American Cinematographer - April 2007 - 70

Rear
Playback
equipment
onstage. In the
background is

Projection Takes

a

Step Forward

the D-5 deck,
the LUTher box
and monitor. In
the

mid-ground

are

waveform

monitors, and in
the

foreground,
a

trackball

control

panel.

ing ANSI contrast ratio of 500:1,
meaning the actual brightness range
of a checkerboard image on screen,
including the complicated internal
light path combining three DLP
images and the projection lens.
So with care, we can put an

image
close

the screen that will look
reality on the final print or
display.
(Incidentally,
our
tests
on

to

video

showed that it

not

necessary to

and the playback
deck
the projector gets its frame
rate from the deck
as
long as both
were set to 24 fps. When the play¬
back speed was even slightly off,
color phasing was very apparent
sync

the

was

camera

-

-

across

the

screen.

For the

future,

syncing the deck and the camera
might be good insurance.)
Of course, the rear-projection
screen must

be uniform (free from

blotchiness). Then there is a delicate
balancing act between the transmis¬
sion

(brightness) of the screen and
degree to which it diffuses the
image. A very bright, more trans¬

the

missive

screen

will show the "hot

spot" typical of rear projection. The
hot spot is actually the diffuse image
70

April 2007

of the

bright projector lens seen
through the screen. The more distant
the screen is from the projector, the
smaller the hot spot, and, usually,
the less center to edge illumination
falloff. No technique exists to elimi¬
nate the hot spot in high-transmis¬
sion screens without harming the
quality of the projected image.
The product of many decades
of experience in translucent-screen
fabrication, Stewart Filmscreens
Aeroview screen material is

an

excel¬

lent choice for this

application. A
12'-wide projected white light was
remarkably uniform with the pro¬
jector just 20' behind the Aeroview
screen. We ran the projector 50'
from the

screen

for the actual shoot.

The

a projected image of this pho¬
tographed chart to match the real
thing on the stage, we would be a
long way to achieving the goal.
As the combined image (p. 72,
top photo) shows, with a calculated
LUT and successive adjustments,
first by eye and then with a Nikon
D2X digital still camera, it is possible
to get very close. The results dis¬
played on Lindenlaub's Kodak
Look Management System-calibrat¬
ed monitor closely matched the final

result

on

film.

In the setup

shown, the pro¬
jected image is the lower one; the
same chart array is held on C-stands
in the foreground and lit with tung¬
sten fixtures filtered towards daylight

slight left-to-right color cast is
an artifact of the DLP
projector.
In practice, the chart array
(p.72, bottom photo), shown in
front of its rear-projected image,
includes a good slice of the values
normally encountered in day-exteri¬
or
photography. A spotmeter set at

balance with Full CTB. With finer

ASA 200 measured the Kodak white

otherwise dark stage.

card

at

£22.8 and the black-velvet

patch at f2.81/3 - nearly 8 stops of
brightness range. If we could adjust

adjustment of the LUT, it might be
possible to get the match even closer.
The 4:2:2 bandwidth limits of D-5

tape may be a
at Vso

factor. Exposure is f5.6

second; the chart is too close to

the lens for

a split focus to carry.
This result was achieved on

an

Because the
point is to have a car with actors in it
in the foreground, the classic chal¬
lenge remains to light the fore-
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