sundance 2006 - Zoael

ment that the contrast detail reproduction
of the HD lens-camera system
in the 35-70 Lp/mm region was especially
important to the subjective
“look” of the imagery. This proved
especially true on facial close-ups
when the lens aperture was close to
wide open (a setting popular with
those DPs seeking a shallow depth of
field). These findings provided a first
clue. Bearing in mind that the norm of
imagery for film DPs is, naturally, the
film print projected onto a large
screen, it was felt that another clue
might emerge from a consideration of
the film lens-camera resolution and
the modifications to this that result
from traditional film processing steps.
Canon was challenged to seek a
technical solution to the dilemma of
preserving as high a resolution as
possible at all lens settings of focal
length and aperture, but at the same
time to also introduce a modification
of the level of contrast over the 30-70
Lp/mm spatial frequency region that
might better emulate the behavior of
the film camera and film processing
system. But this, only when the lens
is operating at close to a wide-open
aperture on close-ups.
Powerful computer simulation tools
are available to today’s optical designers.
These tools facilitate all forms of
exploration of the use of different optical
materials, lens element designs,
and optical coatings. The simulations
can show the impact of all of these
design variables on lens-image performance
and on optical aberrations.
Even more important, the collaboration
between the HD camera manufacturers
and the optical manufacturers
has also produced very accurate computer
simulations of HD camera characteristics.
On this particular project
the design engineers manipulated
optical design characteristics for the
lens to search for an overall lens-camera
system image sharpness and color
reproduction that would be more
appealing to the film DPs.
On the issue of picture sharpness,
the design optimization remained
empirical in the sense that the computer
was programmed to progressively
alter appropriate designs that affected
the referred-to 30-70 Lp/mm midband
contrast levels of the lens while
the results were subjectively judged by
the DPs on projections of the simulated
images onto a large screen. The
goal was to effect an adjustment to the
degree of sharpness that synthesized a
“look” on human facial close-ups, producing
an approximation to those seen
on 35mm film projected on a large
screen. For the quest on color reproduction,
simulations of carefully controlled
alterations to the light transmission
characteristics of the lens
were also programmed and subjectively
reviewed on the large screen.
Based upon the consensus that
emerged from this work, a prototype
91
model of the new 5.5-44mm T2.1
zoom lens was ultimately built to the
agreed specifications. Manufacturing
tolerances in HD lenses are so tight
that the design simulation could be
accurately reproduced in the actual
optical elements’ manufacture. The
DPs then tested the prototype lens
on the 24p HD camera. Their many
comments included a general agreement
that an important step had
been taken in realizing an HD cine
lens-camera combination that produced
perceived picture sharpness
on human faces and color reproduction
that was pleasing to film DPs.
THE ACV-235 ANAMORPHIC CONVERTER
An important extension of the collaborative
work between Canon and
the DPs was the development of an
optical solution to their additional
request for widescreen CinemaScope
capabilities with 24p digital HD cine
systems. This project produced the
world’s first optical anamorphic converter
for 2/3-inch 24p cine systems.
The converter mounts between the
2/3-inch cine lens and any of the available
2/3-inch digital cameras. It is a
high performance and innovative
design that optically compresses the
output object image from the lens by a
factor of 1.32 in the horizontal direction
and thus ensures that the input
2.35:1 scene content fully occupies the
total 1.78:1 image plane of the camera’s
HD imagers (1.78 x 1.32 = 2.35).
The HD video is subsequently digitally
uncompressed in postproduction prior
to the actual film-out. This maximizes
the overall spatial resolution of the
captured HD image and obviates the
need to “crop” a widescreen image
from a normal 16:9 image capture in
postproduction. This, in turn, produces
a higher overall picture sharpness
on a film-out. The results, as seen
on a final large film projection system,
have been lauded by those who have
used this device, known as the ACV-
235 Anamorphic Converter.
CONCLUSION
So which should be used for digital
cinematography? Cine lenses, such as
Canon’s line of HD-EC primes and
zooms? Or portable HD lenses originally
designed for the ENG/EFP needs of
the television/video world? The answer
is: Whatever the digital filmmaker is
comfortable with. What have long been
parallel universes of emulsion-based
and electronic production are now
intersecting in the age of digital 24p,
and this trend may continue. For now,
however, two separate shooting styles
with long traditions are being accommodated
in a range of HD lenses that
fill the needs of every digital filmmaker.
Larry Thorpe is National
Marketing Executive and Gordon
Tubbs is Assistant Director, respectively,
of the Canon Broadcast &
Communications Division.