Nov 2009 - Signpost Magazine

Getting the best from
your telephoto lens
By Ash Jamieson, Vizzisign Digital
Though telephoto lenses
are all the rage with
digital camera users,
it seems many don’t really
get the best results from their
equipment.
A few easy to apply rules can
make the difference between
good and terrific shots.
Of course the most advised
precaution when using a lens
6 Signpost Community Magazine - November 2009
with a long focal length (greater
than 100mm) is to mount the
camera on a tripod or rest it on
a firm surface when taking the
shot. Very sound advice indeed.
There is a key aspect in the
behavior of telephoto lenses
which once understood can be
adjusted quite easily with various
settings and features of the
camera itself. It is the ‘speed’ of
This galah was taken using a 300mm Canon lens fixed on a 5D Mk1 camera
the lens (telephoto lenses are
much slower than a standard
lens).
Lens speed is expressed with a
ratio number something like 1:1.4
which essentially denotes how
much light the lens will allow to
pass through it at its optimum.
The lower the second number
the greater amount of light can
pass and so the ‘faster’ the lens.
A good quality 100mm
telephoto lens will be typically
rated at 1:2.8, a 200mm at 1:4.
(Zoom lenses complicate this
somewhat as the speed of the
lens varies according to the
amount of zoom being applied at
the time – the greater the zoom
being used, the ‘slower’ the lens)
Lens speed (slower) causes
one of the most common issues
experienced; loss of depth
of field*, usually caused by
operating the camera in AUTO
or PROGRAM mode.
These modes are designed
to capture the ‘best’ image
every time by compensating for
camera movement. The camera
automatically sets the highest
possible shutter speed / aperture
combination for each shot which
usually results in a shallow depth
of field. Retaining a greater depth
of field in your images can be
accomplished in two ways:
Increase the ISO setting
of the camera – ISO400 will
still yield very good images and
enable use of a higher shutter
speed/aperture combination.
Change to MANUAL mode
and set the aperture to f8 or
higher and adjust the shutter
speed to accommodate.
* Depth of field is exhibited as
loss of focus beyond the subject and is
governed by the size of aperture used
– the lower the ‘f’ setting the shallower
the depth of field. The challenge is to
balance shutter speed and aperture
for the desired effect. Any increase in
aperture number has to be compensated
with a slower shutter. ♦