D
82 http://www.digitalcameraworld.com
CANONSCHOOL
espite the numerous
advances made in
forward-thinking
lens technology, chromatic
aberration, or colour
fringing, remains a constant
problem for photographers.
This optical phenomenon is
very similar to the kind of
effect you see when light is
refracted through a prism.
Different wavelengths of
light are separated as they pass
through the elements in a lens
and they are unable to be
focused at the exact same
point on the camera’s
imaging sensor.There are actually two
different types of chromatic
aberration that you’re likely to
encounter when out shooting:
lateral and axial. Lateral
aberration is commonly seen
in wide-angle lenses, and
produces colour fringing, or
halos, around certain high-
contrast objects (look for it
along the contours of tree
branches, or buildings that are
framed against a bright sky).
Telephoto lenses are much
more likely to show axial
aberration, which will manifest
itself as blurred colours in front
of and behind the parts of thephotograph that are in focus.
With both of these aberrations,
the results essentially end up
being the same: the image will
look less sharp and a little bit
more unsightly.
Ideally, enabling chromatic
aberration correction should
be able to actually correct this
in most cases. If for somereason you can’t see this
option in the menu, that’ll
either be because your
camera, unfortunately, does
not offer this function (as is
the case of the 1300D, 2000D
and 4000D), or the Digital
Lens Optimizer is enabled
(on certain compatible
cameras, of course).Chromatic aberration
correction
Remove fringing from the edges of objects
Avoiding soft shots
Use diffraction correction to bring back the bite
THE SMALLEST aperture available
on a lens – which is typically either
f/22 or f/32 – delivers the most
extensive depth of field, or
front-to-back sharpness. This can
be important when it comes to
landscape and macro pictures,
where you often want to capture
the maximum amount of detail. But
although a small aperture appears
to bring much of a scene into focus,
it doesn’t give the sharpest results.
The reason for this is an optical
effect called diffraction. This occurs
when the light waves entering the
lens are bent by the hard edges of
the aperture. Meaning they are
unable to converge correctly
when they hit the image sensor.
Diffraction actually happens at
all aperture settings, but it’s more
visible at small apertures. This is
because the proportion of light
waves affected increases as the
hole in the lens decreases in size.
The result is the fine details and
edges in an image will appear soft.You can, of course, simply avoid
small apertures altogether, or
simply ramp up the amount of
digital sharpening, but neither is
ideal. Diffraction correction,
however, allows you to counteract
the softening without having to
sacrifice depth of field.
Until a few years ago, diffraction
correction was part of Digital Lens
Optimizer (DLO) and unavailable as
a standalone feature, but now most
EOS bodies list it separately. That
being said, it isn’t displayed in the
lens aberration correction
sub-menu of some cameras
unless DLO is deactivated.
There are some caveats to using
diffraction correction... As with
peripheral illumination correction,
it can make picture noise somewhat
more obvious, and the correction
effect at higher ISO speeds isn’t as
strong as it is at lower ISOs. It’s
also not possible to use it when
recording movies (in fact,
it won’t even be displayed).COLOUR FRINGING
Before^
After^