Section 4: Real World Performance
22 +44 (0)1904 788600 • EDMUND OPTICS® imaging lenses filters microscopy cameras illumination targets imaging resource guide
Section 4.1: From Lens to Sensor:
Limitations on Collecting Information
In an e ort to better understand the di erences that can occur between
theoretical and as-manufactured performance, Examples 1-3 show what
happens at the sensor level, and how output from the sensor would be
visualized with di erent wavelengths and f/#s. Figures transition from
theoretical to real world examples that include aberration and lens
As will be noted, the shorter the wavelength, the
theoretically greater the performance of the imaging
system. In recent years, blue LEDs have become
very dependable for increasing the performance of
small pixel-equipped sensors. Remember EO Best
Practice #5, (page 9) Color Matters. Understanding
the physical capabilities and limitations of a lens at different
f/#s and wavelengths helps the user optimize the
utility of high resolution imagers and enables solutions to once
di cult applications.
E xample 1: Variation in Spot Sizes and Pixel Outputs
with Wavelength at Low f/# (Theoretical)
Figures 4.1a and 4.1b demonstrate four di erent wavelengths being
perfectly imaged, with the exception of blur caused by di raction
(Section 3.1), in the center of a sensor containing 3,45 μm pixels and
at f/2,8. This is considered a small pixel size, and it is associated with
a very popular 5 megapixel sensor utilized by many camera companies.
Figure 4.1a shows the di erence in spot size when stepping up
from 470 nm (Blue) to 880 nm (NIR) wavelengths. Figure 4.1b shows
pixel outputs for each of the images created by the lens in Figure 4.1a;
notice the smaller spots associated with the shorter wavelengths.
E xample 2: Variation in Spot Sizes and Pixel Outputs
with Wavelength at High f/#s (Theoretical)
The images in Figure 4.2 are similar to Figure 4.1, but the aperture
setting has been changed to f/8. At this setting, Figure 4.2a shows
that all of the spots, regardless of wavelength, exceed the size of a
single pixel, which causes energy to spill into adjacent pixels. Figure
4.2b shows a noticeable blurring in the pixel outputs at the longer
wavelengths with spots at 880 nm no longer able to be separated. This
demonstrates the physical rami cations associated with changing the
f/#, even in a theoretically perfect system.
Figure 4.1a: An Illustration of how spot size changes by wavelength from
470 nm (blue) to 880 nm (NIR) at f/2,8.
470 nm 520 nm 660 nm 880 nm 470 nm 520 nm 660 nm 880 nm
Figure 4.1b: How the pixels of a sensor interpret the spot sizes in fi gure 4.1a.
Figure 4.1: Variation in spot sizes and pixel outputs with wavelength
at low f/#.
Figure 4.2a: An Illustration of how spot size changes by wavelength from
470 nm (blue) to 880 nm (NIR) at f/8.
Figure 4.2b: How the pixels of a sensor interpret the spot sizes in fi gure 4.2a.
Figure 4.2: Variation in spot sizes and pixel outputs with wavelength
at high f/#.