7.0 Questions on 70mm Projection!
The 70mm Newsletter
by: Duncan McGregor
23 August 2006
"What should a 35mm projectionist new to 70mm look out for?"
Answer: The obvious one is the fact that you are dealing
with a larger format, so more care should always be applied
at all times when handling this film gauge. Also if a
projectionist is new to the format for the first time, then
it’s essential they are given training by a qualified
professional before attempting to handle it, as it is
markedly different from 35mm.
The other major difference is the bigger frame which is 5
perforations high, as opposed to 4 perforations for 35mm.
Until recently all 70mm prints had magnetic striping for
sound reproduction, but with the advent of DTS a major
difference is now noted in the projection room, as the film
runs through the projector more quietly and there is visibly
much less dirt and deposit to clean on the projector, as a
result of oxide no longer peeling from the magnetic tracks.
The speed is 112,5 feet per minute, so tab cues and
automation mark placements will be different.
Another major difference owing to the larger gauge is the
overall weight of a 70mm print or individual reel, so it is
advisable to use trolleys, hoists or mechanical aids where
available, to avoid excessive lifting and potential injury
to ones self.
"Tell us about de-gaussing issues when screening 70mm
Answer: With the passage of time and less attention paid to
magnetic sound heads in projection rooms, there has been a
small but significant increase in the amount of magnetic
prints suffering from contamination, with regard noise
interference of one or more tracks becoming “magged up”. The
result is an annoying click or crackle on the track, which
is impossible to remove once there. Unplugging the offending
speaker or switching the appropriate amplifier off is the
only solution. Therefore careful use of a demagnetiser
across the sound head can help reduce this occurring. The
damage usually occurs via other metal parts on the projector
that the film comes into contact with such as rollers,
sprockets and spindle shafts etc., so these should be
demagnetised frequently as well. It’s therefore important
that all parts of the film path from the platter if used are
checked, that could cause this problem. However, proper
training in the use of degaussing equipment is essential
otherwise you can make the problem worse.
"What tips do you have when operating DTS-70? For instance,
we have heard the Reader must be exactly aligned each time
to cater for slightly different timecode track positions".
Answer: I’ve only ever been aware of the time code being
placed in a different position to normal for DTS-70 on one
occasion. This was when we screened "Independence Day"
(ID4),’ therefore we had to borrow the alternative reader
from DTS in order to enable this. Other than that the time
code is always in the same place, so no adjustments should
really be necessary, though a yearly service by qualified
engineers is always helpful, to check and test out the
various sound systems.
The key change that needs to be remembered is altering the
time code offset from 35 to 70mm. This will also need
amending if the print is shown at 30fps and if the sound has
been authentically restored from original 6 channel mixes
utilising the full compliment of 5 stage speakers (commonly
referred to as special venue 6 channel), then the correct
DTS processor is vital and some method for switching between
5.1 and special venue is essential.
As the digital readers all use red LED’s, then some of these
can fail from time to time and need replacing. Also if the
voltage output of the LED’s falls below its required
minimum, this will also result in problems with reading the
"Any special advice on make-up and break-down procedures?"
Brown and Tony Cutts. Image by Thomas Hauerslev
Answer: When making up 70mm prints, as much time as possible
should be allowed to do this, as it takes time to adjust to
its different size, feel and texture. Check each reel
individually and make up the entire print, before assembling
onto a plate machine for example. Always avoid visibly
marking the print or reel edges with chinagraph pencil (as
over time this will flake and contaminate the picture area).
Similarly do not apply coloured insulation or masking tape
etc to help identify reel changes. This is bad practice and
needs stamping out. Also if doing reel change-overs, only
use recognised cue dot markers. It is frustrating and
annoying when older prints have several cue dots scratched
on the ends of all reels, which visibly detracts from the
Be sure to identify the correct ratio and sound format as
there can be many options. With regard sound it’s vital the
right format is selected. Up until the early '70s all prints
were non-Dolby encoded – Format 40. With the introduction of
Dolby encoded magnetic tracks there are two primary formats
– 42 for standard Dolby and 43 for split surround. If the
print has been equalised for SR reproduction, then
appropriate sound cards need installing in the processor
beforehand and Format 41 selecting to correspond.
When spooling off all leaders and tails should be attached
correctly to the appropriate reel. An increasing number of
occurrences continue to happen with leaders and tails
attached to the wrong reels. This creates confusion and
frustration for the projectionist and adds to the overall
time an operator has to spend on a print when received at
the next venue. Leaders and tails should also be spliced as
normal and never just wrapped round the end of a reel.
As 70mm prints are very rarely printed these days, it’s
vital that all projectionists treat these prints with the
utmost care and respect, as replacement copies in the
majority of cases are simply unavailable, so careful
handling will help prolong the lifespan of this superior
"How does tape splicing on 70mm differ from 35mm?"
Answer: There is no real major difference with tape
splicing, however butt splices should always be applied and
made, and overlap joins avoided at all costs. Overlap joins
are noisier, less flexible and more open to jumping in the
gate. Also half inch wide tape or less is better for
providing a smoother, quieter splice. Narrower tape also
means that less of the magnetic track is covered which
affects sound playback. Ideally the splice that covers the
magnetic tracks should be trimmed so as not to cover them,
using the template provided with some 70mm splicers.
"Tell us something about changing from 35mm to 70mm on dual
gauge machines, e.g. changing the gate, sprockets and pads,
and installing a beam spreader?"
Answer: Each make of projector is unique to itself, so
practices will differ slightly. On a Cinemeccanica Victoria
8 projector, when changing from 35 to 70mm, you turn the pad
roller round on its shaft. With a DP70 projector, you change
the entire pad roller assembly. Heat shields may need to be
removed and aperture plates and lenses have to be changed,
as do the front and rear gate assemblies. Most 35/70
machines usually have dual purpose top and bottom sprockets,
so these don’t have to be touched. However the intermittent
sprocket usually does and it’s important that these are
lined up and fitted correctly. Therefore read the manual
relevant to your own projector and follow it carefully.
Some projectionists forget to change the odd pad roller and
this is where annoying, visible parallel scratches appear
35mm apart, running throughout the entire print if it has
occurred operating from a plate machine, or on alternate
parts if shown with reel changeovers.
The beam spreader acts for light in a similar way to an
anamorphic lens affecting the picture. It enables the spread
of light horizontally to fill the 70mm aperture. Refer to
your lamp house manual for installation instructions, but if
it is put in the wrong way up, it will leave dark sides. The
majority can be turned in their bracket in order to set them
up correctly. The xenon lamp will need refocusing anyway to
fill the aperture and this is best done with a white light
on screen, so you can be sure of obtaining a uniform, even
"How do you think technical procedures for screening 5/70
prints could be improved?"
Answer: If theatres are afforded the time to test run 70mm
prints, then the majority of technical issues can usually be
identified and ironed out beforehand, should they exist. A
clean, tidy, well organised projection room will always
benefit the projectionist and general smooth running of any
show. Maintenance standards though need to be considerably
higher where 70mm is in operation.
There was never any standard sound level for magnetic
prints, so each cinema needs to determine its own for every
print that is shown, so it is best to run at least one reel
if time allows. To help with this, from the '70s onwards,
the majority of prints were released with a Dolby tone (and
sometimes pink noise). This enabled the projectionist to run
the tone and tweak the magnetic preamps to balance the
channels for each film.
Always check the film path through the projector when
screening 70mm to be sure it is running free and clear of
any obstructions. It is all too easy to be over confident
and overlook obvious, potential pitfalls. Likewise check the
film path from and back to the plate machine.
Overtures, Play Ins, Play Outs and Intermissions should
never be cut out of any print. They are there for specific
reasons and aid greatly the majesty, grandeur and “road
show” style presentations of such films. It is one thing to
have an overture or play in cut out, which is there to build
and create atmosphere for what is to follow, but deleting an
intermission can often be disastrous. Intermissions are
there more than just to aid the selling of popcorn – they
often show the passage of time. For example in "El Cid" with
the intermission cut out, this shows Charlton Heston change
from a very young man to an old, bearded man in a split
second. This confuses the audience, whereby they think part
of the film has been cut, which of course it has – the
in 70mm reading:
Advanced Projection Manual is designed to
provide cinema engineers and projectionists with the
necessary technical know-how and hands-on advice so
that classic films can be presented the way they
were intended to be presented
70mm 5-perf cinemas outside North America
5-perf cinemas in North America
The 65/70mm Workshop extends its grateful thanks to Tony
Cutts, Dick Vaughan and Symon Culpan of The
National Museum of Photography, Film and Television,
Pictureville, Bradford for their contributions to this
More on 70mm Film Handling...
65/70mm workshop is grateful to also be able to publish this extract from
Advanced Projection Manual by Torkell
General guidelines with regard to 35mm film handling naturally also apply to
70mm film. However, additional precautions should also be taken.
Most 70mm film prints have magnetic sound tracks (indeed, virtually all
prints do except very recent restorations or new films with the DTS time
code for digital sound playback based on CD-ROM). These tracks, though more
rugged than common belief would indicate, are sensitive to de-magnetisation.
Any magnetic fields from motors, transformers, etc., have the potential to
ruin the magnetic sound tracks, as do permanent magnets, including tools,
scissors or parts made of magnetisable metals (steel, iron) that have been
magnetised. 70mm film prints should never be kept or stored close to such
Furthermore, any parts of the rewind bench, the projector or the splicer
which touch the film should be de-magnetised (degaussed) by a degaussing
tool before 70mm film is handled. There are two types of degaussing tools
available. The most commonly used is the "iron-type" tool suitable for
degaussing small metal parts such as screws, shafts, sprockets, splicer
knives etc. The other is the much bigger "coil-type", suitable for
degaussing substantially bigger items such as the complete projector
mechanism. It should be noted that the degaussing tool itself will ruin the
magnetic tracks if it is close to the film when connected to the mains, so
it is common sense to do the degaussing work prior to bringing any 70mm
prints into the projection room.
Seventy-millimetre film is almost exclusively distributed on spools rather
than bobbins or cores. These spools, though compliant with most projector
film transport systems, are intended for transport only. Because of rough
handling in transit, most transport spools have severe dents or bent reel
flanges. Also, transport spools are typically made slightly narrower than
projection spools, as their main objective is to keep the film in place in
transit. When used for projection, such spools have the potential to do
severe damage to the film, both to the carrier base and to the sensitive
magnetic sound tracks. When a 70mm film is prepared for projection, it
should therefore be wound from the transport spools onto the cinema's own
70mm projection spools. When winding the film from the transport spool, it
is strongly recommended that the winding is done very gently and that the
film is slightly tilted by hand (holding only the edges) to prevent it from
catching on any dents in the flanges of the transport spool.
Another must is to ensure that the leaders are in good shape and of
sufficient length. Because of the higher torque required to transport 70mm
film (particualrly during acceleration), any minor perforation damage, poor
splices, etc., could well cause problems during the start sequence of the
reel. Though expensive, new 70mm leaders should be kept at hand and used
whenever there is any doubt that the existing leader can cope. After all, it
is a small investment if you consider it will not only ensure that
performances go ahead smoothly, but will also protect the quality of very
rare and expensive 70mm projection prints.
Reproduced by kind permission of the Author
(c) 2006 Torkell Saetervadet, The Norweigian Film Institute - Oslo and The
International Federation of Film Archives (FIAF) - Brussels
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