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

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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

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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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

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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

?????

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.

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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

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?

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/

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