Design Improvement for film projectors

projection
Design
Improvements
for Motion
Picture Film
Projectors
by Christopher L. DuMont, Andrew F. Kurtz,
Barry D. Silverstein, and David H. Kirkpatrick
DuMont
Kurtz
Silverstein
Kirkpatrick
page 6
With all the recent hype about digital
cinema, it is all too easy to forget that
there are still only a handful of high
quality D-Cinema systems in operation throughout the world, compared
with the hundreds of thousands of
conventional cinemas which are still
using and which will continue to use
35mm film for many years to come.
The 35mm film projector in use today
is little changed from its counterpart
of forty years ago, simply because the
basic mechanisms work well and give
little trouble. Unfortunately, this very
reliability has had the negative effect
that in recent years very little research
and development has been done on
ways in which the standard 35mm projector might be improved. This paper,
which resulted from work instigated by
Kodak Research Labs, describes how
the previous lack of research in this
area is being put right, and highlights
some fascinating new developments
that could prolong the useful life of
opto-mechanical film projection long
into the era where digital cinema
might otherwise have been expected to
take over.
This paper describes design
improvements developed for
motion picture film projectors
that are intended to improve
the quality of the overall
screen image. In particular,
new designs for the intermittent, or Geneva mechanism,
and for a “Universal” lamp
house are described. These
improved designs allow the
system light efficiency and
uniformity to be improved,
resulting in significant increases in screen luminance.
Motion picture film projectors
have been successfully used in
theatres for decades to project
high-quality images with broad
audience satisfaction. Indeed,
relative to qualitative parameters
such as image resolution, color
reproduction, contrast range, and
the elusive “film look”, motion
picture film has provided image
quality generally unmatched by
electronic projection systems. On
the other hand, the film experience has been degraded by a
multitude of factors, including the
film release print process, image
unsteadiness, film buckle or flutter,
poor illumination, dye fade and
wear, and physical artifacts such as
scratches and dirt. Aside from the
development and popularization of
very large screen film formats (such
as 70 mm) and the associated
projection equipment, the industry
has made very few design changes
to film projectors which actually improve the on screen image quality.
Indeed, the state-of-the-art motion
picture film projector1 has changed
very little from those produced
in the 1950s when robust color
films and xenon arc lamps were
introduced. Granted, projected
image quality has been significantly enhanced over the years by
progressive improvements in the
design and manufacturing of the
projection lenses. However, many
of the basic mechanisms within film
projectors, including the intermittent film drive, the shutter, and the
illumination system or lamp house,
are relatively unchanged since the
1930s. Thus, there continue to be
opportunities to make design improvements to the classic opto-mechanical motion picture film projector, which could, in turn, improve
the projected image quality.
It is well known that a significant
percentage of the commercial
theatres fail to meet SMPTE 196M
standard which specifies 35 mm
film projection at 16 (±2) fL
luminance at screen center, with
a nominal 20% fall off to the
corners. Indeed, it is commonplace for commercial theaters to
only provide 6-10 fL luminance at
screen center, with 30-50% fall-offs
to the corners. Although much of
this performance difference can
be attributed directly to cost cutting
by the exhibitors, deficiencies in
projector design relative to light
efficiency (and ease of use) also
contribute to this slippage. Design
improvements related to light delivery in a film projector can provide
both direct benefits to the screen
illumination,2 but also indirect
benefits related to alignment and
robustness, ease of use, and image
quality. As the light efficiency in
a traditional motion picture film
projector is largely determined
by the operation of the intermittent film drive and the design of
the lamp house, design changes
in these areas offer the greatest
potential for an economical, quality
improvement.
The Geneva Mechanism
Geneva mechanisms are widely
used in motion picture film projectors to intermittently advance the
film through a film gate having a
projection aperture. The film is
moved or advanced by a Geneva
mechanism until an image frame
is in alignment with the projection
aperture. The film is then held
stationary for a discrete period during which light is passed through
the aperture, film frame, projection
lens, and onto a screen. This intermittent frame-by-frame motion of
the film is enabled by the Geneva
mechanism shown in Fig. 1, which
consists of a continuously rotating
driver and an intermittently rotating
cinema technology - june 2002
projection
Fig. 1: Standard Geneva Mechanism and motion throgh index
star wheel. In a motion picture
projector the star wheel shares its
central shaft with a sprocket, the
teeth of which are engaged with
perforations in the film. Therefore,
when the driver moves the star
wheel, both the star wheel and the
film experience a resulting intermittent motion. Motion picture film is
typically projected at a rate of 24
fps, such that a new film frame is
positioned in the projection aperture every 1/24 second, or~42
ms. The standard projector Geneva
mechanism moves a film frame
into the projection aperture with an
indexing time of ~1/4 of the frame
period, or ~10.5 ms. As shown in
Fig. 2a, the star at first experiences
a slow acceleration, followed by a
rapid increase to a peak acceleration, and then a sudden reversal to
peak deceleration, after which acceleration gradually tapers off. As
a result, the star, sprocket, and film
are slow to get going, with minimal
displacement for the first ~15
degrees of driver rotation, and thus
only gradually reach peak velocity,
before slowing down during the
deceleration phase. The timing
relationships of the star movement
and shutter operation are shown in
Figs. 2b and 2c. During essentially
all of this indexing time, the shutter
blocks the light incident to the film
and prevents the appearance of
“travel ghost”. The projectable
Fig 2. : Timing diagram for a standard Geneva mechanism
cinema technology - june 2002
frame time, which would appear to
be 3/4 of the total frame period, is
further reduced to only 1/2 of the
total frame period, as the typical
projector employs a two-bladed
shutter to provide two blanking
periods per frame, thus boosting
the apparent frame rate to 48 fps,
and thereby reducing the flicker
perceived by the human eye. Furthermore, it is necessary for these
two shutter intervals to be equal in
duration in order to limit perceived
flicker. Therefore, because one
blanking period must be 1/4 of the
frame time in order to blank the
projected image as the film moves,
the other blanking period must be
of essentially the same duration.
The star wheel is the key element in
enabling the Geneva mechanism
to convert uniform rotary motion
to incremental rotary motion. Traditionally, the projector star wheel
has four radially extending straight
slots spaced equally around the
periphery of the star. Interposed
between these slots are concave
cam guide surfaces, which, like the
slots, are uniformly dimensioned
and arranged. A driver, comprising a restraining cam, a drive
arm, and a drive pin near the far
end of the drive arm, is employed
for indexing the star wheel. The
restraining cam has a side cam
surface, which is convex, and configured to interact with the concave
cam guide surfaces of the star
wheel. The close contact of this
convex cam surface to the concave
cam guide surfaces restrains the
star wheel from experiencing rotary
motion except during the periods
in which the star wheel is driven
by the drive pin. The star wheel is
thus restrained intermittently, and
in a manner such that the straight
slots sequentially receive the drive
pin. Thus, in the conventional
projector intermittent, each 360o
revolution of the driver produces
90o of rotation of the star wheel
and attached sprocket. Correspondingly, a standard two-bladed
shutter utilizes a pair of opposing
blades each providing beam blockage over 90o of its own rotation.
As can be seen, if the indexing
time of the Geneva mechanism
could be reduced, the shutter
blanking periods could, in turn,
be shortened, thereby increasing
the available screen light visible
within a frame. Most simply, the
indexing time might be reduced by
using a star wheel which has only
three straight slots. In that case,
engagement of the star wheel with
the driver pin occurs over only
60o of the 360o revolution of the
driver, thus providing an indexing
time of ~7 ms per frame to move
a film frame into the projecting
aperture. While a 3-slot star wheel
would thus decrease the indexing time (and thereby increase
the available projection time), the
acceleration forces applied to the
drive pin, slots, and the load (the
film and film perforations) are
greatly increased over those of a
4-slot Geneva, making the 3-slot
mechanism undesirable for use
in a projector. While the drive
pin can be shaped3 to modify the
acceleration profile and reduce the
forces on the drive pin, a 3-slot
Geneva mechanism would still be
prone to failure in a motion picture
projector application.
A variety of alternate designs
for the enhanced intermittent film
page 7
projection
drive mechanisms have been
control the steepness of the ascent
considered,4 the most successful of
to peak acceleration, the transition
which was the “Powers” move-
into mid index (the zero acceleration
ment. In the case of the “Powers”
point), and the acceleration profiles
movement, the star wheel employs
between these two extremes. At op-
four round pins, which engage
erating speeds, the drive pin enters
with a cam that has a single, large
a slot and rides along the concave,
diamond shaped cam driver. While
convex, and straight portions of
this intermittent reduces the index-
the first wall, and then exits the
ing time to ~1/5 of a rotation of the
slot by riding along the surfaces of
cam, by supplying prolonged peri-
the opposing wall in reverse order.
ods of uniform controlled peak ac-
Unlike the conventional projector
celeration to the star, a high sliding
Geneva mechanism, the drive pin
velocity may introduce unsteadiness
does not fit the star wheel slots,
and gradual pin wear. This likely
except in their deepest portions.
prevented the widespread adoption
As a result, the new Geneva can
of this mechanism.
experience some chatter at very low
5
speeds, as the drive pin separates
A New Geneva Mechanism
from the wall. However, at normal
A new Geneva mechanism for use
operating speeds, with the inertial
in motion picture film projection has
torque many times greater than the
been developed and demonstrated.
drag torque on the film, the drive
As opposed to the traditional
pin will remain in contact with the
mechanism, which uses a star wheel
appropriate wall of the slot, and the
with straight slots, the star wheel of
mechanism will function without los-
the new design employs slots with
ing control of the driven load.
curved surface profiles. It has been
To illustrate the design concept
shown that with the appropriate
more fully, a timing diagram (Fig.
shaping of the slot walls, the veloc-
4) shows the relationship of the
ity profile encountered by the star
acceleration and velocity of the
wheel can be modified to reduce
star wheel to the pin load and
the indexing time, while maintain-
the shutter operation during the
ing control over the acceleration
first half of a frame time. Basi-
and load forces experienced by the
cally, the curved slots are shaped
film and the drive mechanism itself.
to produce a prolonged period of
As shown in Fig. 3, the slot walls
high acceleration prior to mid index
of the star wheel have a concave
and a similar prolonged period of
portion adjacent to the mouth of
deceleration after mid index, after
the slot, followed by a slight convex
which the deceleration is rapidly
portion in the middle of the slot,
reduced to zero. Comparison of
and a straight portion innermost in
the timing diagram for the standard
the slot. The details of the design
Geneva mechanism (Fig. 2) and the
of the slot shape can be adjusted to
improved Geneva mechanism (Fig.
6
Fig 3. : The new Geneva mechanism
Fig 4. : Timing diagram for the new Geneva mechanism
4), shows that the acceleration and
slot profiles to provide different
velocity motion profiles are shorter
peak accelerations, pin loads, and
and more abrupt at the beginning
indexing times. A variety of designs
and end of index. While in the
have been modeled and tested,
conventional Geneva, the drive pin
including a device that has nearly
is engaged with the slot over 90o
an identical indexing time to that
of rotation, the drive pin of the new
of the conventional mechanism,
mechanism enters the shaped slot
but has reduced peak acceleration
later and leaves earlier, effectively
and peak pin loads (50% and 55%
engaging over a lesser angle. As
respectively), for reduced forces and
the star wheel undergoes a smooth
wear on the mechanism and on the
and continuous motion through mid
film. Alternately, an increased peak
index, the pin load (Fig. 4c) remains
acceleration and peak pin load can
under control, thus minimizing both
be traded off for reduced index-
the applied forces and the wear
ing times, which is, of course, the
experienced by both the mechanism
intended goal. One such design
and the load (the film). As the
utilized shaped slots that provided
design concept specifies deliber-
a dramatically reduced indexing
ate shaping of the slot walls, which
time (64% or 6.7 ms) with increased
have a relatively large surface
peak acceleration and pin load
area, wear on the mechanism is
(142% and 106% respectively) com-
minimized as compared to alternate
pared to the conventional Geneva.
approaches involving shaped or
Thus, this version of the “Quicker-
high load drive pins.
mittent” completes its indexing over
Within limits, the new Geneva
only 56o of rotation of the driving
mechanism, or “Quickermittent”,
cam, compared to 90o for the
is amenable to a wide range of
standard mechanism and
potential designs utilizing different
page 8
cinema technology - june 2002
projection
Fig 5. : The standard star wheel, the driving cam and the new star wheel
provides 36% more screen light
during a frame time. A third, less
aggressive design, which has also
been evaluated, provided reduced
indexing times (73% or 7.7 ms
or 66o rotation) and ~27% more
screen light, with peak acceleration
and peak pin loads comparable to
the conventional Geneva (100.6%
and 91% respectively). As shown
in the timing diagram of Fig. 4d,
each of the shutter blades will be
closed for less time than in the
conventional projector, and the
perceived screen luminance will
be proportionally increased during
each frame. Of course, the actual
light gain achieved on screen will
be reduced somewhat relative to
the design and tuning of the shutter
to minimize “travel ghost”, which is
the visual perception of the moving
film.
Thus far, “Quickermittent” Geneva
mechanisms have been successfully
prototyped and tested in Christie,
Simplex, and Century projectors,
using hardware appropriately
adapted for each system. Figure
5 illustrates the “Quickermittent”
star wheel, with its curved slots,
along with the standard star wheel
and cam. When it is designed to
work with the same cam driver, a
new star wheel is actually slightly
smaller than the standard star
wheel. In general, a “Quickermittent” can be retrofit into an existing
projector, using the modified
star wheel and a conventional
or slightly modified cam driver,
and with little or no change to the
remainder of the projection head.
Gate tension may be slightly
higher in a projector modified
with a “Quickermittent”, in order
to provide sufficient film drag to
page 10
maintain control over the film and
to prevent film or mechanism damage. Preliminary tests also have
indicated that the “Quickermittent”
tends to be somewhat noisier than
the conventional mechanism, but
the increased noise levels are likely
acceptable, and can be minimized
with proper adjustment and design.
Before widespread adoption by
the projector manufacturers and
exhibitors, extensive field trials
and design optimization are likely
required to validate and improve
the performance of the “Quickermittent”.
The Projector Lamp House
The successful development of
a lamp house useful for motion
picture film projection appears to
have been one of the first great
illumination design problems of the
industrial age. Many of the classical illumination optical designs,
from the Köhler system,7 to the fly’s
eye illuminator,8 and the elliptical
reflector were either conceived of,
or enhanced, in order to project
film images. Generally, the conventional lamp house used in motion picture film projectors consists
of a short arc xenon arc lamp inset
within a deep-dish elliptical mirror. Compared to the numerous
alternatives, many of which involve
combinations of reflectors and lens
elements, the basic lamp house,
with its single circularly symmetrical
elliptical reflector, is notable for its
simplicity and low cost. However,
as the typical lamp house overfills
the rectangular film aperture with a
large round beam of light, this system is quite inefficient. Moreover,
alignment of these lamp houses,
whether of the xenon arc to the
first focus of the ellipse, or of the
reflector and lamp to the projection
aperture and lens, has proven sufficiently difficult and time consuming in that the effort overwhelms
many theaters. Although, over the
years, various opportunities have
been available for improvement
in lamp house design, many of
the efforts to date were directed to
small adjustments in the design of
the elliptical reflectors and coatings, or to debates over whether
to utilize horizontally or vertically
installed xenon arc lamps.
The “Universal” Lamp House
A new lamp house has been
designed and prototyped, with the
objective of improving the light
efficiency and uniformity of the
light delivery to the screen, as well
as improving the robustness and
ease of alignment. In particular,
the new lamp house was designed
utilizing a fly’s eye optical illumination system working in combination with modern xenon arc lamp
modules. The fly’s eye optical
system, which uses lenslet arrays to
reshape and homogenize the light
beam, was originally developed
by Zeiss Ikon8 in the 1940s. This
design approach, which was later
adapted to work in combination
with the short arc xenon lamp,9
was considered difficult to use
because of alignment issues with
respect to its “waffle” lens. In
all likelihood, the widespread
adoption of a fly’s eye design in
cinematic projection was limited by
the cost and difficulty of manufacturing the required lenslet arrays.
However, in recent decades, light
homogenizing illumination systems
employing either a fly’s eye design
or kaleidoscope optics have been
extensively developed for the
photolithography industry. More
recently, such designs have been
successfully applied in the design
of electronic projection systems, using xenon, metal halide, and other
arc sources. Furthermore, when
such systems are properly designed
and implemented, the optical
alignment is actually less sensitive
to misalignment as compared to
the equipment used in conventional systems.
As shown in Fig. 6, the new
lamp house employs a series of
condensing lens elements and two
lenslet arrays in a classical fly’s
eye optical system between the
lamp and the film gate. The first
condensing lens after the lamp is
used to fill the first lenslet array
with a specular beam. The first
lenslet array, which is constructed
of spherical lenses with rectangular
apertures, breaks this beam into a
Fig 6. : Optical layout with the ‘Universal’ lamp house
cinema technology - june 2002
projection
series of beamlets that are coupled
to the corresponding lenslets of the
second array. The second lenslet
array, working in combination with
a relay lens, images the lenslets of
the first array onto the film gate in
overlapping fashion, thus providing a rectangular area of uniform
illumination. A field lens, located
near the film gate, is used to image the second lenslet array into
the entrance pupil of the projection lens. As compared to the
fly’s eye designs of prior years,8,9,
this system not only benefits from
modern manufacturing methods
for producing lenslet arrays, but
also utilizes modern light sources.
In particular, the prototype “Universal” lamp houses are designed
to accept either the CermaxTM EX1500-F and EX-2400-F short arc
xenon lamps, but also the MVDR
1.5 kW, MVDR 1.9 kW, and MVDR
3.0 kW Illumination Modules.
These lamp sources, which provide
brighter (low etendue) beams than
the traditional short arc xenon
bulb lamp and elliptical reflector
combination, are available from
Perkin-Elmer Inc. of Asuza, CA.
The CermaxTM lamps are integrated
lamp packages, in which the
electrodes, rare gases, and arc are
contained in an integrated package with datum features. As these
lamps operate with smaller arc
gaps compared to bulb lamps of
the same wattage, the arc plasma
is smaller, and the light source is
effectively brighter. By comparison, the MVDR modules combine
conventional short arc xenon bulb
lamps with compound reflectors,
to synthesize a brighter effective
source by capturing some light with
the secondary reflector. This light
is then recycled back through the
bulb and primary reflector. These
modular lamp sources, which are
for example used in the RoadieTM
series electronic projectors offered
by Christie Digital Inc., are relatively rugged and provide external
datum features for easy repeatable
installation. Within these modules,
conventional bulb xenon arc lamps
cinema technology - june 2002
are pre-aligned to the compound
reflectors, prior to installation in a
projector. Ushio Inc. also manufacturers a version of the modular
lamp source with compound reflector. In combination, with the use of
brightness enhanced xenon sources
and a fly’s eye system, which channels light through a rectangular
aperture, significantly brighter illumination is provided as compared
to the conventional system. For
example, a prototype lamp house,
constructed as described, demonstrated a ~35% light gain and 16
fL center screen luminance through
a ‘scope aperture when projected
on a 30 ft screen with a 114 ft
throw while using a 1500 W lamp.
Screen luminance data should
soon be available for the “Universal” lamp house equipped with 2.4
kW and 3.0 kW lamp sources.
The lamp house system of Fig. 6
also provides several secondary
advantages. In addition to the
added light efficiency, the screen
illumination has improved uniformity, with typically only a 10-15%
gradual roll off from center to corners. In practice, the efficiency and
uniformity improvements delivered
to the screen luminance by the
“Universal” lamp house are dependent on the choice of projection
lens used with a given system. The
process of light homogenization
also has the secondary advantage
of desensitizing the illumination to
flicker from arc and gas turbulence
within the lamp. Furthermore, the
fly’s eye type design desensitizes
the illumination to horizontal or
vertical misalignment of the lamps,
as shifts of ~1.0 mm will cause
minimal change in the illumination
uniformity. These tolerances easily
fall within the repeatability of alignment provided by the datum features of either the CermaxTM or the
modular lamp sources, thus providing simple, safe, and repeatable
lamp placement. Additionally, the
prototype system uses a CalflexTM
C infrared filter from Unaxis Optics
Inc., providing superior IR rejection
and a natural color temperature of
5500 K. Finally, the illumination
system can be optionally config-
ured10 to suppress the visibility of
scratches and dust on the film with
the addition of a holographic or
engineered diffuser located in the
gate upstream of the film.
A mechanically integrated version
of the lamphouse with improved
optics has been designed and prototyped. This system, as shown in
Figs. 7 and 8, had been designed
to be universally modular with
Christie, Simplex, and Century projectors with minimal modification
required for either the lamp house
or the projector heads. The Christie
and Simplex projectors need only
have some lamp baffling removed,
while the Century requires the
addition of a lens mount attached
to the main casting. This system
is compatible with both pedestal
and console style mounting, and
it accepts either the CermaxTM or
modular style lamp sources as
well. The opto-mechanics have
been designed to provide easy
accurate alignment of the lens
elements within the projector, and
easy integration and alignment of
the lamp houses with the projector
heads. To ensure robustness under
the high thermal loads, the various
lens elements are manufactured
from PyrexTM and are mounted with
pliant adhesives for low stress. The
thermal design within the “Universal” lamp house is engineered to
both minimize heat transfer among
components and modules and to
quickly remove heat from the various assemblies. Furthermore, the
“Universal” lamp house was designed for easy mechanical access
from both the sides and top, with
kinematic features to ensure alignment during servicing. Finally,
the “Universal” lamp house, with
approximate dimensions of 28.5
in. x 15.0 in. x 14.1 in. (LxWxH),
is significantly smaller than most
pedestal or console mounted lamp
houses used in projection systems
today.
Theater Application
The “Quickermittent” and “Universal” lamp house have been tested
in combination, and provided over
20 fL (7500 lumens) center screen
luminance on a ‘Scope
Fig 7. : Mechanical design of the ‘Universal’ lamp house
Fig 8. : Photograph of the assembled ‘Universal’ lamp house
page 11
projection
aperture 30 ft screen with a 1500
ules themselves. However, these
resolution. The standard two-
W lamp. Alternately, that is ~70%
modules can be re-lamped (usually
bladed shutter, which is typically
References
more light than provided by a
by the manufacturer or a specialty
located between the lamp source
1. “Motion-Picture Projection and
projector operating with a standard
vendor) and then re-used by the
and the film gate, causes the film
Theatre Presentation Manual”,
Chapter 6, Society of Motion
intermittent and lamp house
theater. With the modular lamp
to be pulse illuminated twice per
equipped with a 2 kW lamp (4500
sources, one lamp module can be
frame. The film buckles dur-
Picture and Television Engineers,
lumens). Projection with the “Flat”
exchanged for another within min-
ing the first illumination period,
New York, NY, 1969.
or 1.85 projection apertures shows
utes, without the need to re-align
relaxes some during the intervening
a less dramatic ~40% light gain, as
and refocus the bulb within the pro-
dark period, and then buckles (or
light is lost from clipping by the ap-
jector. Admittedly, the “Universal”
deforms) further during the second
erture plate (6500 lumens). Unlike
lamp house could be redesigned
illumination period. Film buckle
Vol. 92, pp. 1310-1313,
the many proposals for improving
to accept light from a conven-
can potentially be reduced through
Dec. 1983.
screen luminance by altering the
tional bulb lamp and lamp house,
either passive or active means,
basic 35 mm film format, these
however, the advantages relative to
by incorporating the appropriate
light gains can be achieved with
performance, size and, ease of use
design changes to the projector.
U.S. Patent # 1,198,683,
minimally disruptive upgrades to the
would be lessened. The ultimate
However, these design changes,
Sept. 1916.
existing projection equipment. The
question relative to adoption of the
which need further development,
light efficiency gains provided by the
“Universal” lamp house, with its
are more invasive to the design of
new intermittent and lamp house
modern xenon lamp sources, could
the projector head than either the
designs could simply be used to
be whether the advantages relative
“Quickermittent” or the “Universal”
provide a better screen image. Al-
to efficiency, ease of use and align-
lamp house. If, however, such
ternately, this efficiency can be used
ment, and performance outweigh
changes were adopted and the film
to light an existing screen with a
the additional lamp costs for the
buckle accordingly reduced, the
lower power lamp than used today.
cash strapped exhibition industry.
projected image quality would be
This combination has the additional
perceptually improved through the
2. J. Kelly and G. Berggren, “Screen
Illumination of 35-mm Film
Projection”, SMPTE Journal,
3. A. F. Victor, “Mechanical
Movement”,
4. A. Hayek, “Design Factors in
35 mm Intermittent Mechanisms”,
J. SMPTE, Vol. 49, No. 5,
pp. 405-414, Nov. 1947.
5. N. Power, “Intermittent Driving
Mechanism for Motion Picture
Machines”,
U.S. Patent # 1,129,121,
Feb. 23, 1915.
benefit of reducing the thermal load
Other Opportunities
present projection lenses provided
through the film, thereby reducing
Although new possibilities have
by ISCO or Schneider, or through
film buckle and the resulting shifts
emerged from the development
any new and improved projection
through focus, and thus improv-
efforts directed to the “Quickermit-
lenses which could be developed.
ing the image quality. Likewise,
tent” and the “Universal” lamp
the light efficiency gain can also
house, there are other significant
be traded away for a reduction
opportunities to improve the
Acknowledgements
in scratch and dust visibility in the
projected image quality provided
The authors would like to thank
projected image.10
by motion picture film projectors.
Eastman Kodak Company and the
Although both the “Quickermittent”
Compared to other effects which
Enhancing the Theatrical Experience
and the “Universal” lamp house
degrade the projected image qual-
(ETE) project team for supporting
have been successfully demon-
ity, such as scratches, dirt, and film
these and other development efforts
strated and tested, these designs
jump and weave, film buckle is the
directed towards improving motion
would benefit from field testing and
least obvious, but perhaps most sig-
picture film projection. Additionally,
optimization prior to widespread
nificant, contributor to quality loss.
Darryl Jones provided invaluable
adoption by the industry. Ad-
Borberg11 describes both the basic
assistance and advice in working
vantageously, both designs lend
phenomenon of film buckle, as well
with motion picture film projection
themselves to being retrofit into
as one solution involving modulated
equipment, while Franklin Ehrne
existing equipment or into current
air blasts to mitigate the effect.
provided considerable mechanical
projector designs with minimal
While much of the light incident
engineering and design support to
changes required to that equipment.
on the film is transmitted through
the project team. Consideration is
Illumination System and Method”,
Furthermore, the component and
it, and subsequently imaged to the
also due Gary Nothhard, for his
U.S. Patent # 5,754,278,
assembly costs for these designs
screen by the projection lens, a por-
continuing support in testing and
should be generally comparable
tion of this light is absorbed, either
characterizing the new lamp house.
to the existing equipment it would
by the dyes in the case of color film,
Finally, thanks are due Glenn
for Reducing Film Buckle”,
or by the silver grains in the case of
Berggren for providing many useful
J. SMPTE, Vol. 59,
black & white film. The absorbed
insights relative to the performance
pp. 94-100, Aug. 1952.
lamp sources cost more (as much as
light heats the film, which being
levels and developmental history of
2-3x more) than today’s xenon bulb
an elastic material, deforms out
the projection equipment used in
This article was originally published
lamps of identical power. While the
of plane. This thermally induced
the motion picture industry.
in the November 2001 issue of
CermaxTM lamps are simply more
deformation can shift the image
the SMPTE Journal, and the BKSTS
costly, the added cost introduced
outside of the designed depth of
thanks the SMPTE for its permission
by the modular lamp sources is
focus of the projection lens, thereby
to re-use the material.
mainly due to the cost of the mod-
degrading the on screen image
replace. Certainly, either the CermaxTM or the modular compound
page 12
6. D. H. Kirkpatrick and A. F. Kurtz,
“Geneva Mechanism and Motion
Picture Projector Using Same”,
U.S. Patent # 6,183,087,
Feb. 6, 2001.
7. A. Köhler, “Lighting System for
Cinematographs”,
U.S. Patent #1,143,287,
June 15, 1915.
8. K. Räntsch, “Illumination System,
Particularly for Projection
Systems”,
U.S. Patent # 2,326,970,
Aug. 17, 1943.
9. H. Ulffers, “Xenon High-Pressure
Lamps in Motion Picture
Theaters”, J. SMPTE, Vol. 67,
pp. 389-391, June 1958.
10.A. F. Kurtz, “Image Transfer
May 19, 1998.
11.W. Borberg, “Modulating Air Blast
cinema technology - june 2002
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