58 DIGITAL CAMERA^ APRIL 2020 http://www.digitalcameraworld.com
CAMERA COLLEGEto physically move a floating group of
elements within the lens in order to
counteract the movement of the camera.
Today’s lens-based stabilisers usually
give you around four or five ‘stops’ of shake
compensation. This means that the system
can allow you to shoot at a shutter speed
that’s four or five stops slower than
recommended for a given exposure, and
still get sharp handheld results. This is
great news if you find yourself shooting
in relatively low light without a tripod, or
when you want to use a smaller aperture to
increase the depth of field – two situations
where you may end up with soft pictures
because the resulting shutter speed would
be too slow. Of course, image stabilisation
is only good for reducing the blur causedby fairly small camera movements, and
has no effect on motion blur caused by
the movement of the subject; to cure
that problem, you’ll still need to use
a relatively fast shutter speed.
In-camera stabilisation, also known
as ‘sensor shift’ or IBIS (In-body Image
Stabilisation), achieves a similar result
by moving the image sensor inside the
camera. This is typically achieved with
electromagnets and a floating sensor,
with some cameras offering five-axis
adjustments to cancel out both horizontal
and vertical shift, horizontal pan (yaw),
vertical tilt (pan) and rotational movements
of the camera. IBIS only makes practical
sense in a mirrorless camera, as you are
able to monitor the effects of theImage stabilisation can
be broadly broken down
into three categories:
in-lens, in-camera,
and electronicHow a lens stabiliser works
It adds weight and cost to a lens,
but a built-in stabilising unit
offers the potential for more
a more sophisticated level
of shake reductionLenses that offer built-in image
stabilisation have a floating group
of elements within the lens barrel that
are shifted in the opposite direction to
detected vibrations. Gyroscopic sensors
continuously measure the angle and
speed of the vibrations, feeding this
data back to the lens’s onboard
microcomputer, which then calculates
how much the stabilisation elements
need to be adjusted.
Of course, all this functionality adds
complexity to the lens design, and this
can have a detrimental effect on the size,
weight and cost – and potentially image
quality, too. That being said, there are
some notable advantages of having a
dedicated image stabilisation unit in
individual lenses. The performance can
be tailored to specific focal lengths, for
example, and achieving a stable image
outside of the camera means that the
effect is visible in the optical viewfinder
of a DSLR – something that isn’t possible
with sensor-based stabilisation. Having
a jerk-free display means that it’s both
easier to compose shots and for the
camera’s autofocus system to keep
objects in focus, although it can take
a little while to grow accustomed to the
‘floaty’ viewfinder image that you get
when image stabilisation is active.Sensors
Canon’s RF 24-70mm f/2.8L IS USM
features two gyro sensors that detect
camera shake, and a microcomputer
that drives the stabilisation unit. This
lens also features Dual Sensing IS, where
the camera’s processor takes over and
crunches data from both the gyros and
the camera’s imaging sensor, for more
accurate control over stabilisation.Canon