IEEE Spectrum November, 2016 - 37

Top: Rajiv LaRoia; BoTTom: TekLa S. peRRy

know much about optics. The solution,
I later realized, straddled both the digital and the optical worlds. And I had the
luxury of being able to sit at home and
teach myself optics for a year.
I had only a rough idea of how the
problem might be solved at that point.
But as I dug in, I realized not only that
there might be a technical solution but
also that this was the perfect time to try
to build a different kind of commercially
viable camera.
I knew that cellphone camera lenses
were molded out of plastic-that's
why they were so inexpensive. And
thanks to cellphones, molded plastic lens technology had been nearly
perfected over the previous five years
to the point where these lenses were
"diffraction limited"-that is, for their
size, they were as good as the fundamental physics would ever allow them
to be. Meanwhile, the cost had dropped
dramatically: A five-element smartphone camera lens today costs only
about US $1 when purchased in volume.
(Elements are the thin layers that make
up a plastic lens.) And sensor prices had
plummeted as well: A high-resolution
(13-megapixel) camera sensor now costs
just about $3 in volume.
W h i le sm a r t phone le n s e s h ave
become extremely good, the quality
of the smartphone camera today is
nowhere comparable to that of a highend DSLR. There are four main reasons:
First, the lenses of smartphone cameras are small and collect very little
light. And you can't produce good pictures without capturing enough light
energy. So smartphone photos will
often be "noisy" or grainy, particularly
in low light. Second, small sensors and
a high pixel count mean that the individual pixels are tiny (approximately
1 micrometer across), and therefore
hit a saturation point after receiving
just a little bit of light. This results in
pictures with very limited dynamic
range (limited differences between the
darkest darks and the lightest lights).
Third, smartphone-camera lenses have
a fixed focal length and so can't zoom.
Finally, because of the small lens aperture, smartphone pictures have a very

PUZZLINg IT oUT: Fitting the 16 cameras [above] into a box of a reasonable size turned out
to be a challenge. Light founder Rajiv Laroia [opposite] did paper sketches and then tried to
figure it out on a computer-assisted-design system. Eventually, he cut out bits of paper [top]
and worked with them as if they were part of a jigsaw puzzle.

large depth of field-that is, they are
sharp over a very large range of subject
distances from the camera. That might
sound like a good thing, but it's not,
because controlling the depth of field
is essential for artistic photography.
I thought that all these shortcomings
of smartphone cameras might be overcome by using multiple smartphone
camera modules to take multiple pic-

tures simultaneously, which could then
be combined digitally. By using many
modules, the camera could capture
more light energy. The effective size of
each pixel would also increase because
each object in the scene would be captured in multiple pictures, increasing the dynamic range and reducing
graininess. By using camera modules
with different focal lengths, the camera

SPECTRUM.IEEE.ORG

NORTh AMERICAN

NOV 2016

http://SPECTRUM.IEEE.ORG

Table of Contents for the Digital Edition of IEEE Spectrum November, 2016