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February 2005, Week 4

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Subject:
From:
Leo Enticknap <[log in to unmask]>
Reply To:
Film and TV Studies Discussion List <[log in to unmask]>
Date:
Thu, 24 Feb 2005 18:54:17 +0000
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Jesse Kalin writes:

>The background "flashing" (or flickering of light-darker-lighter...) seems 
>ubiquitous in silent films as we see them today, even when well 
>remastered.  Is this an artifact of the originals, deterioration of the 
>film stock, producing copies, ...?

Given that most studio cameras were hand-cranked until the conversion to 
sound, there was sometimes a variation in exposure length between each 
frame, especially at lower speeds (Griffith films shot by G.W. 'Billy' 
Bitzer using the Path้ camera are a case in point).  Most visible flicker, 
however, is not so much an artifact of the originals but of the way they 
are seen, either through a film projector or the telecine (film to video 
copying) process.  Before going any further we need to get to grips with 
how the illusion of movement is created in film projection.  Stephen 
Herbert's essay at www.grand-illusions.com/percept.htm is a good place to 
start, as is Joseph & Barbara Anderson, 'Motion Perception in Motion 
Pictures' in Heath & De Lauretis (eds.), 'The Cinematic Apparatus' 
(Basingstoke, 1981), pp. 76-95.

That lot having been digested, around 45-50 shutter movements per second is 
generally considered about the minimum needed to produce the flicker-free 
image of continuous movement using a conventional film projectors.  Until 
the 1920s most had three-blade shutters, that is to say a disc of metal 
with three holes cut in it, between the light source and the screen.  Each 
time the third blade blocked the light source, the projector's intermittent 
mechanism pulled down a frame.  3 x 16 = 48, therefore a shooting rate of 
16fps was generally considered the minimum needed for the accurate 
reproduction of movement in projector.

During the 1920s projector manufacturers gradually moved from three to two 
blade shutters: the former absorbed more light, and the picture palaces 
springing up with 1,000 seats or more and a long throw from projector to 
screen needed all the light from their projectors they can get.  If you 
fall below those 45-50 shutter movements per second, you see a flicker.  So 
projection speeds in cinemas increased because of the two-blade shutters, 
as a result of which studios were effectively forced to increase shooting 
speeds.  When 24fps was standardised for sound on film, the main reason was 
that this was what most theatres were doing anyway.

Show a film significantly under 24fps with a two-blade shutter and you'll 
see a visible flicker.  For this reason arthouse and rep theatres which 
regularly screen silent prints normally fit three-bladed shutters to their 
projectors.  But somewhere which shows the occasional one-off silent, or a 
16mm print shown on a portable projector in a classroom, probably won't do.

There were similar problems with video transfers.  Telecine equipment 
designed for the PAL system (50hz) normally runs at 25fps and simply scans 
each frame (both fields) twice.  For NTSC (60hz) the so-called 3:2:2 
pulldown is used, whereby some fields are scanned more often than others in 
order to fit 60hz (which would be 30fps, i.e. too fast to get away with, if 
you scanned each frame twice) into 24fps.  Nowadays, computer-controlled 
telecine and datacine equipment can transfer film at whatever speed and 
into whatever system you like, but this wasn't the case until the early 
'90s or so: before then, transferring at non-standard speeds also did nasty 
things to the resulting image on the tape.  For more on this see 
Kallenberger & Cvjetnacanin, 'Film into Video: A Guide to Merging the Two 
Technologies' (Focal Press).

A monumentally shameless plug: this and other related issues are covered in 
my book 'Moving Image Technology: From Zoetrope to Digital', published by 
Wallflower Press in April (US distribution from June: 
http://www.columbia.edu/cu/cup/catalog/data/190476/190476407X.HTM); though 
admittedly in nothing like as much depth as in the work cited above.

So the short answer to your question is that in most cases, where flicker 
is visible on a silent film viewed today, the equipment used to view it is 
usually responsible: but not always or entirely.  Until the conversion to 
sound there was no standardised shooting or projection speed, with the 
result that chaos reigned.

Leo

P.S. Many thanks to all who answered my 'Big Sleep' query.  Affect it is, 
by the looks of things.  Having rechecked both definitions in Chambers, I 
suspect that the many and often very subtle differences between US and 
British English could have had something to do with my confusion.   

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