pupil enlarged and observe its response
to light variations; and they could
observe and handle various modes of
protection against extreme radiation
intensities (e.g., welding glasses and
high-optical-density filters for looking
at the sun).
Object size and distance
The visitors peered through a microscope
and telescope. They learned how the
development of these instruments has
influenced microbiology and astronomy.
In one experiment, visitors could not
only see the tiny blood vessels in their
own retinas but also the blood cells
within those vessels.
Defective color vision
Not everyone perceives color in the
same way. To experience this, the visitors looked through special glasses that
simulated anomalous color vision. They
could also take a color-anomaly screening test. These were among the visitors’
favorite experiments; they were eager
to experience how color-blind people
perceive the world.
Color constancy
What happens if we use a digital photographic camera to capture images of
surrounding scenes? Does it behave in
a manner that is similar to the human
visual system? Illumination may be a
fundamental factor that determines
how we perceive objects. For instance,
meat or fish may look appetizing or not
depending on the lighting in the room.
To demonstrate this, we showed the visitors pictures of the same objects taken
under different lighting conditions. We
also asked visitors to observe objects
under various colors of illumination. We
discussed the differences and explained
why white balancing is necessary for
digital cameras.
Polarization
Humans are not able to determine the
state of polarization of light entering
their eyes. But we can see which areas of a
transparent rigid object are under stress if
we use a polariscope. This device is based
on the photoelasticity phenomenon.
Speed
The exhibit explored how fast our
visual system can react to temporal
changes through an experiment with
a stroboscope, in which visitors can
“freeze” a rotating wheel. It also
explained the phenomenon of visual
persistence—which refers to the
amount of time that the retina retains
information it has been stimulated with;
visual persistence limits how fast our
visual system can react to changes.
3D Vision
Why do we have two eyes? In this portion of the exhibit, visitors explored
depth perception and 3D vision. They
used stereoscopes to view anaglyphs and
holograms of images shot in Granada
more than 120 years ago.
In addition, the exhibit included a
comparison between the human visual
system and that of other animals. Different animals have varying spectral
ranges, intensity thresholds and visual
acuities that are tailored to their unique
environments. Cats and other nocturnal
vertebrates, for example, have a layer of
tissue near the retina that reflects more
visible light into the retina, allowing
them to hunt their prey at night.
The exhibit was initially planned to
last three months, but it was recently
extended for three additional months due
to the enthusiastic reception among visitors. It is slated to end in September 2009.
We are very satisfied with the exhibit
and glad that it has been a useful tool for
bringing people closer to optics. t
The authors thank their colleagues from
the optics department at the University of
Granada who helped prepare the exhibit,
including Javier Romero, Eva Valero,
Rafael Huertas, Clara Plata, Luis Gómez-Robledo, Rafael Roa and Enrique Hita.
Javier Hernández-Andrés ( javierha@ugr.es),
José A. García and Juan L. Nieves are with the
optics department at the University of Granada
in Spain.
MotionControl_09.qxd 4/6/09 5:51 PM Pa
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