high-speed cameras
that are out in the market. Light
sensitivity is typically presented as an ISO
value. The higher the ISO value, the more
sensitive a camera should be. However,
when reviewing a marketing datasheet or
brochure for a given camera, any
information regarding light sensitivity
should be regarded with a degree of
skepticism. There are standards – such as
ISO 12232 Ssat – that define how to
measure light sensitivity, but many highspeed
camera vendors do not adhere to the
standards when they measure the ISO
values of their cameras. Other vendors
publish ISO values for their cameras but
do not specify exactly which ISO standard
(ISO 12232 Ssat, for example) the values
conform to. Without such information the
ISO values are meaningless.
It is important to note that there are
many ways to make a camera appear to be
more sensitive than it actually is. Two
common approaches are to increase
gamma and/or increase gain. Such
practices will result in a lower level of
image quality, but this might not be
immediately obvious in a quick product
demonstration by a clever sales guy.
The bottom line regarding light
sensitivity is that an on-site evaluation
should be conducted prior to the purchase
of any high-speed camera to make sure
that it provides the image quality and light
sensitivity required for a given application.
If cameras from different vendors are
under consideration, then a side by side
test of those cameras is essential.
MINIMUM EXPOSURE TIME
A camera’s minimum exposure time is
often a critical factor in choosing a highspeed
camera. Some very fast high-speed
events require extremely short exposure
times – sometimes even less than 1
microsecond – to stop the motion of those
high-speed events. A camera’s ability to
achieve a sub-microsecond exposure is
dependent upon two things. First, the
camera’s sensor must be capable of
performing such a short exposure. Second,
the camera’s sensor must be sensitive
enough that when it does utilize a submicrosecond
exposure it can capture
enough photons of light during the
exposure to be able to generate video that
is of sufficient quality for analysis. A short
exposure does no good if the end result is
3
86 SHOWCASE 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
a sequence of images that are so dark that
it is impossible to see what happened.
RESOLUTION
Another consideration in the purchase of a
high-speed camera is pixel resolution.
High-speed cameras are available in a
variety of resolutions. Most often the
resolutions are between 1-megapixel and
4-megapixel. Higher resolutions are
important when the field of view of the
camera is very large, or when a very small
spatial resolution is required because there
are a lot of fine details or small items
within the high-speed event that need to
be studied.
It is important to understand that the
higher the resolution of the camera, the
lower the maximum frame rate will be.
With a 4-megapixel camera there are 4x
more pixels to process than with a
1-megapixel camera. Therefore, it is not
possible to achieve the same frame rates
with a higher resolution camera than with
a lower resolution camera.
It is also important to understand
that, in general, the higher resolution
cameras are less sensitive than the lower
resolution cameras because their sensors
have smaller pixels.
When purchasing a high-speed camera
to be used for aerospace applications, a
camera’s frame rate, light sensitivity,
minimum exposure time and pixel
resolution are among the most important
factors to consider. Aerospace testing
environments can be very challenging for
high-speed camera suppliers. To guarantee
the successful implementation of highspeed
cameras within such environments
it is important to select an experienced
supplier who can provide a range of highly
reliable cameras as well as exceptional
customer support. Photron is one of the
most trusted high-speed camera suppliers
in the world, offering outstanding
customer support on every continent.
Photron’s FASTCAM Series consists of a
wide range of cameras that have been
designed to function effectively within the
aerospace industry. \\
Tim Callenbach is the director of sales and
marketing at Photron USA.
3 // High-speed cameras
can be used for Particle
Image Velocimetry,
revealing fluid flows in
airplane engines
/AEROSPACETESTINGINTERNATIONAL.COM