Questions about Telecine Frame Rate Capabilities and 3:2 Pulldown

[Karl Lee]

As I've been reading about the finer points of telecine transfers and 3:2 pulldown, more and more questions have been coming to mind regarding frame rates and the capabilities of telecine equipment, so hopefully someone can help clarify a few of my questions. (and while it's probably implied, it's worth mentioning that the frame rates in my post are all based on 60 Hz North American systems.)

 

Although a vast majority of telecine transfers are done at 24 FPS, I had always been under the impression that telecine machines are capable of transferring film at any desired frame rate. However, now that I'm starting to understand the mechanics behind film to video telecine transfers, I'm not so sure that this is the case. On account of having to adhere to the 24 FPS frame rate for achieving 3:2 pulldown, are most telecines limited to transferring film at 24 FPS (well, actually 23.976 FPS) or any multiple thereof, or 30 FPS transfers (actually 29.97 FPS) or any multiple thereof? I assume a 29.97 FPS transfer would technically be the easiest since it matches the video frame rate exactly and probably wouldn't require any special interlacing or pulldown processing. Or, do telecines have various types of internal interlacing algorithms that permit telecine transfers at virtually any frame rate?

 

Also, while telecine transfers commonly referred to as "24 FPS" are actually performed at 23.976 FPS, has it ever been common practice for cinematographers to film at 23.976 FPS instead of 24 FPS, provided their camera is capable of such a precise frame rate? I realize that the difference between 24 and 23.976 FPS is extremely negligible...it's only a 1/1000 reduction in speed, which amounts to about an increase of 3.6 seconds in play time over a period of 1 hour. However, in terms of visual appearance and syncing with audio for shorter scenes, I'm curious if any cinematographers have done so, especially if a project is destined for 24 FPS (actually 23.976 FPS) telecine transfer.

 

Finally, taking into consideration telecine judder and the visual effects of 3:2 pulldown, has filming at 30 FPS (or 29.976 FPS to accurately match the video frame rate) ever been considered as a way to improve the quality of a film project destined for telecine transfer, considering that it would provide a true 1:1 frame rate ratio for the telecine transfer? Aside from the obvious consequence of burning through film a little more quickly at 30 FPS than 24 FPS, would film shot and transferred at 30 FPS still maintain some of the overall appearance of film but have more of a video-esque appearance in terms of motion?

 

Lots of questions floating around in this post...I know :) Thanks to anyone who's made it this far and might be able to answer some of my questions!

[David Mullen ASC]

Most film is shot at 24 fps. It is transferred to video at 23.976 fps in the U.S. because video plays back at 29.97fps/59.94i with a 3:2 pulldown. No one can see the difference between 23.976 fps and 24 fps.

 

Trouble with actually shooting at 29.97 fps for a frame to frame transfer to 59.94i video to avoid a 3:2 pulldown is that some projects also get shown in 50Hz countries, and it is easier to transfer 24 fps (or 23.976 fps) movies to both 59.94i and 50i than it is to convert 29.97 fps to 50i. At the simplest method, you just run 24 fps material at 25 fps in the telecine to make a 50i version. So 24 and 25 convert into 50 easier than 30 does.

 

Plus people are used to theatrical movies shown on U.S. television to have a 3:2 pulldown -- 30P video sometimes looks a bit, well, video-ish because of the smoother motion. If you look at the DVD of "Oklahoma!" you can get a slight sense of that since it was shot at 30 fps 65mm (and 24 fps 35mm). A few TV shows and commercials have shot at 30P to avoid 3:2 pulldown but the general consensus is that things look more like classic movies in terms of motion if shot at 24 fps.

 

You would generally transfer to video at the shooting frame rate so that the sound would be in sync, so if you shot at 24 fps, there isn't much reason to transfer it at 29.97 fps just to avoid a 3:2 pulldown unless the material is destined for video effects work (hopefully MOS footage). But in this day and age, it is more likely to scan film negative to RGB DPX files for effects work anyway and not record to a video codec.

 

Most digital cameras shooting for cinema and narrative TV shoot at 23.976P in the U.S. Mainly because most sound post paths are used to working with video copies that are running at 59.94i. If the final master will be shown at true 24P, then the audio sync is adjusted after the final mix for that version.

 

Also, these days there is no reason why you have to telecine transfer to 59.94i, that's just one of many display options for mastering. But it is possible to scan whole frames and work at 24P (or 23.976P) for most of post.