Film-Tech Forum ARCHIVE: Projection room humidity

This is topic Projection room humidity in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jonathan Worthing (Member # 803) on 10-16-2001, 05:03 AM:

Static is not the projectionists friend. one way to counteract the static is adjust the humidity in the projection room.

My question is does anybody know the optimum % of humidity for the best result.

Posted by Dick Vaughan (Member # 540) on 10-16-2001, 05:26 AM:

We always ask for 50% +/- 5%.. As a guideline IMAX specify 40 - 65% .

Posted by John Pytlak (Member # 331) on 10-16-2001, 09:10 AM:

Kodak's recommendation is 50 to 60 percent RH.

At very high humidity, the gelatin emulsion softens and swells, such that it may scratch easier, build up on hot projector gate components, hold dirt particles, or even get "sticky".

Really low humidity will aggravate static problems, since the film emulsion becomes less conductive. Very low humidity also may cause excessive film curl as the gelatin emulsion shrinks from the loss of moisture.

Ideally, the film should have just a bit of "positive" curl, and lie nearly flat --- this occurs at 50-60 percent humidity.
http://www.kodak.com/US/en/motion/newsletters/reel/september99/pointers.shtml

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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: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Ken Lackner (Member # 1002) on 10-16-2001, 09:16 PM:

JP,

What do you mean by positive curl??

Posted by Steve Scott (Member # 630) on 10-17-2001, 12:02 AM:

30% is nominal for us, but you're right, 50 works well too.

I've found that most wraps, at least here in the midwest, occur in March to May, when it's heating up outside. Or whenever our dehumidifiers break down...

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http://www.mullerfamilytheatres.com

Posted by James R. Hammonds, Jr (Member # 673) on 10-17-2001, 12:10 AM:

Before FilmGuard, I had static problems all over the place.
After FilmGuard I had none.
No difference in humidity.

Posted by John Pytlak (Member # 331) on 10-17-2001, 08:15 AM:

Ken asked: "What do you mean by positive curl??"

As humidity decreases, the gelatin emulsion shrinks as it loses moisture to the air, so it causes the film to curl inward toward the emulsion -- this is "positive" curl. At very high humidity, the gelatin emulsion absorbs moisture and expands, causing "negative" curl. Processed print film has minimal curl between 50 and 60 percent humidity. A hanging short strip of print film in the air can actually be used as a guide to maintaining the proper humidity -- a very slight amount of "positive" curl usually is the optimal position.
Use a dehumidifier if the film has "negative" curl. Increase the humidity if the film has excessive "positive" curl.

Here are links to information:
http://www.kodak.com/country/US/en/motion/support/h1/base.shtml#other
http://www.kodak.com/country/US/en/motion/programs/student/handbook/physical4.shtml

Posted by Jeffry L. Johnson (Member # 453) on 10-17-2001, 11:18 AM:

I attended the IMAX projectionist training seminar in 1999 September. IMAX recommended that the print storage area should maintain 40-60% RH and 21-28'C. The optimal relative humidity is 54%.

IMAX also recommended storing prints emulsion in.

Posted by Ken Lackner (Member # 1002) on 10-17-2001, 12:03 PM:

Quote: "IMAX also recommended storing prints emulsion in."

?????

I have always heard that film should be stored emulsion out. Is the emulsion-in suggestion just for IMAX projectionists?

Posted by John Pytlak (Member # 331) on 10-17-2001, 12:39 PM:

SMPTE Recommended Practice RP39 specifies emulsion-in orientation for release prints, for optimum winding quality and focus stability. However, SMPTE RP39 is based on Kodak performance data for TRIACETATE prints.

Many Film-Tech participants find that platter transport and focus stability of today's 35mm polyester prints seem better with emulsion-out winding orientation. This would be possible, since the humidity curl characteristic of polyester prints is known to be different than triacetate. Frankly, the optimum winding orientation for polyester prints probably depends upon the relative humidity being maintained in the projection room, so the current recommendation is to use the orientation that provides the best transport (e.g., least tendency to "static cling") and best focus stability for the humidity conditions and equipment (curved vs. flat gate, lens type) in your theatre.

Posted by Ken Lackner (Member # 1002) on 10-17-2001, 01:44 PM:

So are IMAX prints still printed on acetate?

How you know if winding emulson in or out would be better for your theatre? Anyway, I'm talking about breaking down the film, when you don't know where it will go. Does emulsion in or out make any difference?

What difference does a flat or curved gate make?

JP- you have provided a lot of valuable information and links on many, many topics, spanning many, many threads. Thank you so much! I have seen older copies of the Kodak projection manual floating around at older theatres I've been to. How can my theatre get a new one? (We don't have any.) thx

Posted by John Pytlak (Member # 331) on 10-17-2001, 02:05 PM:

IMAX prints have always been on Kodak ESTAR base print stock.

With triacetate prints, definitely wind emulsion-in, per SMPTE Recommended Practice RP39. With polyester prints, whichever orientation that seems to give better winding quality (I usually wind emulsion-in).

A curved gate generally helps counteract the heat-related "focus flutter" by gently bending the print lengthwise, giving it some added stiffness in the gate. Most modern lenses are optimized for the more commonly available curved gates.

Film-Tech has ALL the back issues of Kodak's "Film Notes for Reel People" in the "Manuals" section. Recent Kodak publications are available at:
http://www.kodak.com/US/en/motion/newsletters/index.shtml

SMPTE Books, including the recently published Projection Manual, are available at:
http://www.smpte.org/smpte_store/books/

Posted by Freddie Dobbs (Member # 915) on 10-17-2001, 02:58 PM:

Speaking of Film Notes I ran across a copy from 1994 and guess who's photo was in there in the Pytlak's Pratical Projection Pointers

Posted by John Pytlak (Member # 331) on 10-17-2001, 03:19 PM:

I have been writing for Kodak's "Film Notes for Reel People" and "Cinema Notes" since 1979 (although not always with a by-line)

. But the picture never changes much, except for less hair.

Posted by Ken Lackner (Member # 1002) on 10-17-2001, 06:39 PM:

Brad,

I know your Tips page suggests emulsion out for polyester, and that is what I always do. What are your thoughts in light of what JP has said here today? thx.

Posted by Brad Miller (Member # 2) on 10-18-2001, 03:32 AM:

My thoughts are as they always have been. I have posted many times on this in depth on the forum. Just do a search for "emulsion in" and you'll find tons of links.

Or in short, I've yet to find a situation where the film benefited from emulsion in winding. Remember, I've been storing test rolls of film for 12+years now from the early days of FilmGuard development. In every situation, I always stored extra copies "dry" (I used spare trailers that were brand new) with both winding orientations. In every instance, the emulsion out prints were fine, but many of the emulsion in prints had warpage, registration problems, more noticeable shrinkage, etc. While the emulsion in prints that were treated with FilmGuard were for the most part fine, when unrolled there was still some warpage, etc. That is why I recommend emulsion out, all the time no matter what. I've got prints that are over 10 years old that were wound exclusively emulsion out and they still look like they are fresh from the lab with no warpage or curl whatsoever. Still, that is of course not to say that in some place like Alaska or the equator that a different orientation may fare better, but until I see solid proof, I'll continue winding emulsion out. This is definitely moreso important with polyester film stocks though, as polyester stocks come from the lab with a positive curl to begin with and winding emulsion in only exaggerates that curl, which causes focusing problems. Remember, the film will always try and curl outward, away from the hub.

Posted by Jeffry L. Johnson (Member # 453) on 10-19-2001, 02:10 PM:

The last 35/70mm cinema that I worked at full time (1992-2000) was during the transition from triacetate release prints to polyester release prints. I always maintained an emulsion in wind except on those rare occasions to see if a print would behave better running emulsion out on the platter. (Sometimes it did.)

I noticed fewer (or no) focus problems when maintaining an emulsion in wind. When I added trailers that were shipped emulsion out, the focus difference was quite obvious (especially the focus drift within the trailer). After a day or two of running emulsion in the trailers focus point would become the same as the rest of the program that was already running emulsion in.

I had the same results with triacetate and with polyester stock. I maintained emulsion in winding until the cinema closed in 2000.

Core set took longer to change than focus shift, especially with those approx. 1 inch "trailer cores."

In my twenty years experience I've had fewer problems with emulsion in than with emulsion out winding.

Posted by Steve Guttag (Member # 268) on 10-19-2001, 04:15 PM:

I have found that 60%RH is too high...equipment starts to rust up and oxidation starts to be a problem (the rusting can be a real big issue in some areas near salt water too).

I recommend 50%RH +/- 5% based on personal experience.

Steve

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"Old projectionists never die, they just changeover!"