A
ANGLE OF VIEW
The area of a scene that can be
covered by the lens, measured
in degrees. The angle of view is
determined by the focal length
of the lens. Smaller focal lengths
give a wider angle of view.
APERTURE
The adjustable lens opening through
which light passes to the image
sensor or film. Aperture size is
indicated by an F-stop – the
higher the value, the smaller
the lens opening.
ARC FORM DRIVE (AFD)
Used by some older EF lenses
the AFD motor drives the lenses
autofocus system. An arc form drive
is basically a conventional small
motor unit, but shaped to fit inside
the curved barrel of a lens.
ASPHERICAL LENS
An element used to counteract the
problem of spherical aberration.
A special non–spherical surface
converges central and peripheral
light rays at a single focal point to
help maintain uniform sharpness
over the whole image area.
B
BOKEH
Refers to the way in which out-of-
focus points of light are rendered in
an image. Derived from the Japanese
word ‘boke’, meaning ‘fuzzy’. Blur
that comprises of smooth, uniformly
circular points of light is considered
good bokeh.
C
CHROMATIC ABERRATION
An optical phenomenon caused by
different wavelengths of light bending
at different angles when passing
through the lens, resulting in
colour distortion.
CONTRAST
The range of difference between the
light and dark areas of an image.
CROP FACTOR
The APS–C sensor on EOS models
such as the 1000D, 500D, 550D,
50D and 7D is smaller than a
standard 36x24 millimetre frame.
The smaller sensor size has the effect
of cropping the available image area
of a standard EF lens, resulting in a
1.6x magnification of the lens’ focal
length. This extra reach is a welcome
benefit for telephoto shooting but
limits the potential of wide–angle
lenses. EF–S lenses were specifically
developed to give owners of these
cameras more wide–angle options.
D
DEPTH-OF-FIELD
The zone of sharpness in front of
and behind the subject on which
the lens is focused. Determined
by aperture size, focal length and
focusing distance.
DIAPHRAGM
Another word for Aperture, an
adjustable opening in the lens that
allows the photographer to control
the amount of light that hits the
image sensor or film frame. A greater
number of diaphragm blades makes
the aperture more circular and creates
more pleasing bokeh.
DISPERSION
The property of optical materials
that causes light refraction to vary at
different wavelengths, resulting in
chromatic aberration.
DISTORTION
An optical aberration where straight
lines in a scene are not rendered
straight in the image. Barrel distortion
is where lines bow outwards.
Pincushion distortion is where
lines bow inwards towards the
centre of an image.
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F
FLARE
Lens flare occurs when light from a
bright source enters the lens at an
angle and reflects off the internal
elements in the lens. It is typically
characterised by sunspots and
areas of low contrast.
FLUORITE
A material which exhibits extremely
low dispersion of light, dramatically
reducing the problem of chromatic
aberration. Canon pioneered the use
of artificial crystal fluorite elements
in photographic lenses.
FOCAL LENGTH
Distance between the image sensor
(or film) and the optical centre of the
lens when focused to infinity.
F–STOP
A number that represents the relative
size of the lens opening, or aperture.
The lower the f–stop, the wider
the aperture.
FLOURINE COATING
A water repellent anti static coating
applied to the front and rear elements
of a lens, ensuring easier cleaning.
G
GHOSTING
Secondary images caused by light
reflecting off elements within the
lens. Canon lens coatings effectively
eliminate the problem of ghosting.
H
HYBRID IS
Hybrid IS technology compensates
for the two different types of camera
shake (angular and shift) which
both can occur during macro and
close-up photography.
The Hybrid IS system incorporates
two sensors – one for angular
velocity that detects the extent of
angular camera shake as well as an
acceleration sensor that determines
the amount of shift-based camera
shake. Hybrid IS provides a significant
benefit over conventional Image
Stabilizer technology during
Macro photography.
I
IMAGE STABILIZER (IS)
A lens–based technology developed
by Canon to detect and compensate
for camera shake. Allowing
photographers to shoot using
shutter speeds up to five stops
slower than would normally be
possible, IS significantly increases
the potential for lowlight and
handheld shooting.
INTERNAL FOCUSING
A system whereby only the internal
lens group shifts during focusing
with no change in the physical
length of the lens. An added
benefit is that the front of the lens
does not rotate, maintaining the
effect of any attached filter.
L
L SERIES
The red ring around an L-series
lens indicates the lens features
the highest standard in optics
and performance. Providing
professional photographers with
resolution and ruggedness they can
rely on, day in day out. The lenses
contain advanced technologies to
ensure the Canon L-series lenses
are the pinnacle of the lens range.
LENS DISTANCE INFORMATION
Data regarding the distance
from the lens to the subject.
This information is measured
within the lens and passed back
to the camera, where it is used
by the E–TTL II flash algorithm
when calculating the correct flash
exposure for a scene. Most EF
lenses are capable of providing
lens distance information.
CONTROLS AND FEATURES OF AN EF LENS
Hood mount
Focusing ring Distance
scale
Focus mode
switch
Zoom ring
Lens mount
index
CANON EF LENS MOUNT
The electronic contacts (gold–plated)
of an EF mounted lens
Glossary
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