What’s the lens got to do with it? In HD shooting, plenty. The lens is
the arbiter between the live three-dimensional scene and the careful
two-dimensional optical extraction from that scene. What the camera
ultimately represents, digitally, is determined by the creative dynamic
between the person controlling the lens (the DP) and the program’s
director, lighting director, set designer, and of course, the talent.
For drama work, a DP, working with the director and lighting director,
can use a Canon HJ11ex4.7B lens (above) to capture a low-lit dramatic
mood while defocusing background detail. On a shoot for a reality show,
a Canon HJ22ex7.6B portable lens lets a DP follow an actor moving from
extreme close-up to a distant point in the scene-across a thoroughfare,
for example-while keeping everything else in the shot in sharp focus.

You can compensate for the loss of the third dimension, or depth, in a
live scene by artfully exploiting depth of field (a strictly optical
phenomenon) and perspective (the optical manipulation of foreground and
background that is also a useful optical occurrence). The Canon HD cine
lens HJ8x5.5 (above) has a maximum relative aperture of T-2.1. When
used with a contemporary 24p digital HD camcorder (having a sensitivity
specification of f-10 at 2000 Lux scene illumination) this can-under a
scene illumination of a mere 50 Lux, and at a focal length of 20mm,
with aperture set wide open-produce a depth of field of 24 inches. This
helps direct your viewer’s attention to different actors in a verbal
exchange when you pull focus between one actor and then the other. And
when you’re shooting in digital, you can see how this looks in real
time and make creative adjustments on the fly.

Some extreme wide-angle lenses let lens operators come close to
emulating the extraordinarily wide field of view of the human eye. The
zoom control (again a strictly optical tool) gives you real-time
control over that field of view, and can be used to powerfully enhance
the visual impact of a given scene. A wide-angle lens with a 4.7mm
minimum focal length and an 11:1 zoom range can capture an incredible
90-degree horizontal angle of view-for example, a stadium 1,000 feet
long from a distance of 500 feet. A long zoom portable HD lens, on the
other hand, with a 40:1 focal range, can image a rare bird full screen
from hundreds of feet away. Cinematographers, on the other hand, often
like working with a tightly controlled limited range of focal lengths,
and newer HD cine lenses offer zoom ranges tailored to such fine
control. Canon’s new HJ8x5.5B KLL-SC, having an 8:1 zoom range combined
with a very wide-angle 5.5mm, gives you an 82-degree horizontal field
of view.

Because HD video is far richer in picture sharpness than the present SD
NTSC television system, the added definition can add razor sharpness to
a close-up shot. It can also sustain a very wide-angle shot that, by
its very nature, is conveying to the camera a vastly greater amount of
scene detail than the close-up shot. Film DPs understand that lens
resolution is a complex science-it comes from years of trial and error
on set. Real-time monitoring while shooting HD greatly empowers the
DP’s control over lens-camera picture sharpness for different scene
content.

How a lens maintains contrast is critical. A lens must never
contaminate black reproduction-and high-performance lens designs go to
enormous lengths to minimize such things as flare, veiling glare and
reflections that can detract from a pure black reproduction. At the
other extremity, where strong light sources in a scene and creative
over-exposure, like sunlight through trees, might be important, the
lens should minimize artifacts and unwanted reflections. You can only
test the overall contrast performance of any given HD lens when it is
attached to an HD camera. A test chart will quickly reveal the purity
of the black reproduction and the accuracy of the grayscale
reproduction over your nominal exposure range. Shooting into strong
light sources, but moving the camera to position that source at the
peripheries of the image, will show you how your lens is handling
highlights and expose any optical anomalies.

The difference between an SDTV and an HDTV lens is huge. The HD lens
needs to resolve 2.7 times more than the best SD lens-a significant
extension in resolving power considering that both use the same small
2/3-inch image format. Over the past decade, astounding advances have
been made that have led to this higher resolution, as well as the
management of that resolution, from the center of the image to the
corners, and the way it handles when a user controls the zoom, iris and
focus.

One optical phenomenon common to all lenses-known as relative light
distribution-occurs when the light transmitted through the lens falls
off from the center out to the extremities of the image plane,
impairing the contrast performance of the lens from its center to its
corners. In turn, it adversely affects how sharp an image will appear
across the screen. Canon took special steps, particularly in our FJs
prime lens series (left), to achieve an especially even relative light
distribution in its cine-style lenses.

Larry Thorpe
National Marketing Executive
Broadcast & Communications Division
Canon U.S.A.

For more than 35 years Larry has been involved in video imaging.
Fourteen of those years were spent in studio-camera development at RCA
Broadcast and 20 years in HDTV market development at Sony Broadcast.
Today Larry has moved out in front of the camera to market lenses for
Canon. His fascination with video imaging, and HD imaging in
particular, has resulted in many technical papers on the subject,
published during the past several decades.

Never make the mistake of thinking that a lens is a mere accessory to
the camera-especially in HD imaging. The HD lens has the primary role
in shaping the image and giving it critical performance attributes
that, in turn, will determine the ultimate digital performance of your
camera.