[Tig] 16fps Film Transferred on Rank Cintel & Pulldown

Gary Adams garyada at ix.netcom.com
Fri Oct 22 15:34:45 BST 2010


Hello John.  I can offer some information here.  As far as I know, most, if not all telecines are not capable of a "locked" sequence when transferring any speeds other than 23.98 and 29.97 in 525 worlds, as well as 25.00 in 625 worlds.  Later URSA telecines were designed with a "locked" sequence when running at 24 fps in a 25fps video standard.  In the URSA handbook, the sequences were described for various frame rates but they were not guaranteed.  So while most of any given sequence would indeed follow the exact sequence, there would be the occasional added or missing field to make up any long term variation of the linear film speed with respect to the video output.  

If you consider film running at 15fps, you would need exactly 2 video frames (4 fields) for a given film frame in a 30 frame video standard.  So with film running at 16 frames per second, we need room for one whole film frame every second.  This would mean dropping 4 video fields out of the sequence every second to make room for the extra frame.  Since there are 60 video fields in the video second, the sequence would look something like:

15fps second:  	4:4:4:4:4:4:4:4:4:4:4:4:4:4:4
16fps second:	3:4:4:4:3:4:4:4:3:4:4:4:3:4:4:4

So indeed the sequence would be 3:4:4:4 as you have found.  You can verify this by stepping through the frames of your video where there is obvious motion and count the fields of four successive film frames. 

I would say you will find this sequence to be fairly good for the most part but realize each time the telecine is started, the sequence will start randomly, and the exact speed of the telecine is not guaranteed to be 16fps.  In fact in a 59.94 world, it will be slightly lower than that anyway, but over the long term, the sequence will drift a bit.

Sorry to be so detailed here.  It's an important problem for archivists since they wish to recreate as best they can the original film speeds in a digital world and it is not easy.  If you are going to work on films that are not our traditional locked speeds, it is best to transfer in a 1:1 mode and post process the film speed.  Then we get into looking at all of this on a digital display which is greatly off topic.

Best Regards, Gary Adams
Former TLC Product Manager
Now Revival Product Manager
Blackmagic Design



-----Original Message-----
From: tig-bounces at colorist.org [mailto:tig-bounces at colorist.org] On Behalf Of John A. Mozzer
Sent: Friday, October 22, 2010 1:41 AM
To: tig at colorist.org
Subject: [Tig] 16fps Film Transferred on Rank Cintel & Pulldown

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First, I'll reintroduce myself.  I am not a professional in this field, 
and am not affiliated with any company or service.  Over a year ago, I 
had about ten hours of silent regular 8mm films transferred to MiniDV 
tapes via Rank Cintel, using a service.

The technician has been using a regular 8mm film gate on the Rank for 
many years.  The films he transferred for me are 16fps. I spoke to the 
technician several days ago to ask about the pulldown used. He preferred 
the term "sequence", because the Rank doesn't use claws to literally 
pull down the film. He said the Rank, "multipulses to slow the film down 
to the correct speed." He didn't know the sequence exactly, though, 
because the Rank does it automatically.

Could any of you tell me the likely pulldown?  I mean, please express it 
similarly to the way pulldown for 24fps is often expressed as 2:3:2:3.

I now have all this DV footage in Final Cut Express, and I wonder what 
might happen if I deinterlace.  To complicate things further, the 
technician explained his "controlled one light" service sometimes 
involves stopping the process in order to fix levels, and starting 
again. I believe it, because when checking all of the transfers, I never 
saw an "on the fly" correction during a scene. But this also means the 
"sequence", or pulldown (we can call it that, I guess), changed every 
time he did such an edit.  I can use DV Start/Stop Detect in Final Cut 
to easily find these edit, I believe.

While the web is filled with explanations about the pulldown for 24fps, 
I found only one article explaining that pulldown for 16fps is 3:4:4:4. 
  But that article was not about the Rank Cintel.

John A. Mozzer
Los Angeles, CA

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