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LENSES
Sensor Crop Factors
The actual focal lengths of kit lenses
varies with the sensor format of the camera
they’re designed for. But the typical range
is equivalent to about 28-75mm in
35mm format.
Different sensor sizes apply different
‘crop factors’, which inÁuence the Àeldof-view coverage of the lens. Crop factors
relate the effects of smaller sensors to the
traditional 35mm Àlm format. The table
below compares the kit lenses in the main
camera formats.
Crop factors inÁuence the depth of Àeld
of lenses. The larger the sensor, the more
control the photographer has over the plane
of sharpness in an image. And the narrower
the plane of focus, the greater the ability to
blur background details.
Examples of the zoom range of a typical kit lens.
(Taken with the Olympus M.Zuiko 14-42mm
F3.5-5.6 II lens at 14mm and 42mm.)
Few kit lenses are long enough to take closeups of animals and birds in the wild, although
they are Àne for photographing pets. .it lenses
are also unsuitable for close-up shots of sports
action. For some subjects, simply moving closer
could solve the problem.
Photographers who enjoy shooting extreme
close-ups will also Ànd a kit lens limiting.
A dedicated macro lens will probably be
required, or a telephoto zoom with good
close-focusing capabilities.
5. Flare. .it lenses are often Áare-prone.
This can often be solved by Àtting a lens hood.
Unfortunately, few manufacturers supply
hoods with their lower-priced lenses so you
should consider adding a hood when the kit
lens is purchased.
Kit lenses are often sold without lens hoods, which
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illustration.
48
PHOTOREVIEW AUSTRALIA | Issue 56
Depth of Àeld of a lens increases as the
size of the camera’s sensor is reduced.
That’s why it’s so easy to take sharp
pictures with compact digicams (or cameraphones) but so difÀcult to isolate subjects
from distracting backgrounds.
The sensor’s crop factor can give you
some idea of how much greater the
inherent depth of Àeld is for smaller sensor
formats, compared with a standard 35mm
camera. For example, a lens with an f/1.8
aperture will have a wider depth of Àeld on
the small Micro Four Thirds sensor than a
f/1.8 lens on an APS-C camera, which will
itself be larger than a f/1.8 lens with a
full frame sensor. This is something to be
aware of if you want smooth out-of-focus
backgrounds in shots.
Sensor format/
size
Crop factor
Main focal
length range
35mm
equivalent
Common
alternatives
‘FX’ / 36 x
24 mm
1x
24-70mm
24-70mm
24-85mm,
24-105mm
‘DX’ / a23 x 15
mm
1.5x / 1.6x
18-55mm
27-82.5mm
18-70mm,
17-85mm
M4/3 / 17.3 x
13.0 mm
2x
14-42mm
28-84mm
14-45mm
‘CX’ / 13.2 x
8.8 mm
2.73x
10-30mm
27-81mm
11-27.5mm
Pentax Q / 6.17
x 4.55 mm
5.83x
5-15mm
27.5-83mm
n.a.
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background that would isolate the subject.
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