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Panasonic's VariCam: An industry workhorse
(Broadcast Engineering)Pro shooters have come to swear by it and not at
it a remarkable achievement in itself for a complex
electro-mechanical device. The Panasonic VariCam has earned its
reputation as an industry workhorse, performing with great
reliability while producing superb images under extreme
conditions.
The camera's natural fall-off of image contrast and color
saturation in the shadows has always been a notable advantage; its
DVCPROHD 100Mb file size also proves more practical and manageable
than other HD codecs on desktop workstations and servers. In many
ways, however, the camera is still a work in progress. Indeed,
low-light performance and noise issues have been addressed in the
latest VariCam model the AJ-HDC27H.
Basic setup
As is the case when working in the HD arena, the camera's setup
requires a sufficiently large monitor (15in or more) to properly
assess focus, detail level and colorimetry. My pet peeve with most
HD cameras, including the VariCam for that matter, is the tiny
viewfinder that fails to provide sufficient reassurance of focus
during normal camera operation. It's only logical that the
shooter/engineer uses a large enough monitor to see HD's higher
resolution and what the heck he or she is recording.
The VariCam akin to most broadcast cameras features a dual
filter wheel that should be positioned to reflect ambient lighting
conditions. Tungsten (3200 K), daylight (6300 K) and
mixed illumination (4300 K) settings are provided along with
the usual exposure control filters: clear, ND, 1/16 ND and
1/64 ND. In general, shooters should use the strongest ND possible
in order to achieve the widest aperture setting. This will help
reduce the excessive depth of field condition as well as
diffraction anomalies that lead to a significant loss of
contrast.
The unit's claim to fame in many ways is its 720p imager, which
allows variable frame rate flashing. This is a capability not found
in cameras such as the Sony HDW-F900, which features interlace-type
imagers. Variable frame rates from 4fps to 60fps in 1fps increments
are selectable now in the camera via a USER button, giving the
shooter additional flexibility in higher-end commercial and
documentary production.
During my nearly 20 years at the National Geographic, I recall
very few scenes (other than sync interviews) shot at
normal 24fps speed. Shooting out of moving cars or
capturing wildlife with long lenses usually demanded higher than
normal frame rates just so subjects appeared normally paced on
screen. In other words, the (film) camera's variable frame rate
capability was not used solely, or even mostly, for slow-motion
effects. The savvy shooter uses the camera's multiple frame-rate
capability the same way subtly, almost imperceptibly.
Setting exposure
In simple terms, correct exposure reproduces white as white,
gray as gray and black as black. The shooter targeting a white or
gray card typically adjusts the iris while referencing the camera's
two sets of zebras. I usually set pattern 1 to 70 percent and
pattern 2 to 98 percent. If you're confused by the jumble of
diagonal lines covering the frame, you can disable the lower set;
the upper pattern provides a reference to guard against
clipping.
Gamma drama
The VariCam 27H features three gamma curves, two curves for film
output and film-like video output, and the traditional video gamma.
In the menus, one can select FILM REC mode, which at 9.5 stops of
latitude is optimized for output to film scanners. The VIDEO REC
gamma also incorporates the extended dynamic range of film while
ultimately anticipating output to the video sphere. While some
users will appreciate the VariCam's multiple gamma settings, most
broadcasters will prefer the standard video gamma for live
programs, including sports.
Independent filmmakers and shooters of narrative fare generally
will opt for the gentle toe and heel characteristic of cine-look.
The cine-look gamma produces more gradations of gray in the shadow
areas, which can be desirable as it often adds life to the darkest
areas of the frame. On the other hand, the same shadows, if
severely underlit, may appear washed out or noisy when lifted in
this fashion. For this reason, an on-camera fill or frontal wash
should always be considered, especially when shooting close-ups of
talent, because overly dark facial shadows may exhibit substantial
noise and unusual hue shifts.
The same drill applies for black stretch. If black stretch is
applied too aggressively, random noise may bloom in the shadows and
wreak havoc throughout a production. Such defects may appear
trivial on a set's production monitor, but single-pixel artifacts
often are amplified and can become serious troublemakers during
subsequent compression to DVD or satellite.
Grappling with noise
The AJ-HDC27H addresses the noise issue head-on (literally) as
the new imager and block lowers the noise floor considerably. The
model achieves this in part through improved heat dissipation
through the front of the camera. It feels warmer to the touch at
the front of the housing, which is reassuring. It means the
camera's redesigned signal amplifier and beefier heat sinks are
doing their job.
Panasonic also reduced the noise previously apparent in the blue
channel when shooting in low light. This was one of my criticisms
of the 27F; the camera lacked flexibility under such conditions. In
the updated model, an alternative low-light algorithm is provided
for shooting weakly illuminated scenes. Under most routine
conditions, shooters will still want to stay with the VariCam's
normal compression scheme. For the occasional challenging setup at
low or no light levels, however, the alternative setting provides
superior results.
There's another dimension to this noise discussion as well. The
camera now incorporates a more precise 12-bit DSP (as opposed to
the 10-bit version in the previous model), so sampling is more
accurate, and a greater amount of highlight detail can be retained.
This means that hot areas of the frame such as an exterior window
are less likely to appear blown out as the oversampled detail is
squeezed into DVCPROHD's 8-bit gamut. The additional detail helps
reduce the risk of noise appearing in these areas.
More to gain
The camera allows a range of gain settings to boost (or reduce)
the imager's analog signal. Levels of gain up to +30dB or higher
(+36dB with super gain enabled) are possible albeit with
dramatically increased noise that may negate any benefit derived in
the first place from improvement in gray scale. Many shooters and
engineers looking ahead to compression for DVD, satellite
transmission or video on demand may want to use a negative gain of
-3dB or even -6dB to suppress this shadow noise. But be careful:
Blacks can become impenetrable at very low gain levels, so caution
must be exercised.
A better and simpler approach in my experience is the use of a
camera filter to lift dark areas of the frame. The Schneider
Digicon or Tiffen Ultra Contrast filter can help transfer surplus
highlight values into deficient shadow areas. In urban night
scenes, the ultra contrast-type filter is one of the best things
you can do to improve the look of your VariCam images. This applies
as well to ENG-type footage frequently shot under such
conditions.
Conclusion
Many noise-related improvements in the AJ-HDC27H have their
roots in Restrictions On Hazardous Substances (ROHS), a recently
adopted mandate that has impelled manufacturers to redesign
products in accordance with environmental concerns. Fortunately,
Panasonic used the opportunity to address key performance issues,
most notably the lowering of the noise floor in the VariCam
imager.
Barry Braverman is a veteran cinematographer with more than
20 years experience in feature films, documentaries and music
videos. He is currently serving as a digital media expert and
consultant to major studios. His latest book, Video
Shooter, is available from CMP Books atwww.cmpbooks.com.
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