Film-Tech Forum ARCHIVE: Fox Sprockets?

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Posted by Joe Beres (Member # 678) on 10-12-2001, 10:34 AM:

I just receive a print of the Umbrellas of Cherbourg that was last shown at the Brooklyn Museum of Art. Along with the print came a projection report sheet that was filled out by the projectionist there. (If by chance that projectionist or anyone associated with them reads this, thanks for the great information and for caring enough to make the report. I think I am going to copy the form and use it myself here.) Anyway, in the picture format section of the report, there is a checkbox for "Fox Sprockets." What are they? What do you know about them?

Posted by Bruce McGee (Member # 131) on 10-12-2001, 11:14 AM:

Fox sprockets were an idea from Twentieth Century-Fox. When Cinemascope came out, there was not enough room on the 35mm film for the image and the four magnetic soundtracks. The solution was to use a smaller sprocket hole. I dont think that there was an optical soundtrack on these magnetic prints, either.

I have a 50' piece of film with the mag tracks and 'Fox holes.' Unique, to say the least.

No, it cant be run on standard sprockets, unfortunately.

Posted by John Pytlak (Member # 331) on 10-12-2001, 11:18 AM:

"Fox Sprockets" are the smaller "CS" perforations that were developed for use with the original "CinemaScope" system to provide the additional space needed for the magnetic stripes. The normal "KS" perforation is 0.1100 x 0.0780 inches, whereas the "CS" perforation is 0.0780 x 0.0730 inches. You MUST use sprockets made in accordance with standard SMPTE 242, having a tooth width of either 0.040 inches (Type S, or "Fox Tooth") or 0.072 inches (e.g., LaVezzi "VKF" sprocket). Wider sprocket teeth (e.g., LaVezzi "PosiTrol" sprocket) will severerly damage the perforations on print film perforated CS-1870. Likewise, your splicer needs to have the narrower "CS" registration pins, or the film will be damaged.

Here is a link to information on Marty Hart's "American Widescreen Museum" website:
http://www.widescreenmuseum.com/widescreen/wingcs1.htm

Here is information on the compatible "VKF" sprocket design:
http://www.lavezzi.com/PDFs/SprocketPDFs/VKFSprockets.pdf

I assume your theatre is properly equipped to handle and play magnetic striped prints? Even if you play a later magnetic/optical track print on an optical reader, be sure you do not damage or accidently erase the magnetic tracks (degauss film path, be sure tracks aren't abraded, etc.).

------------------
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 Mark Gulbrandsen (Member # 72) on 10-12-2001, 01:55 PM:

I remember reading an article years ago in International Projectionist that said that Fox Hole sprockets are much stronger than standard perfs are. You will be fine as long as your projector does not have any standard tooth sprockets on them. It is pretty rare to see standard tooth sprockets anywhere these days. Usually on an old relic typr projector.
Mark @ GTS

Posted by Leo Enticknap (Member # 534) on 10-16-2001, 02:13 AM:

Possibly, but that article was probably talking about new film stock. If this is an original release print of 'Cherbourg' from the 60s then the triacetate base is likely to have shrunk and gone quite brittle by now.

My gut feeling on this one would be to check the condition of the perforations carefully before running the print.

Posted by Steve Guttag (Member # 268) on 10-19-2001, 08:03 PM:

Beware of using VKF sprockets with fox hole films. While the VKF sprocket was designed to work with CS perfs...they do not allow for hardly any shrinkage. Virtually all of the CS perf films I've seen as of late will not sit well on the VKF sprocket due to shrinkage. I now only recommend using CS sprockets if you plan to run CS perfs.

As a cheater for a Simplex...thread your feed sprockets such that only one pad roller engages...that is, on the top sprocket use the first pad roller to keep the film off the sprocket an let it go though the second padroller (the one closest to the upper loop) normally.

For the intermittent you are hosed though...if the film has shrunk enough, it will buckle in the gate area since it can't wrap the the tight intermittent sprocket.

Also, if you haven't done so already, before running mag film, switch to delrin padrollers (no steel!).

Steve

------------------
"Old projectionists never die, they just changeover!"

Posted by John Pytlak (Member # 331) on 10-22-2001, 01:47 PM:

Aging shrinkage of old triacetate film can be as high as about 0.50 percent, whereas modern ESTAR base color print film is only 0.04 percent:
http://www.kodak.com/country/US/en/motion/support/h1/base.shtml#table01

Posted by Leo Enticknap (Member # 534) on 10-24-2001, 02:14 AM:

A train of thought which leads me to speculate that if the perforations are a lot smaller relative to the projector's sprocket teeth to start off with, then this amount of shrinkage could potentially cause a greater risk of perforation damage during projection than with an element which has full-size perforations.

If acetylation has made the element abnormally brittle as well, then those perforations would be even more susceptible to tearing.

Also, do I remember correctly that 'fox hole' perforations have right-angled corners whereas conventional release print perfs have rounded corners? If so I would have thought that an acetylated element would be even more of a risk in projection.

Posted by John Pytlak (Member # 331) on 10-24-2001, 07:22 AM:

Leo asked: "Also, do I remember correctly that 'fox hole' perforations have right-angled corners whereas conventional release print perfs have rounded corners?"

For film perforated KS, standard SMPTE 139 specifies the radius of the perforation fillet (corners) to be 0.020 inches (0.51mm).

For film perforated CS, standard SMPTE 102 specifies the radius of the perforation fillet (corners) to be 0.013 inches (0.33mm).

Posted by Paul Mayer (Member # 355) on 05-25-2002, 03:28 PM:

Digging up this old thread for a hypothetical question:

Let's say you're occasionally running vintage 4-track mag prints and you've gone to the trouble of obtaining CS sprockets. What are the potential pitfalls of running everything on CS once those sprockets are installed? Or is it better/necessary to switch back to KS or VKF when not running CS perforated prints?

Regards,

Paul
Hoping/Hopping for a walking cast on June 5th...
Crown Theatres Neonopolis 14
Sin City, NV USA

Posted by Gordon McLeod (Member # 33) on 05-25-2002, 06:41 PM:

No problems with CS sprockets and standard prints

Posted by Frank Angel (Member # 248) on 05-26-2002, 03:49 PM:

Wow, Mark...THANK YOU! I thought perhaps I had imagined it -- I remember hearing the very same thing, that, dispite what first glance logic might say to the contrary, Foxholes ARE stronger and less suceptible to damage than standard sprocket holes. I've mentioned this to a number of film techies who insist that the opposite is true -- everyone seems to think they are weaker and more problematic. I seem to recall that the article was based on some extensive testing that was done at the time. I run LOTS of mag prints and the fox sprocket holes seem to show no more damage than standard -- and remember, any mag prints that you get now have to be decades old.

And Joe B., that's our form. If you like, I can send you a blank to copy. We've in the process of changing a few things -- adding a space to indicate if the DTS discs were incluced with the print. If you don't run retrospective, you probably can get rid of some of the condition lines for the reels -- I settled on 12 reels because we routinely run MY FAIR LADY and it has 12 reels. You can probably use 8 and it would cover most current features.

Email your mailing address to me and I'll send one out to you. Use Angel@BrooklynCenterCinema.com