Filtration Techniques

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Filtration Techniques

• Or
• How to print four different soundtracks
• Onto one piece of film
• To three different densities

Andrew Wales Technicolor London.
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From Negative to Print
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Factors affecting print density

• Sound negative type - (Base Density)
• Print stock
• Soundtrack lamp age
• Filters set up condition
• Trend factors - Unlikely to have sudden
  movement.

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Possible Combinations of Negative type Print
Stock.
Negative Positive Agfa ST8D Kodak
2383 Agfa ST9 Kodak 2393 Agfa CP20 Kodak
2378 Fuji 3519 Kodak 2376 Fuji 3519D (Hi
Con) Kodak 2374 Total of 25 combinations
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Not Forgetting High Magenta!

• Include High Magenta soundtracks and this doubles
  the number of filter packs!
• Therefore, need to optimise so that each filter
  can be used with various combinations of
  negatives and print stocks.

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How to Optimise Printer Packs.

• Each print stock has its own voltage setting so
  that the analogue track is printed to the correct
  density.
• Within the aims set for the digital tracks, print
  a test onto each positive stock and work out an
  average filter pack for the print stocks tested.

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What is a Filter Pack

• Collection of colour correcting filters selected
  so that when printed through the negative, gives
  a print density on aim.

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Filter Pack Examples

• Analogue
• Yellow filter (e.g. Wratten 12) UV filter if
  required.
• Dolby Digital
• Red and yellow CC filters ( neutral density if
  required) to give neutral print density aim.
• Sony SDDS
• Red filter (e.g. Wratten 29 or Agfa L622)
  neutral density filter to give cyan print density
  aim.

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Balancing Digital Print Aims

• The print density aims of the digital soundtracks
  are dependent on the negative density (as for
  analogue tracks), we have found that with
  increasing negative density the print density
  tolerance increases.
• Therefore the higher the negative density the
  more flexibility in filter pack.

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Tolerance of Dolby Digital Soundtracks to print
density variation.
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High Magenta Analogue Tracks.

• Need to control both the infra-red and cyan dye
  densities.
• Done by adding cyan CC filters to the standard
  analogue filter (e.g. Wratten 12)
• Requires careful balance of voltage and cyan
  filtration.
• Like digital tracks, are susceptible to
  variations in base colour of the negative

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Filter Pack Problems

• Problems with filter packs occur when the print
  density falls outside the range over which a good
  QC can be achieved.
• This may be due to the following factors
• Filter fading
• Lamp ageing
• Non standard track negative

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Non Standard Track Negatives

• A Non standard optical negative is one when the
  soundtrack densities fall outside the range where
  good QC results are possible using an optimised
  filter pack.
• Could be caused by
• Soundtrack density being too heavy/light
• Base density of the sound negative stock
• Therefore need to print using a reoptimised
  filter pack

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Filter Packs Made Easy

• Consistent optical negatives
• High density negatives (digital) to ensure wide
  range of print densities available
• Regular replacement of filters to reduce fading
• Minimising the number of individual filters in
  each pack.
• Convert all analogue tracks to High Magenta

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Cyan Dolby Digital Tracks

• Instead of using CC filters to produce a neutral
  print density, use the red filter used for SDDS
  printing ( neutral density filters) to produce a
  cyan Dolby Digital print.
• Allows for reduction of problems regarding
  negative base colour filter fading.

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Summary

• To maintain optimal printing densities, filters
  must be regularly monitored.
• Requires consistent negatives (base track
  densities)
• By increasing digital negative densities,
  maximises print aim window