Practical Photography - May issue

Know Your Stuff
What do I need to know
when buying a new lens?
I’m about to invest in
a second lens for my
DSLR. Do you have
any need-to-know advice
before I make my decision?
Stuart Granger, Leeds
Dan says: If you only own
one lens, chances are it’s the
18-55mm standard zoom that
came with your camera. While
these basic kit lenses tend to
offer reasonable image quality,
they often lack in other key
areas, including build quality
and low light performance. If
you’re thinking of investing
in some new glass, either as
an upgrade to your kit lens or
to extend your focal range,
it’s well worth knowing your
aperture blades from your
autofocus before you commit.
The very first thing
you’ll need to decide is what
focal length best suits your
photography. This will largely
depend on what you shoot.
Portraits, for example, are
usually well suited to 50mm
lenses (85mm on full-frame),
whereas landscapes are
normally shot at around
14mm (20mm on full-frame).
The next thing to consider
is the maximum aperture.
If you want a very blurry
background behind your
subject, or if you shoot
handheld in low light, you’ll
want an aperture of around
f/2.8 or wider. However, if
you’re a landscapes shooter,
this is less important as you’ll
mostly be shooting at f/16.
TIP
CONSIDER
SECOND HAND
Used lenses are generally as
good as new ones, so long as
there aren’t scratches on the
front or rear elements, or
internal dust or
mould.
Once
you’ve
settled on these two things,
you should have narrowed
down your options to just a
few compatible models. But
before you decide, it’s worth
considering some of the below
features and functionality.
Know your lens...
Lens coatings
The elements on modern lenses have special
coatings to reduce internal reflections, which
suppress flare and ghosting. These usually have
technical-sounding names like SubWavelength
Structure Coating or Nano Crystal Coating, but
essentially they all do a similar thing. Look for
examples online of whether a specific lens
controls flare well.
Smooth
zoom and
focus rings
If you get the chance to
handle a lens before
you buy it, be sure to
check the action on the
zoom and aperture
rings. You’re looking for
smooth, consistent
movement with a small
amount of resistance.
Avoid sticky or uneven
operation at all costs,
not least because of
what this says about
the lens’ build quality.
Lens hood
When shooting into bright sunlight, lens
flare can be an issue, causing very low
contrast images. A lens hood can help
protect against this, and they’re also useful
for keeping raindrops off the front element.
Lens hoods aren’t always included with
cheaper lenses, so check this out before
you buy.
Internal design
All lenses contain a series of glass
elements, the arrangement and shape
of which affect distortion and chromatic
aberration. Look out for lenses with
aspherical elements, which are
expensive to produce but control optical
imperfections well. Also, check how
many diaphragm blades your lens has
– the more there are, the more
circular the bokeh will be.
Extending barrel
On cheaper lenses, the end of the barrel
usually extends when focusing and/or
zooming, which can leave the optics open
to dust contamination. If you can, look out
for a lens where this movement is internal
and the length of the lens always remains
constant, regardless of focal length or
focus distance.
Size & weight
If you’re an outdoor or travel
photographer, having to lug heavy kit
across large distances can be a real
problem. For this reason you might
value portability above all else and opt
for a superzoom or pancake lens, or
invest in a CSC system, for which
lenses tend to be smaller and lighter.
Don’t forget though that wide aperture
lenses are generally heavier.
Weather-sealing
Image
stabilisation
Some lenses come
with optical
stabilisation, where tiny
stepping motors move
a group of elements to
compensate for
camera shake. This
generally allows you to
shoot with shutter
speeds 4 stops slower
and still get sharp
results. Stabilisation is
more commonly found
on zooms than primes.
If you use your camera outdoors
regularly, it might be worth considering
a fully weather-sealed lens, which
means a number of rubber seals stop
any dust or water from getting in. This
should allow you to work comfortably
in heavy rain or on a sandy beach,
without the risk of any damage.
110 PRACTICAL PHOTOGRAPHY