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3.6.1 70mm Standard Frame (Motion Picture Formats - release prints intended for projection)




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This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.

3.6.1 70mm Standard Frame (Motion Picture Formats - release prints intended for projection)

The standard 70mm frame has always has an aspect ratio of 2.2:1, which
is slightly narrower than 35mm CinemaScope (tm) . Often, 70mm blowup
prints were made of 35mm CinemaScope (tm) films (mostly for the
improved sound quality of 6-track magnetic). These blowups are `flat,'
and often provide better image quality due to the superior
registration (image steadiness) of the 70mm format, as well as the
reduced grain imposed by the release print (more grains per square
foot of screen area). This was done more in the past (1970's through
1980's) because the high-quality six-track discrete (as opposed to
matrixed) soundtracks on 70mm prints could not be equaled by 35mm
optical Dolby Stereo (tm) tracks. Several innovations in 35mm,
however, most notably digital sound (along with Dolby (tm) SR, and
reverse-scanning solar cells) rendered 70mm blowups unnecessary if
sound is the only consideration. Further, the recent shift toward
10-20-screen multiplex theaters, and the resultant smaller screens,
has lessened the impact of the larger, better-quality image.

Much of the expense of making 70mm prints in the past has been the
magnetic striping which is necessary for the soundtrack, as there is
no such thing as 70mm optical sound. With the possibility of printing
a DTS (tm) timecode on the 70mm print, and providing the actual
soundtrack on DTS (tm) CD-ROM disks (like with 35mm DTS (tm) ), this
may no longer be necessary, possibly paving the way for a 70mm
revival. This remains to be seen, however, although it was done
successfully for the 70mm release of Hitchcock's Vertigo in October,
1996; the prints had no analog tracks and entire soundtrack was
reproduced from a DTS (tm) disk (most theaters used two disk readers
with identical disks in them for redundancy), driven by DTS (tm)
timecode printed on the outside edge of the perforations on the
left-hand side (relative to how the film runs in the projector) of the
image.

In addition to the conventional sprocket holes, all 70mm prints also
have a small `registration hole' punched every 5 perforations.
Theoretically, this is supposed to line up with the frameline, but, in
practice, this is ignored, and it just occurs at a random point. The
primary purpose served by the registration hole is for use as a
splicing reference, so that splices can always be made at the
frameline, even in the middle of a fadeout or a dark scene.

70mm IMAX (tm) /OMNIMAX (tm) 15-Perf Frame

These special formats are simple contact prints made from the
negatives (or intermediates). Although they are wider (by 5mm) than
the original negatives, they never contain a soundtrack printed
directly on the film. Sound is provided either by a separate,
interlocked magnetic tape, or by a CD-ROM disk, which is driven by a
timecode on the film (as in the DTS (tm) system used for 35mm digital
sound).

70mm standard release print frame:
(courtesy David Richards \texttt{daverich@netcom.com})

  |XXoX|____________________________________|XoXX|
  |XX X|                                    |X XX|  'o' = sprocket hole
  |XXoX|                                    |XoXX|
  |XX X|                                    |X XX|  'X' = mag. track area
  |XXoX|                                    |XoXX|
  |XX X|                                    |X XX|  (registration hole not
  |XXoX|                                    |XoXX|   shown in this diagram)
  |XX X|                                    |X XX|
  |XXoX|____________________________________|XoXX|
  |XX X|                                    |X XX|
  
  |<---------------- 69.95mm ------------------->|
  |<---------------- 2.754in ------------------->|



 

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