication any more.

Posted by John Pytlak (Member # 331) on 08-08-2002, 05:50 AM:

Paul: I don't recall that Kodak ever defined "rubber screen", except perhaps as a slang term for focus flutter. Can you recall the approximate date of the issue you saw it in?

Posted by Paul G. Thompson (Member # 655) on 08-09-2002, 03:50 AM:

John, I am sure it was a slang. Maybe that's what it was referring to. Thank you for looking it up. I think that issue goes back to the mid 80's, maybe even earlier. It was a very popular magazine many theatres ordered specifically for a projection booth reference. It was about 3/8 of an inch thick.

David, I don't know what it is called. I wonder if Josh might have been referring to what you described.

Paul

Posted by Jeffry L. Johnson (Member # 453) on 08-09-2002, 08:52 AM:

Maybe this was the source of "rubber screen"?

Film Notes for the Reel People
Troubleshooting and Prevention of Damage
Kodak Publication No. H-50-4

Image Sharpness
The Heat/Light Conspiracy
"Screen image focus problems can arise when the heat becomes too great, especially if the humidity is high. New prints are more often involved than seasoned prints. If all of these adverse conditions are present, the screen image will appear soft and no focus trim will help. This is called flutter. As conditions become worse, the image will begin to go in and out of focus erratically making the screen appear to be made of rubber."

Posted by John Pytlak (Member # 331) on 08-09-2002, 09:39 AM:

Jeffry: Thanks. I was a mere youngster at Kodak when that one was written by Paul Preo in 1977.

As I suspected, it was another term for "focus flutter".