sensor size (mm)
Figure 1.2 Fundamental Parameters
imaging resource guide imaging lenses filters microscopy cameras illumination targets
EO Best Practice #4: Light up your life.
It really does matter.
While it can seem like an art form, selecting the appropriate lighting
geometry is highly scienti c. In order for a lens and sensor to e ectively
work together, strong contrast must be produced by properly
lighting the object. The characteristics of the object under inspection
and the nature of any defects must be understood so that the proper
illumination geometry is used. Keep in mind that sometimes these
lights can be very large (see EO Best Practice #1). Learn more about
illumination geometries on pages 158-161.
E O Best Practice #5: Color matters.
The wavelength (color) selected for the illumination can have an
enormous impact on improving or reducing system performance. For
instance, in an application using both high quality optics and a top-ofthe
line sensor, switching from broadband to monochromatic illumination,
or between speci c wavelengths, can improve performance by
a signi cant amount. As with EO Best Practice #4, the proper choice
of wavelength can make the di erence between high contrast and no
contrast. Depending on whether the wavelength is correctly chosen
or not, the color of illumination can determine the success or failure
of a system. Learn how proper ltering techniques can have an impact on
system performance on Pages 128-130
E O Best Practice #6: There can be only one; high
resolution and large depths of fi eld struggle to co-exist.
As shown in Section 2.4, maximizing resolution and depth of eld requires
the same variable, the lens’s f/#, to move in opposite directions.
Essentially, it is impossible to have very high resolution over
a large depth of eld. Physics dictates that this cannot be done and
compromises will need to be made or more elaborate solutions, such
as using multiple imaging systems, will need to be employed.
E O Best Practice #7: There is no universal solution;
a single lens that can do everything does not exist.
As resolution requirements increase, the ability to decrease aberrations
(attributes of optical design that adversely a ect performance) becomes
increasingly di cult over a wide range of working distances and elds of
view. Even without budget constraints, there are limitations. For this reason
a wide range of lens solutions for similar applications are required.
More details are in Section 3, pages 18-21 on Designing for Performance.
E O Best Practice #8: Be self-aware. Thoroughly
understand the object to be inspected.
The foundation of imaging is the ability to produce the highest level
of contrast possible on the object under inspection, so an understanding
of the object’s properties, such as its materials or nishes, is critical
to the application’s success. Additionally, it is not enough to just
know what parts are considered good or bad. Rather, to guarantee
high levels of reliability and repeatability, the range of details that will
be inspected and the margins for good and bad must be understood.
E O Best Practice #9: Be a control freak.
The ability to control the environment into which the imaging system
is deployed can signi cantly a ect the reliability and consistency
of results. Additionally, it also reduces the likelihood of unintended
problems. Whether using lters to increase contrast, ba es to eliminate
unwanted light from entering the system, or measurement devices
to monitor light sources for spectral stability, controlling the
environment will reduce unforeseen di culties in the future. Some of
these techniques are extremely low cost ways to protect and increase
the performance of an expensive imaging system.
E O Best Practice #10: Be the squeaky wheel.
Do not be afraid to ask why something will or will not work. Suppliers
should be able to explain why di erent components in the system
are or are not capable of achieving the desired result. The answer will
not always be the same; sometimes the issues are laws of physics limitations
and sometimes they are de ciencies related to the design or
fabrication of the component. Optical manufacturing is a science, and
the designers and manufacturers should be capable of explaining why
things are happening.
E O Best Practice #11: Make a list; understand and defi ne
the fundamental parameters of the imaging systems.
By narrowing down the speci c parameters required for the imaging
system, the wide range of available lenses and sensors can
be reduced to a manageable selection
of components. Fundamental parameters
of an imaging systems are a great
place to start and are detailed in the
Section 1.2: Fundamental Parameters
of an Imaging System
The following parameters are the most basic concepts of imaging and
will be referenced throughout the remainder of this guide.
Field of View (FOV): The viewable area of the object under inspection.
This is the portion of the object that lls the camera’s sensor.
Working Distance (WD): The distance from the front of the lens to
the object under inspection.
Resolution: The minimum feature size of the object that can be distinguished
by the imaging system. Learn more in Section 2.1.
Depth of Field (DOF): The maximum object depth that can be
maintained entirely in acceptable focus. DOF is also the amount of
object movement (in and out of best focus) allowable while maintaining
focus. Learn more in Section 4.4, page 30.
Sensor Size: The size of a camera sensor’s active area, typically speci ed
in the horizontal dimension. This parameter is important in determining
the proper lens magni cation required to obtain a desired eld of view.
PMAG: The Primary Magni cation of the lens is de ned as the ratio
between the sensor size and the FOV.
fi eld of view (mm)
Note: Typically, only horizontal values are used.
Field Of View
Figure 1.2: Illustration of fundamental parameters of an imaging system.