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WHEN TWO (OR THREE) IS BETTER THAT FIVE!

The ABC news had just started and our phone rang, the person on the other end
asked “Is that the bloke who puts out a book on filums?” I guess I roughly fall into
that description, so I said “yes”. The follow up question was “do you have a 16mm
projector with a five blade shutter for sale”. I said “no, why do you want a
projector with a five blade shutter”. I was then told quite bluntly that “everyone
knows you need a five blade shutter to copy films to DVD”. When I replied “Not
with the Australian TV system”. I was basically told that I didn’t know what I was
talking about and he was wasting his time talking to me about it. That was followed
by a click and the conversation was all over in less than sixty seconds.

I have no idea who the person was that called, but with his abruptness and general
lack of basic courtesy, I hope he wasn’t a Reel Deals subscriber. If the
conversation had gone on much longer, he would have been told just where he
could put his five blade shutter!

Over the years this same topic has been raised and the same question asked of me
a few times, so here goes!
What is this five blade shutter business all about?
It all comes about because of the different TV systems used here and in the
USA. Our system (PAL) uses a 50hz frame rate (same as our AC mains frequency),
whilst the USA TV system utilises a 60 Hz system.

With the Internet being the main ‘book of knowledge’ for many people,
information specific to the United States gets an airing world wide. Many
American contributors may be unaware that there are other TV systems in the
world, beside their NTSC 60hz system.
When transferring film to TV, to prevent flicker, the film projection speed
(Frames per Second) should be the same or a sub-multiple of the TV camera scan
rate. So with a TV scan frequency of 50hz, running the projector at 25 FPS with a
standard two blade shutter the light from the projector will be interrupted
(flicker rate) 50 times for second, equalling the TV scan frequency and no flicker
will result. The increase in speed from 24 to 25 FPS (4%) is generally not
noticeable to all but the music purists who can pick the slight increase in pitch.

At 24FPS, a strobe effect in the picture will be quite noticeable on most scenes,
resulting in a dark bar travelling down the screen. It should also be said at this
point that if the projector has a three blade shutter (this is particularly the case
with 8mm machines, as they are designed to run at both silent and sound speed,
the three blade being necessary to eliminate flicker at 18FPS), running it at 24 or
Reel Deals - 10 - June 2014