Camera Characteristics - Sony BVP-E10 Series Product Information Manual

10
10-3.

Camera characteristics

Chapter 10 Glossary - Terms and Definitions
170
BVP-E10 Series Product Information Manual
Most of the camera characteristics cannot be properly
represented by numbers on a specification sheet.
Good values do not always equal good picture quality.
Judging by human eyes is one of the most important
processes to evaluate a camera. The following are a
few technical terms to be familiar with:
Modulation depth
Modulation depth is one aspect of a camera's
fundamental performance, and relates to its ability to
respond to the fine details in a scene. To evaluate this,
the camera shoots a Multiburst or frequency sweep
chart containing closely spaced black and white
vertical lines. This explores the frequency
characteristics of the camera between 0.5 MHz and 5
MHz or higher, and the camera output measured using
a waveform monitor. Gamma, Knee and matrix should
be switched off for this test. When image enhancement
(detail) is switched off, all cameras will show a
response that falls off with increasing frequency, but
that fall should ideally be small. Depth of Modulation is
usually expressed as the output at %MHz in relation to
at 0.5 MHz, in percentage terms. With detail switched
on, the same technique can be used to set the detail
correction to flatten the frequency response. If
excessive detail is used, the picture will look unnatural,
and noise will be worsened.
Power consumption and heating
Most of the power consumed by the camera turns to
heat, which can lead to poor performance, reduced
stability and unreliability. Also, when the camera is
used hand held, or shoulder mounted, excessively
high temperatures of the camera can be very
uncomfortable for the operators. Using a cooling fan to
reduce the temperature is not a good solution,
because it can lead to unwanted audible noise. So, low
power consumption is an essential factor.
Reliability
Reliability is one of the most important factors when we
evaluate a camera. Unlike other broadcasting
equipment, cameras are often used outside under
severe circumstances such as live broadcasting of
skiing events below the freezing point or of baseball in
mid-summer. For coverage of all live events, where
there is no opportunity to repeat a shot, reliability
always has first priority and a camera malfunction is
not acceptable.
Resolution
When talking about camera resolution, this usually
means horizontal resolution. Somewhat similar to
Depth of Modulation, this refers to the limiting
resolution of the camera - the smallest detail which can
be resolved. Again it is measured by viewing a
Multiburst or video sweep chart, but for convenience
this should be calibrated in TV lines (TVL). For
historical reasons, this measurement is rather
confusingly expressed as "TV lines per picture height"
- how many line pairs could be fitted into the height of
the picture. Great care should be taken when
comparing the performance of 16:9 and 4:3 cameras.
Even if the cameras have the same subjective
appearance, the 16:9 camera will always have a lower
numerical resolution. In the past, tube cameras had
resolution that was similar to that of the TV system as a
whole. However today, modern cameras can have
resolution of 900 TVL or more. Since the TV system
bandwidth is closely defined (limited to around 500
TVL in the case of the serial digital interface), camera
resolution is less important, and the performance in the
actual video bandwidth - Depth of Modulation - is
much more important.
S/N (signal-to-noise ratio, or SNR), Sensitivity and
dynamic range
In a good camera, the noise level will be low, and
difficult to see in a normal picture, but is most evident
when the camera is capped, producing only a black
output. The black level is amplified by gamma and
camera gain greatly affects the S/N, which can vary
between different manufacturers and even - different
models from the same manufacturer.. S/N is also
changed by different DTL settings. To provide a
standard measurement, it is usually measured when
IRIS is closed, gamma is off, DTL is off, Chroma is off,
and the pedestal level is set at 5%, and with the
measuring instrument set to measure in a specified
bandwidth. It can also be instructive to measure the
camera under normal operating conditions, with all
corrections switched on. However, since these
operating settings will vary a lot between different
users, they are not included in specification sheets.
There is a close relationship between S/N,
sensitivity, and dynamic range. When we raise the
sensitivity, the S/N and dynamic range will decrease.
So a key part of camera design is to choose the
optimum balance between these conflicting factors.
Although the measured value of the S/N is important, it
seems that the subjective visual assessment of the
picture under actual operating conditions is vital to
understanding the real performance of a camera
system.
Weight and balance
Clearly, less weight is better for shoulder-operated or
hand held equipment. However, for operating comfort,
the balance of the camera and lens combination is of
even greater importance.