https://www.economist.com/science-and-technology/2021/04/14/taking-selfies-with-a-liquid-lens

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[20210417_stp503]

Photography
Taking selfies with a liquid lens

A smartphone with a fluid lens

Science & technologyApr 17th 2021 edition
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Apr 14th 2021

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SERIOUS PHOTOGRAPHERS are usually laden with serious amounts of
serious kit, especially multiple lenses. The paparazzi use zoom
lenses to get a telescopic view of their subjects. Mid-range lenses
are well-suited to street-scenes and portraits. Wide-angle lenses are
good for capturing sweeping cityscapes. A macro lens is ideal for
close-ups. But what if it were possible to build a single lens that
could cover all such eventualities? Xiaomi, a Chinese electronics and
consumer-goods company, is taking a shot in that direction.

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On April 16th, Xiaomi's new Mi Mix Fold smartphone will go on sale,
priced from 9,999 yuan ($1,526). Like most new smartphones it is
packed with whizzy features, including a flexible screen that can be
folded open and shut. But what makes this new phone special is that
it is the first to come equipped with a liquid lens.

A conventional camera lens consists of several specially shaped and
polished glass or Perspex elements inside a tube. These act to
deflect incoming light. By moving them closer or farther away, it is
possible to focus an image onto the camera's sensor and, if it is a
zoom lens, to adjust the magnification. In modern cameras the lenses
are moved by electric motors.

There is little or no such paraphernalia involved with liquid lenses.
They work a bit like the human eye, in which muscles squash or
stretch an elasticated lens, altering its curvature so that a person
can focus on objects at different distances. Most liquid lenses
consist of an aqueous fluid, sometimes with an associated layer of
oil, sitting on a water-repelling surface. This surface causes the
fluid to form into a spherical blob, like a bead of water sitting on
a lily pad. Applying an electric charge to the edge of the blob
attracts molecules in the liquid to the perimeter. This flattens the
lens, thus changing its focal length. Conversely, reducing the charge
sends the molecules back to the middle, causing the lens to fatten up
again.

Liquid lenses of this type already have a number of uses, mostly in
industry and medicine. Because they can focus rapidly on objects at
different distances and tend not to wear out, they are sometimes
employed as image sensors on automated production lines, and to read
bar codes. They can also be made tiny, which means they are ideally
suited for use with the laparoscopic cameras that are inserted into
people's bodies during keyhole surgery.

Xiaomi, however, has taken a different direction in its new phone. It
uses a thin, solid film to contain the lens fluid and a small,
high-speed electric motor to stretch or relax this film in order to
change the lens's curvature. The company says its lens can work as a
3x optical zoom (a figure that rises to 30x with "digital
enhancement") and as a macro lens, focusing down to 3cm for taking
close-up shots.

The company has not explained why it has taken this route with its
liquid lens. Perhaps it is more familiar with the technology
involved. Nor is it risking putting all its eggs in one basket, as
the new phone is also equipped with a standard lens and an ultra
wide-angle one. As it will be sold only in China it is, perhaps,
partly experimental. Xiaomi did not respond to a request for more
information.

As other smartphone-makers have been investigating the technology, it
seems only a matter of time before liquid lenses replace some or all
of the multiple lenses now appearing on phones. And with phones
rivalling even some high-end cameras in picture quality, the makers
of conventional cameras might follow with liquid lenses of their own.
Snappers, then, can look forward to their gadget bags getting a good
deal lighter.#

A version of this article was published online on April 14th, 2021.

This article appeared in the Science & technology section of the
print edition under the headline "Liquid selfies"

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