by John Sirett
SOME BACKGROUND TO TELECINE
There are, loosely speaking, three classes of Telecine Transfer which I will describe, for the want of better names, as follows:-
(1) Fully Professional :
Top of the range, involving very expensive specialised equipment like the "Rank Transfer", computerised "Flying Spot Scanning" of individual film frames, "Wet Gate" techniques to disguise film scratching, extensive electronic picture corrections and etc.
Video laboratories having this equipment offer their services to the public at a hefty hourly rate.
( Video 8 Broadcast in Artarmon have the 'Rank Cintel 3' machine. Their charge rate is, or was, from about $250 per hour lab working time, -- not film running time)
(2) Semi-Professional methods :
(a) Involving direct optical viewing of the film frame with special and/or supplementary lenses attached to a camcorder focussed directly on the film in the projector's gate. (This method requires re-working of the projector's lamp installation) Can be done as a DIY project, but not easily. I tried, but could not make it work with the close-up lenses I have.
(b) Dedicated "Telecine" machines operating on the same principle as in (a) and made specifically for the purpose. I have not used one of these, but I have seen the resulting video which can be very good indeed.
(For anyone interested, models I see mentioned on the internet are : PanasonicWV-J20N, Goko TC-20, Elmo TRV-S8, Fumeo 9131, Sony BM2100. Ballpark prices range from us$500 to us$1500 on E-Bay.)
(3) The D.I.Y. methods :
(a) Using a small box called a "TELECINE CONVERTER" having a lens, a front-silvered mirror and a ground glass screen. You play the projector into the lens of the box and focus the picture on the small ground glass screen. Then record with your camcorder focussed on this screen.
I tried one of these some years ago and found it quite useless. The small ground glass screen is too refractive, making it impossible to obtain a clear, sharp image. (They cost about $50 to $80 as I recall)
(b) THE "OPTICAL SCREEN" METHOD, which anyone can do, and being a DIY enthusiast myself, the method I adopted.
The basic principle involves simply playing your projector picture on to a suitable screen and at the right speed, then recording it off that screen with your video camcorder, for future showing or for subsequent video editing.
Simple, isn't it !
DIY TELECINE TRANSFER BASICS
(For Super 8 silent film) (PAL System)
MEETING THE SYSTEMS SPECIFICATIONS
There are two major requirements that must be considered:-
(1) One involves elimination of the objectionable pulsating 'flicker' that is so often seen to accompany a telecine transfer. This is of paramount importance.
(2) The other is how to manage the difference of frame rates (frames per second) between the original film and the television system.
ELIMINATION OF FLICKER
The pulsating "flicker" I refer to, is caused by a variation in the exposure times of successive video frames recorded by the video camera. This occurs when the projector is "out of phase" with the TV system.In the PAL system, video operates at 25 frames per second while super 8 silent film is shot at 18 fps.
NB: Interestingly, this flicker is not caused by a conflict between frame rate and cycles per second of the electricity supply (50Hz) to the projector lamp. (Even if a direct current supply is used to power the projection lamp, the flickering still persists unchanged. I tried this.)
The power supply alternations (Hz) sets the timing of the TV fields and frames. Every other operation of telecine has to comply with this. So in the PAL TV system we have 50 fields and 25 frames per second
THE THEORY OF TELECINE "PHASING"
Using a film projector with a 3-bladed shutter (the most common), each film frame is projected on to the screen at three equal intervals of time (I call them 'flicks') before the film advances.
In the case of Super 8 film, recorded at 18 frames per second, each of these exposures (flicks) is about 1/108th sec each in duration (Total exposure time then, is: 3 x 1/108 = 1/36th second for each film frame).
Between each individual 'flick' exposure (1/108th sec) there is an equal amount of time where the shutter is covering the film gate and light cannot pass to the camcorder.
So, 6 x 1/108th sec = 1/18th second = one film frame's time in the gate.
Now, if a projector is "out of phase" with the camcorder, it will happen that every so often (and repeatedly), that the camera will be unable to receive the 'total exposure time' of each film frame, (1/36th sec from the projector), due to projector shutter action not synchronizing with the change of video frame .
Notice in the diagram that the change of film frame does not coincide with the change of video frame. The amount of light received by the camcorder therefore, is continually varying on a regular basis.
These exposure variations occur too rapidly for the camcorder's auto-exposure to adjust and so a visible, pulsating "flicker" becomes noticeable.
TWO POINTS OF IMPORTANCE EMERGE AT THIS TIME :
Firstly, it is the projector frame rate that has to change to get "into phase" with the camcorder.
Secondly, a manual adjustment of the camcorder exposure will not overcome 'flicker' because it cannot correct the out of phase condition. It will still occur even when a different exposure time is set on the camcorder. (I use my camcorder exposure simply set to Auto.)
HOW TO GET "INTO PHASE"
The formula is this :
To achieve correct phasing, the total number of projector exposures (flicks) per second, must be wholly divisible into the number of TV frames per second, or a multiple of those TV frames per second.
This is usually referred to as "the number of blades on the shutter, times the number of frames per second, must divide evenly into the TV frames per second, or a multiple thereof"
(Multiples of PAL TV being 25, 50, 75, 100, etc)
TRANSFERRING 18 fps FILM (Super 8 silent) TO PAL.
To get 'into phase', according to the formula, it is necessary to slow the projector down to 16 2/3 fps.
Therefore, a projector with variable speed control is essential
With a 3 bladed shutter (the most common):--- 16 2/3 x 3 = 50 'flicks' per sec, and is wholly divisible
by 25. So no flicker results.
Notice that exactly two film frames fills three video frames consistently along the time line. In this way there will be no exposure variations caused in the camcorder.
Now,18 fps reduced to 16 2/3 fps is a realtime speed reduction of 7.2%, a fairly considerable amount. Will it be noticeable ? Will it be visually acceptable ?
A 'Rule of Thumb' regarding visual perception :
"You are observing two moving objects without the benefit of measuring equipment or instruments. If you can detect, with the naked eye, that one is moving faster than the other, then the difference in their speeds will be 10% or more.
Conversely, if you can't detect any difference, it will be less than 10%."
Applying this rule to telecine, the above Super 8 transfer would seem to be acceptable, running 7.2% slower than normal. However if it is not acceptable, because motion looks jerky, speed adjustment can be made on a computer editing program to restore correct 'realtime' speed. But that is another subject.
On the other hand if we simply speed up 18fps to 25 fps there will be a realtime speed increase of 13.8% which is noticeable and not acceptable - I have tried it. ( I call it "The Charlie Chaplain effect"!)
ABOUT THE DIFFERENCE IN NUMBER of FRAMES PER SECOND
Because the ratio of 16 2/3 to 25 is exactly 2 film frames to 3 video frames, every third video frame will carry an image mixing two film frames. This is unavoidable. It looks dreadful when you inspect your video, a frame at a time, but when it is being played on the TV screen the "dual image" just behaves the same way as adjoining frames do normally.
TRANSFERRING STANDARD 8 (and others filmed at 16 fps) TO PAL
Increase the projector speed to 16 2/3 fps to eliminate flicker, (a 3.75% realtime speed increase.)
The ratio of frames is then same as in the super 8 example.