high-speed cameras
to allow the analysis of a high-speed
event? At the low end of the market, highspeed
cameras can capture images
at around 1000fps at 1-megapixel
resolution. At the high end they can run
at frame rates in excess of 20,000fps at
1-megapixel resolution.
Most high-speed cameras can run at
increasingly higher frame rates as the
pixel resolution is reduced. However, the
increased frame rate is never completely
proportional to a reduction in resolution
and typically comes with restrictions
regarding the specific numbers of
horizontal and/or vertical pixels that can
be selected for the reduced resolution.
There is a very wide range of
performance levels and a wide range of
costs for high-speed cameras. It is
important to make certain that there is
a close correlation between the application
requirement and the performance of
the camera so that additional money is
not spent unnecessarily for frame rate
performance that is not required. At
the same time, it is important to invest
enough money to ensure that the camera
provides adequate frame rate performance
for the application.
LIGHT SENSITIVITY
In many applications light sensitivity is
the most critical consideration when it
comes to purchasing a high-speed camera
because it affects so many things. Light
sensitivity impacts the ability to use a
short exposure time to effectively
eliminate motion blur when capturing a
very high-speed event. Light sensitivity
impacts the overall quality of the video
because without sufficient light
sensitivity the images will be dark and
hard to analyze.
Light sensitivity impacts the ability to
focus, especially when using telescope or
microscope lenses. Such lenses typically
have high F-numbers and if the aperture
must be set completely open to get enough
light onto the camera sensor, then the
depth of field will be extremely narrow. A
narrow depth of field makes it difficult
or impossible to focus on anything but a
very thin plane within the camera’s field
of view.
There is a huge variation in light
sensitivity among the high-speed cameras
bending of the light creates a spatial
variation in the intensity of light, and this
can be visualized with the use of a highspeed
AEROSPACETESTINGINTERNATIONAL.COM // SHOWCASE 2020 85
camera.
Schlieren Imaging is often used in
conjunction with wind tunnel testing to
design aircraft with improved efficiency
and reduced turbulence. For example, it
can be used in a wind tunnel to visualize
and measure hypersonic boundary-layer
instabilities on aircraft. When
implemented on a larger scale, Schlieren
Imaging can be used to visualize shock
wave propagation of explosive effects
on aircraft as well as the shock wave
produced from a supersonic aircraft.
When there is a change in the density of
the air caused by the different refractive
index of a shock wave, it is easily visible in
the high-speed image.
There are a number of factors that are
important to consider when purchasing a
high-speed camera to accomplish these
imaging techniques, including frame rate,
light sensitivity, minimum exposure time,
and pixel resolution.
FRAME RATE
The first and most obvious consideration
is how many images per second are
required to capture sufficient video detail
Particle Image Velocimetry (PIV) helps
engineers understand the fundamental
movement of liquids, gases and plasmas,
collectively known as fluids. PIV analyzes
high-speed video to identify and measure
the movements of tracer particles that
have been added to the fluid being tested.
The particle movements are examined to
provide automatic calculations and
visualization of the fluid flow. For
effective visualization, these movements
can be displayed as a series of velocity
vectors representing the movement of the
flow over time.
PIV is used in aerospace testing to
measure flow turbulence and vortex
structures. For example, PIV is used to
study the aerodynamics of an aircraft
wing as air travels around the wing inside
a wind tunnel. PIV is also used to evaluate
engine designs through the measurement
of combustion processes to gain insight
into combustion flow fields.
Schlieren imaging is used as a means of
visualizing changes in pressure and
temperature, as well as shock waves,
moving through a transparent fluid such
as air. This imaging technique relies on
differences in refractive index caused by
density gradients in the fluid to bend light
that is passing through the fluid. The
1 // The FASTCAM
SA-Z was used to record
a fuselage drop test using
Digital Image Correlation
during a recent study
conducted Wichita
State University
2 // The FASTCAM Nova is
a compact and versatile
high-performance highspeed
camera system
“the higher the resolution of
the camera, the lower the
maximum frame rate will be”
PHOTRON’S NEW
FASTCAM NOVA
Photron has recently
announced their FASTCAM
NOVA camera. The FASTCAM
NOVA brings together CMOS
image sensor technology and
extensive high-speed digital
imaging expertise to provide
a camera with great flexibility
for use in a wide variety of
applications. Available in three
different models, the FASTCAM
NOVA offers 12-bit image
recording rates up to 12,800fp)
at megapixel image resolution,
shutter speeds down to
0.2μs, and recording rates to
1,000,000fps at reduced image
resolutions. The camera is
rugged, compact, lightweight
and provides the best light
sensitivity in the market.
2
/AEROSPACETESTINGINTERNATIONAL.COM