Datasheet
Glossary
M
MICRO MOTOR
A tiny motor which replaced the
use of AFD autofocus motors.
MICRO USM
A type of Ultrasonic Motor (USM)
that is used in some EF lenses.
Micro USM motors allow faster AF
performance than the standard
micro motor found in some
EF lenses.
R
REAR FOCUSING
A method of internal focusing in
which only the lens elements closest
to the rear of the lens are moved.
Allows for faster and smoother
focusing.
RESOLUTION
A measure of a lens’ ability to
discern detail.
RING–TYPE USM
A type of Ultrasonic Motor (USM)
found in most EF lenses. One of the
key advantages of the ring–type USM
is that it allows for full–time manual
focus in AF mode. This means that
focusing can be fine–tuned manually
after autofocusing has finished,
without having to switch to manual
focusing mode.
S
SPHERICAL ABERRATION
An optical phenomenon whereby
light rays entering at the edges of
spherical lens elements converge at
slightly different focal points to light
rays entering from the centre. This
produces soft, low contrast images
that look as if covered with a thin
veil. Aspherical lenses are used to
counteract this problem.
SUBWAVELENGTH STRUCTURE
COATING (SWC)
A new anti-reflective coating that
mimics the surface of moths’ eyes
and effectively eliminates ghosting
and flare. Subwavelength structure
coating consists of tiny structures
on the surface of the lens that are
smaller than the wavelength of
light and prevent reflections
from occurring.
SUPER SPECTRA COATING
A multilayer anti–reflective coating
developed by Canon to minimise
ghosting and flare.
SUPER UD GLASS
Super UD is an improved version
of Ultra–low Dispersion (UD) glass,
exhibiting a lower dispersion of light.
Used in many professional
L–series lenses.
T
TELEPHOTO
A lens that brings distant subjects up
close. Typically, any lens with a focal
length above 50mm.
U
ULTRA–LOW DISPERSION
(UD) GLASS
An optical material that exhibits
low dispersion of light, developed
by Canon to minimise chromatic
aberration.
ULTRASONIC MOTOR (USM)
A lens–based technology which
drives fast, accurate and virtually
silent auto focus. Canon provides
two types of USM – ring–type
USM and micro USM.
V
VIGNETTING
A fall–off in brightness at the edges
of an image causing the corners of
an image to appear dark. Wide–angle
lenses are more likely to suffer
from vignetting.
W
WIDE–ANGLE
A lens that has a shorter focal length
and wider field of view than a
standard 50mm lens.
WORKING DISTANCE
The distance from the front of the
lens to the subject, an important
factor in macro photography.
A longer focal length will give
a greater working distance.
FOCUS MODE AND FOCUSING
RANGE SWITCHES
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