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What's New With Zooms
The latest in lens technology
By Maura C. Lanahan
Lugging around a weighty pack
loaded with equipment isn’t the ideal way to experience
nature, and hiking long treks with it on your back or shoulders
can lead to injury. You don’t want to leave gear behind,
but you definitely don’t want to risk ruining the day or
your health with a cumbersome load. I’ve limited my equipment
to include only the necessities, and zoom lenses have become
an essential part of my gear.
There’s a convenience factor in using a zoom lens. If you’re
on a hike and out shooting for a long day, the last thing you
want to do is carry a bunch of lenses. They can add a lot of
weight to your bag and take up limited real estate that could
otherwise be reserved for useful gadgets and tools.
There’s a quality advantage, too. It used to be that a
zoom lens’ true asset was simplicity. The range of focal
lengths that were offered in older zooms was useful, but unfortunately,
the high quality and sharpness that fixed or prime lenses provide
wasn’t matched. This isn’t the case today. Optics
technology, lighter materials and advanced designs have brought
the quality and convenience factors together.
Focal Length
When choosing a zoom lens, first consider what you’ll
be shooting. One lens may suit all of your photographic needs,
so you can end up saving some money as well as free yourself
from the burden of extra gear.
Wide-angle zoom lenses are perfect for showing the expanse
of a landscape or placing flowers or rocks in your foreground
with a huge sky as a backdrop. Newer wide-angle zooms have
become even wider due to the advent of small digital-format
D-SLRs—your D-SLR with a full-sized 35mm sensor will
provide an even wider angle of view. The standard wide-angle
zoom is in the 16-35mm range, but small-format digital lenses
equal that angle of view with a 10-22mm range.
Mid-range wide-to-telephoto lenses have become popular due
to their resourcefulness. The wide focal length can capture
the span of an area and is useful if you have to shoot in
tight spaces, while the telephoto end provides you with a
portrait lens, which is ideal for isolating foliage or flowers.
I’ve seen a lot of photographers stick with just this
one lens because it offers them all the focal lengths they
need. Mid-range wide-to-telephoto lenses commonly have focal
lengths of approximately 28-80mm or 100mm. Small-format lenses
offer the equivalent in focal lengths of about 18-55mm.
Extreme-range wide-to-telephoto zooms are relatively new.
These lenses typically go from 28-300mm (18-200mm in small-format
digital). They offer a very large range, although size and
lens speed can be compromised.
Telephoto
A standard mid-range telephoto zoom lens is effective not
only for landscapes and macro photography, but for hiking
as well. Mid-range zooms give you enough of a zoom to magnify
and compress your scene, but they’re small and light
enough to carry and place on a light tripod without dragging
it down. Standard mid-range telephoto focal lengths typically
are 70mm to 210-300mm.
If you plan on photographing wildlife, you’ll need a
telephoto zoom. Focal lengths of these lenses range from at
least 100-400mm or 200-400mm. They afford you the ability
to photograph animals at a distance without disturbing them
in their natural habitat. Telephoto zooms are heavy lenses,
as they incorporate a lot of glass to achieve their focal
length, so you’ll likely need a tripod.
Maximum ƒ-Stop
You may be shooting images in low light, requiring a lens
with a large maximum ƒ-stop. A fast ƒ/2.8 lens is
ideal for photographing subjects in dimly lit situations like
dusk or dawn, or any other low-light setting where you don’t
want to use a flash. A lot of photojournalists need a lens
with a large maximum ƒ-stop because it allows them to
handhold their camera, which is an asset when street shooting.
This also can apply to wilderness shooting where trees can
limit light. Especially with long zoom ranges, you should
notice if a zoom lens’ maximum aperture changes. A variable-aperture
lens has different maximum apertures at different focal lengths.
So when you zoom out, the aperture changes to a smaller one
and, consequently, the shutter speed has to slow down to achieve
the correct exposure. For example, a 28-200mm lens might be
ƒ/3.5 at 28mm, but ƒ/5.6 at 200mm. This may not
matter to you if you’re using a tripod, but it’s
something to consider if you’re handholding your camera.
Special Glass
When standard optical glass is used in telephoto zoom lenses,
chromatic aberration can occur. Also referred to as color
fringing, chromatic aberration is the inherent tendency for
glass to disperse a ray of light into the colors of the rainbow.
This effect usually is visible where the lighter parts of
your scene meet the darker parts, such as tree branches against
a bright sky.
These aberrations or color fringes can be especially noticeable
if you blow up your picture beyond 8x10 inches. To eliminate
chromatic aberration, many manufacturers employ special glass
in their lenses to correct for it. Low-dispersion (LD), extra-low-dispersion
(ELD) and special low-dispersion (SLD) glass and apochromatic
lenses (APO) help to refocus the dispersing light waves together
so they meet at the same point instead of separating out.
Without lenses like these built in to the design, quality
can suffer.
Aspheric elements also help to limit aberrations by refocusing
light waves at the edge of the lens to the same distance as
light waves that enter through the center of the lens. Spherical
lenses can’t do this because of their pronounced curvature,
and color aberrations can occur in your image. Lenses that
incorporate two aspheric elements will correct for the blue
and red waves, while three aspheric elements will additionally
correct for the green. When aspheric elements work in conjunction
with the other special glass elements mentioned, increased
correction for various types of aberrations are made.
Newer optics called diffractive optical (DO) elements use
a special optical construction to reduce the size and weight
of the lens while maintaining high optical quality.
Coating
Several manufacturers have included multi-coatings on their
lenses. Usually, there are seven or eight coatings layered
on the optics to help reduce reflections that cause flare.
When flare is limited, contrast and color saturation are increased
in your image. Digital SLR sensors have a shiny surface that
reflects more light than film. Because this surface increases
the chance of flare occurring, improved multi-coating becomes
essential in digital shooting.
Although each manufacturer’s coating is different and
made from various materials, you can be assured that tests
have been done to prove the reduction or elimination of flare
and ghosting.
Internal Focusing
Many lenses today have an internal focusing (IF) mechanism,
which offers great advantages. An IF mechanism moves elements
inside the lens to focus without extending the barrel of the
lens. This makes for more compact and lighter construction,
which is especially useful if you’re carrying a telephoto
on a trek. Additionally, by keeping the barrel from extending
during focusing, better balance of your camera is achieved,
whether you’re using a tripod or handholding your camera.
IF also keeps the front end of your lens from rotating so
your filters stay in place.
Lens Stabilization
If you’re shooting in a low-light situation, consider
a long zoom lens with lens stabilization. Also known as Image
Stabilizer (IS) by Canon, Vibration Reduction (VR) by Nikon
or Optical Stabilizer (OS) by Sigma, this function automatically
corrects for camera shaking that can cause blur. If you plan
on handholding a long lens, using a slow shutter speed, or
if you have a lightweight tripod that isn’t strong enough
for a heavy lens, this mechanism can equal a two- to three-stop
difference and produce a sharp image that would otherwise
turn out blurry due to unsteady support.
Size And Weight
New materials and optical innovations have allowed for smaller
and lighter lenses to be made. Lens designers are working
to continually reduce the size of their lenses and still retain
quality. Lenses specifically created for smaller-sized digital
SLR sensors are particularly compact and lightweight. So,
if you want to save your back and shoulders from the distress
that a heavy pack can cause, lighten your load. Carry less
by carrying more zooms!
Zoom
Chart PDF
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