f/# of lens
Sensor Format: ¼” ” ½” ”
0.00 2.75 5.50
Image Height (mm)
typical sensor heights
Figure 2.8a: A relative illumination curve shows the relative brightness
vs. field height at various f/#s.
Relative Illumination: f/1,4, 2/3" Sensor Format
Distortion vs. Image Height
-2.0 0.0 2.0
Image Height (mm)
imaging resource guide imaging lenses filters microscopy cameras illumination targets
DOF: 20 lp/mm, f/2.8, 500mm Focus
f/#, and working
used for curve
0.0 500.0 1000.0
Working Distance (mm)
Center of axis represents
balanced best focus.
The Relative Illumination curve is used to quantify changes in the illumination
level across the sensor. Changes in illumination can have
undesired effects on the final image when it comes to analysis. Details
on what causes RI changes can be found in Section 4.2 on Relative Illumination.
The curve in Figure 2.8a shows a typical relative illumination
curve, with the relative brightness (relative to the brightest point in the
image) vs. field height.
The different individual curves represent the relative illumination
performance based on f/#. Note that as the f/# increases, relative
illumination generally increases. Be careful not to confuse this with
absolute brightness, as higher f/#s will still cause an overall brightness
decrease. Learn more about f/# in Section 2.4.
The x-axis represents the distance from the center of the sensor
to the corner of the sensor. The y-axis indicates how much illumination
exists at any position in the field relative to the point of highest
illumination, typically the center of the field, set equal to 100%. In
order to clarify how the lens's relative illumination will perform across
different sensors, dotted lines representing different sensor diagonals
have been included in the plots. Figure 2.8b is a projection of how the
relative illumination in Figure 2.8a will look at f/1.4 in a real world image.
Learn more about relative illumination in Section 4.2, page 24.
In an imaging system, distortion causes apparent magnification
changes with respect to field position. There are many ways to represent
distortion, but Figure 2.9 shows field height vs. geometric distortion
percentage, which is a typical plot that lens designers and engineers
utilize to characterize distortion. Lean more about distortion in
Section 4.5, pages 33-34.
The plot in Figure 2.9 shows distortion as the percentage of magnification
shift (x-axis) moving from the center of the image to the
corner of the image (y-axis). The larger the absolute percentage of
distortion, the larger the difference between the ideal image map and
the distorted one.
Figure 2.8b: This plot shows how the f/1,4 curve blue in 2.8a will
appear across a 2/3” image sensor.
Figure 2.9: A distortion curve illustrates the magnification shift from
the center of the image to the edge.
Figure 2.7: Depth of field performance curve shows how
contrast changes with working distance.
Our curves are shown for one point in space and
performance will vary at other points. Please contact
EO Technical Support for details relating to your application.
+44 (0)1904 788600 or email: email@example.com