8mm Forum: That old Coaxial reel debate...again.

This is topic That old Coaxial reel debate...again. in forum 8mm Forum at 8mm Forum.

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Posted by John Yapp (Member # 2873) on January 01, 2014, 10:49 AM:

I would like to defend Eumig's coaxial reel design which seems to be universally disliked. Having owned four different models with this design now, I can honestly say that i am not aware of any damage that has ever been caused to my film due to both reels being at the rear of the projector. On the contrary, Having just acquired a Bolex 715, The equivalent of the Eumig s912, I pushed a test film through it with a very crumpled leader, and quite severe sprocket damage. This film point blank refuses to go through my Eumig 807D, giving up at the first damaged sprocket and ignores any use of the loop reformer, but sailed through the Bolex with one little jump that corrected itself instantly. Admittedly, once the film is threaded, it is pretty much impossible to retrieve, but this is also true of the 800 series as far as I can see. Any thoughts?

Posted by Maurizio Di Cintio (Member # 144) on January 01, 2014, 11:55 AM:

You can't compare the performance of a single toothed claw (like the double gauge 807d's) to those of a double toothed one. In the 807 D claw is single AND very thin so that it can engage the sprockets of both film formats. On the Series 900, instead (and the Bolex 715 is a clone of that) the claw has two teeh AND they are not as slim as in the older model. The better performance you are achivieng with the Bolex depends on this, not on the fact it has no upper sprocket drum. The disadvantage of this reel arrangement is apparent when screening 600' reels and you are approaching the last 4-5 minutes: the unwinding of the film from the feed reel becomes less even, resulting in a slack which is gradually compensated for and then happens again and again: this creates a momentum between feed reel and claw which, at some point, the spring inside the inlet film chute won't compensate for anymore, being too wide. Finally this will result in unsteady images on the screen with the frame line occasinally and regularly becoming visible (usually from the lower side of the screen), something I find rather bothersome and sometimes can lead to perf tear. Hope this helps.

Posted by John Yapp (Member # 2873) on January 01, 2014, 12:05 PM:

A very well reasoned argument Maurizio, and undoubtedly correct. Perhaps it's because I have only one or two 600ft reels that this hadn't occurred to me before. I still think I may give my Bolex a try for telecine work however due to the more stable images on smaller reels. I assume I can achieve the required framerate by slipping the belt onto the 60cycles setting.

Posted by Maurizio Di Cintio (Member # 144) on January 01, 2014, 12:35 PM:

No, it's more simple: remove the black knob for the speed control by pulling it out: this way an exagonal bolt becomes visible, it's white and probably made of nylon; you can turn this nut to fine-adjust the speed and reach 16,66 frames per second. It's very easy, much more than chianging the belt position.

Posted by John Yapp (Member # 2873) on January 01, 2014, 01:20 PM:

Thanks Maurizio, I'll give that a try. Jeez, you Gotta love this forum.

Posted by Paul Adsett (Member # 25) on January 01, 2014, 06:39 PM:

Maurizio has described very well what happens with some 600ft reels on the coaxial Eumigs. I had a 926GL Stereo, and often saw this issue, although not on all 6OO footers. 400ft reels were never a problem.
I eventually designed a bracket with a couple of rollers which mounted on top of the lamphouse. When the film from the feed spool was fed under and over these rollers it really helped to dampen the thrashing and oscillations that Maurizio describes.

I think that the coaxial reels would have worked fine if Eumig had not abandoned the top feed sprocket in place of a flapping roller on a leaf spring.
The 938 had all the great features and performance of the 926GL, plus a normal 2-sprocket film path.

Posted by John Yapp (Member # 2873) on January 01, 2014, 06:50 PM:

that looks a great solution Paul. I had the 936, which was back to the front and back reel configuration, and strangely discarded the optical levelling lens for the more traditional style, yet this made a reappearance on the 938. wonder why?

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