24 to 30 Frames Per Second
The Actual Relationship
One of the greatest mysteries of the relationship of film and video is about to be revealed.  There are always discussions concerning the exact relationship between the two frame rates and a great deal of the time, the topic is misunderstood.
There are basically only a few different issues on the topic to understand.
 
The first rule is:
WHEN I SAY 30 I MEAN 29.9

1.  A conventional telecine is basically a projector that is aimed at a camera.  This device is sometimes called a "film chain".  The most popular of these was the RCA TK-27 and TK-28. When I first started working in television, we ran all of our commercials on film.  For more on this, check out my "working in broadcasting" pages.  In any event, the telecine chain enabled the use of multiple projectors, usually two 16mm film and one 35mm slide projector, on a single camera.  The chain is facilitated by means of a multiplexor which is a series of mechanically operated mirrors used to direct the appropriate My friend Koz has written a pretty good example of what really goes on.  Basically, the relationship between the film speed and the video speed is not necessarily locked.  The projector motor may be locked to the video sync, but often, and originally, the projector motor was a simple AC synchronous motor.  The telecine shutter does enough flashing that the tube based telecine camera thinks the image is there all the time.  There is an activity everyone calls three/two that really makes everything happen.  Koz's example is something that I cannot improve on.

2.  The modern telecine, usually the Rank, is completely different than the conventional telecine.  The Rank operates with a device called a flying spot scanner.  There is the CCD type telecine.  Bosch makes the most popular version of this device.  The 3/2 action that is used here is more precise.  The film runs at an exact  5/4 relationship.  Basically if you want the film to work correctly when recorded on video, the projector must run at 23.9 so there is an exact relationship.  The 3/2 is done by using digital memory and benefits from the fact that the video is really running at 60 fields per second as compared to the film running at 24.  Again, Koz explains this the best.

3.  The hardest thing to understand, and the least known about, is what happens when you film off of a monitor.  This will be the longest explanation.

The first thing you have to do is get your camera running at an exact speed that is locked to the video.  Since the video is running at 29.9 the film camera must run at 23.9.

 
Now it is time to look at the illustration.
 
The top row contains the video frames and the bottom row contains the film frames. The shaded area is exactly 1/2 or 50% of the film frame.  This illustrates the portion of the film camera time that the shutter is closed.  Therefore, the white area of the bottom row is the actual time that the film is exposing.

From this diagram, you can easily see that the camera will only expose slightly over 1/2 of the 1st. video frame.  The shutter then closes until a little over 1/4 of the 2nd video frame where it starts exposing again.  Again and again, until at the end of video frame 5 and film frame 4 everything lines up again.

When you film a monitor in this fashion, the video will appear to have a dark bar rolling through it.  The bar will make a complete cycle 6 times a second.

Understanding this process will be the basis for completely understanding the 144 degree filming process as well as the 24-frame video process.  Its all about things happening in sequence over time.

 
 
 
Here is the same illustration from above shown against above a similar illustration.  The big difference here is that the lower illustration is a system using a 144 degree camera shutter and the upper illustration uses a 180 degree shutter.
 
SOME FACTS TO KEEP IN MIND
    1. At 24 fps when using a 160 degree shutter, the exposure time is 1/48th of a second.
    2. At 24 fps when using a 144 degree shutter, the exposure time is 1/60th of a second.
    3. Video at 30 fps (29.9) will display a complete field (1/2 of a frame) in 1/60th of a second.
     
Now, here goes...  You can see that the camera will expose a complete video field then the shutter goes dark for the second field of video frame 1 and about 1/2 way through the first field of video frame 2.  Then the camera exposes for another 1/60th of a second.  This second film frame gets the second half the first field of video frame 2 through the first half of the second field of video frame 2.  Do I have to do them all?

The whole process takes 4 film frames or 5 video frames then starts all over again.