Canon EF 35-80mm f/4-5.6 III Lenses Manual Download Page 11

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Image Stabilizer

No matter how great the lens is,
camera shake can spoil the shot.
Blurred photos due to camera shake
usually occur when the shutter
speed is slower than the reciprocal
of the lens focal length.
For example, a shutter speed slower
than 1/200 sec. at the 200mm focal
length can invite a blurred photo
caused by camera shake. In such
cases, a tripod is necessary.
However, a tripod can be a heavy
and troublesome burden when you
go hiking or travelling. There are
even places where using tripods is
prohibited. Using a slow shutter
speed then becomes difficult.
To resolve this problem, Canon
became the first manufacturer to
incorporate an Image Stabilizer in an
SLR camera lens. Optical shake is
detected by gyro sensors which
provide the data necessary to shift
the image-stabilizing lens group in
parallel to neutralise the shake.
This increases the usable shutter
speed range by up to two full steps
for hand-held shooting. Except for
the EF 28-135mm f/3.5-5.6 IS USM
and EF 75-300mm f/4-5.6 IS USM
lenses, IS lenses have two IS modes.
One is for normal image stabilisation
and the other is for panned shots.
With a monopod, the Image
Stabilizer on all IS lenses operates
normally as during hand-held
shooting. Also, the EF 300mm f/2.8L
IS USM, EF 400mm f/2.8L IS USM,
EF 500mm f/4L IS USM, and EF
600mm f/4L IS USM lenses have a
mechanism that prevents having the
Image Stabilizer turned on while the
lens is mounted on a tripod.

Floating System

Ordinary lenses are designed to
give the best results when the
correction of aberrations is most
effective. This is usually at the most
commonly used focusing distances.
At other focusing distances,
especially at the closest focusing
distance, aberrations tend to appear.
Canon’s floating system suppresses
aberrations at close focusing
distances. This system adjusts the
gap between certain lens elements
in correspondence to the focusing
distance. The aberration is effectively
corrected. The result is high image
quality with aberrations suppressed
at all focusing distances.

Circular Aperture

Certain Canon lenses feature a new
Circular Aperture diaphragm unit,
which uses curved aperture blades
to provide for a more rounded
opening as the lens is stopped down.
It’s especially effective at rendering
out-of-focus background highlights
as natural rounded shapes. In lenses
such as the EF 70-200mm f/2.8L IS
lens, the lens opening is virtually
circular from f/2.8 to f/5.6.
These lenses retain all the benefits
previously available with Canon’s
Electromagnetic Diaphragm
— smooth and consistent stop-down
operation (even at up to 10 fps
with the EOS-1v), near-silent aperture
control, and total absence of
mechanical levers or switches in
the lens mount.

Full-Time
Manual
Focusing

Canon EF lenses and EOS cameras
have very high AF precision.
Optimum focus can be achieved
quickly for almost any shooting
situation. Recent EOS cameras have
been equipped with multiple
focusing points for higher flexibility
in composing a photo while using
AF. Picture-taking is even more
flexible with Canon’s full-time manual
focusing which overrides the
autofocusing mode. Lenses with
this feature allow you to switch to
manual focusing even in the AF
mode. You can keep looking through
the viewfinder and touch up the
focus manually without switching
the focus mode switch. Since the
focusing ring does not rotate during
autofocusing, we could make it
wider for better holding comfort and
easier manual focusing. Another
ergonomic design which lets you
convey your intentions quickly.
Full-time manual focusing comes in
two types. One is electronic manual
focusing where the rotation amount
of the focusing ring is detected and
the focusing motor is driven
electronically. The other type is
mechanical manual focusing where
the rotation of the focusing ring
adjusts the focus mechanically.

AF Stop Feature

AF stop is featured on the EF
300mm f/2.8L IS USM, EF 400mm
f/2.8L IS USM, EF 500mm f/4L IS
USM, and EF 600mm f/4L IS USM
lenses. If something passes between
the camera and subject during
autofocusing, pressing the AF stop
buttons momentarily locks the AF
to prevent the focus from shifting
to the obstruction passing by.
After the obstruction is gone,
the focus is still maintained on the
subject and you can quickly resume
shooting. The AF stop buttons are
positioned at four locations around
the lens grip at the front of the lens
for easy access during both
horizontal and vertical shooting.

Dust- and Water-Resistant
Construction

The new EF 300mm f/2.8L IS
USM, EF 400mm f/2.8L IS USM,
EF 500mm f/4L IS USM, and
EF 600mm f/4L IS USM lenses are
highly dust- and water-resistant.
The switch panel, exterior seams,
and drop-in filter compartment have
rubber linings. Moving parts such
as the focusing ring and switches
are also designed to prevent water
and dust from entering. These lenses
can therefore be used in harsh
conditions without dust and water
getting inside.

The lens is equipped with a rubber
ring on the mount to improve its
dustproofing and waterproofing
characteristics. As the lens is
repeatedly mounted and detached,
the rubber ring will leave fine
abrasion marks on the outside
of the camera mount. This will not
affect operation.

Technology where it counts

Canon’s innovations put your images on film quickly, quietly, and easily with outstanding results.

Ultrasonic Motors (USM)

The Ultrasonic Motor (USM) in
Canon EF lenses is the world’s
first lens-based motor. Based on
a totally new technology, the motor
spins by ultrasonic oscillation energy.
The USM is quiet and quick. It has
made EF lenses almost noiseless
and autofocusing fast, precise,
and practical. The direct-drive
construction is very simple, with no
gear train. This makes it durable and
efficient. It also consumes little power.
Two types of USM are used:
Ring-type USM and Micro USM.
The former type is found in
large-aperture and super telephoto
lenses, while the latter is used in
more compact lenses. Using the
optimum type of USM in the
lens results in maximum efficiency
and effectiveness.

Aspherical Lenses

Ordinary spherical elements have
an inherent flaw in that the
point of focus for the lens centre
does not match that of the lens
periphery. Spherical aberrations of
large-aperture lenses and distortion
by ultra-wide-angle lenses cannot
be resolved with spherical elements
alone. The Aspherical lens element
was therefore developed.
The curvature of the lens element is
calculated and shaped to achieve the
ideal single point of focus. The result
is high contrast with minimal flare
even with a large-aperture lens.
Distortion can also be effectively
corrected in ultra-wide-angle lenses.

Canon started to develop
manufacturing technology for
Aspherical elements early on.
We eventually succeeded in
establishing a mass-production
grinding and polishing process with
a polishing precision of 5/10,000 mm.
In 1971, Canon marketed the
FD 55mm f/1.2AL lens, the world’s
first large-aperture Aspherical lens
for SLRs. This was followed by many
other Canon lenses incorporating
Aspherical elements and they were
well-received.

Also, Canon developed
mass-production technology for
glass-moulded aspherical elements
and replicated Aspherical lenses.
The former was produced by an
ultra-high-precision aspherical
lens-moulding machine which
shaped the glass directly. For the
latter, the Aspherical surface was
formed by ultraviolet-hardened resin
film applied on a spherical element.
Canon has developed numerous
compact-size lenses, taking full
advantage of Aspherical elements
to attain high image quality.

Diffractive Optics

In another world’s first in camera
lens optical design, Canon introduced
new technology in order to build a
super telephoto that complements its
latest compact film and digital SLR
cameras. This cutting-edge technology
employs diffractive optical elements
that use the principle of diffraction
to change the direction of the
lightwave’s path. This revolutionary
element has Aspherical
characteristics, which help define
superior maximum aperture image
quality, as well as optical qualities
superior to UD-glass to totally
correct colour fringing.
The Multi-Layer Diffractive Optical

Elements exhibit outstanding ability
to correct chromatic aberrations
(colour defects), and are especially
effective in super telephoto lens
design where these specific types
of optical defects are most likely to
happen. You can see how well the
technology works in your own
pictures by examining the straight
edges of a subject in your picture.
You will see a crisp, clear edge
without the telltale, prismatic colour
fringing that is visible with images
shot using inferior optics.

Glass lens elements refract, or bend,
lightwaves as they pass through to
form an image. That’s simply the
naturally occurring physics of light.
We use multiple elements and
special glass to help keep the waves
focused like a pinpoint instead of
spreading them into the rainbow of
colour seen when light passes
through a glass prism. To diffract a
lightwave means that the ray goes
through a change in direction before
passing through the lens. The change
in direction is caused by a diffraction
grating – very fine parallel grooves
or slits on the surface. Canon found
that using a concentric diffraction
grating that gets smaller toward the
edges – some as fine as tenths of a
micrometre – solved of one many
inherent physical limitations of
camera optics. The design also
makes it possible to obtain the
same effect as an Aspherical lens.
And taking the technology a step
beyond, we actually use two
single-layer diffractive optical
elements whose diffraction gratings
are bonded together face-to-face.

Since longer wavelengths form an
image closer to the lens due to the
large diffractive angle, and shorter
wavelengths form an image farther
from the lens due to the smaller
diffractive angle, putting the DO
elements with conventional glass
optics actually cancels out each
other’s chromatic aberrations and is
exceptionally effective in correcting
this optical defect. The diffraction that
occurs with Canon’s Multi-Layer
Diffractive optical elements actually
corrects the optical system’s
chromatic aberrations and improves
the image formation performance.

The net result of Canon’s
DO technology is a lens design
with reduced size and weight while
offering higher image quality than a
comparable focal length lens that
incorporates conventional glass
optical elements. It means a new
generation of high-performance
lenses that complement the more
compact designs of our latest
SLR film and digital cameras.

MRing-type USM

Micro USM

Spherical aberration of spherical lens.

Convergence of parallel light rays by
an Aspherical lens.

Refractive Optical Element

Chromatic aberration
canceled out

Refractive Optical
Element and Multi-
Layer Diffractive
Optical Element
Combined

Chromatic aberrations
reversed from that of a
refractive optical element

Image formation in the red, green,
and blue wavelength order

Red

Green

Blue

Multi-Layer Diffractive
Optical Element

Image formation in
the blue, green, and
red wavelength order

Chromatic aberrations

Diffractive
grating

Glass
lenses

Cross-section

Front view

Correction of Chromatic Aberration by the
Multi-Layer Diffractive Optical Element

Multi-Layer Diffractive Optical Element Construction

400mm f/4 Lens Designed with a Refractive
Optical Element Only

400mm f/4 DO IS USM

(Incorporates Multi-Layer Diffractive Optical Element)

UD element

317mm

Weight: 3,000g

Fluorite

Multi-layer diffractive optical element

232.7mm

Weight: 2,080g

(Including removable

tripod collar)

Fluorite

Lens Downsizing with the Multi-Layer Diffractive
Optical Element

Note: If a very bright spotlight like a mercury lamp
is photographed with a DO lens, a ring of light
may occasionally appear around the light source,
due to the imaging characteristics of the Multi-
Layer Diffractive Optical Element.

1: No camera shake

2: Lens front shakes downward

3: Image-stabilizing group counteracting
downward camera shake

Group 1 (focusing group)

Group 2 (image-stabilizing group)

To
Object

Group 3 to 6

Film
plane

Direction of Group 2
movement

How the Image Stabilizer Works in the
EF 75-300mm f/4-5.6 IS USM

With Image
Stabilizer on

With Image
Stabilizer off