IEEE Spectrum November, 2016 - 38

Standard image

Controlled depth of field

70 mm

would also gain the ability to zoom in
and out. And if we arranged the multiple camera modules to create what
was effectively a larger aperture, the
photographer could control the depth
of field of the final image.
While at that point I knew it was theoretically possible to use multiple modules to overcome the shortcomings of
a small camera, I needed to confirm
that such a strategy was truly practical. So I figured I'd better check with
some optics experts. In the first half of
2013, I cold-called Julie Bentley, a lensdesign expert at the University of Rochester, in New York, and drove 5 hours
from where I was living in New Jersey
to meet with her.
It started as a contentious conversation: She basically told me I was
crazy. But she kept asking questions. I
answered them, apparently convincingly, because after about 45 minutes,
she became supportive of the approach
I was proposing and sent me to Moondog
Optics in Fairport, N.Y., a company that
does optical design. I met with the CEO,
Scott Cahall, who thought what I was
suggesting was doable.
38

NOV 2016

NORTh AMERICAN

150 mm

ChoICES, ChoICES: Though the individual camera modules have fixed
focal lengths and aperture sizes, combining the images from the lenses in
different ways allows photographers to change the depth of field and zoom
using the focal-length equivalents of 28 mm through 150 mm.

And so later in 2013, I joined with
Dave Gra n n a n, who h ad ju st lef t
Nuance Communications, and officially
started Light.
the first and current version of the
Light camera-called the L16-has 16 individual camera modules with lenses of
three different focal lengths-five are
28-mm equivalent, five are 70-mm equivalent, and six are 150-mm equivalent.
"Equivalent" means that the lens
achieves the same field of view as a lens
of the specified focal length in a conventional film camera. For a simple singlelens element, when light comes from far
away and hits the lens, it converges at a
point. The focal length represents the
distance of that point from the lens. For
example, the equivalent focal length of a
human eye is around 50 mm. A lens with a

SPECTRUM.IEEE.ORG

larger focal length has a higher magnification and makes the subjects appear larger.
All the lenses in the L16 are molded
plastic, and all the camera modules
capture images using standard CMOS
sensors, similar to those used in smartphone cameras. Each camera module has
a lens, an image sensor, and an actuator
for moving the lens to focus the image.
Each lens has a fixed aperture of F2.4-
that is, the focal length of the lens divided
by its diameter is equal to 2.4. (A lens
with a lower F number has a larger aperture and so lets in more light.)
Five of these camera modules capture
images at what we think of as a 28-mm
field of view; that's a wide-angle lens on
a standard SLR. These camera modules
point straight out. Five other modules
provide the equivalent of 70-mm telephoto lenses, and six work as 150-mm

LighT

28 mm

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