Canon EOS Rebel T2i Brochure page 17

Floating System Dust- and Water-Resistant
Construction
Typical lenses correct for optical aberrations
only at commonly used focusing distances. Not Most L-Series EF
surprisingly, at other focusing distances, especially telephoto lenses are
close range, aberrations can compromise image highly dust- and
water-resistant thanks
TS-E 24mm f/3.5L Floating System
to rubber seals at the
Focal plane
switch panels, exterior
Closest
shooting
seams, drop-in filter
distance
compartments and
Floating
lens mounts. Moving
parts, such as the focusing ring and switches,
are also designed to help keep out environmental
contaminants, providing reliable performance
under harsh conditions.
Floating Effect
(TS-E 24mm f/3.5L)
TS-E Movements
Tilt Movements alter the angle of the plane of focus between the lens and focal plane, and Shift Movements move the lens's
optical axis in parallel.
Astigmatism
quality. Rather than using fixed spacings, Canon's
floating system dynamically varies the gap
between key lens elements based on focusing
distance. Most aberrations are effectively sup-
pressed throughout the focusing range, assuring
high image quality in all shooting situations.
Circular Aperture
Canon lenses featuring circular aperture diaphragms
Reverse tilt and shift greatly reduces the range on which focusing
employ curved blades to create a smoothly rounded
is possible.
opening as the lens is stopped down. As a result,
most out-of-focus background highlights are
rendered as natural-looking rounded shapes
rather than as distracting polygons. These lenses
deliver smooth, consistent stop-down action
(even at 10 fps), near-silent operation and
excellent optical characteristics.
Inner and Rear Focusing
An inner focusing lens has the focusing lens
The lens's tilt mechanism is used to achieve a pan focus effect
group(s) in front of the diaphragm, while a rear
that allows focusing all the way back.
focusing lens has the focusing lens group(s) behind
Tilt Movements –Using a normal lens, shallow or deep focus is
the diaphragm. Both designs allow for compact
controlled by the size of the aperture used to adjust depth-of-
optical systems that produce faster AF. And because
field. Canon TS-E lenses can help achieve this by the tilting of
the front of the lens does not rotate to focus, filter the lens barrel in relationship to the focal and subject planes.
This allows for the appearance of extremely deep focus even at
orientation remains constant.
wide open apertures, and shallow focus at smaller apertures.
AF Stop Feature
Pressing the AF Stop button (featured on several
EF IS telephoto lenses) momentarily locks the AF
to help prevent the focus from shifting to a passing
obstruction. After the obstruction has cleared, the
focus will still be on the subject, and you can quickly
resume shooting. AF Stop buttons are positioned at
Using Tilt Movements to Focus an Oblique Subject Plane
four locations around the lens grip for easy access.
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EF 24mm f/1.4L II USM •f/2.8 •1/30 sec.
Full-Time Manual Focusing
Canon EOS cameras with EF lenses deliver impec-
cable AF precision. Manual focusing capability,
nevertheless, can enhance flexibility. Canon EF
lenses with full-time manual focusing enable the
photographer to manually tweak focus without
switching out of AF mode. Since AF action does
not cause the focusing ring to turn, it can be made
wider for improved grip and comfort.
Shift was used to adjust the image to keep the building
perpendicular all the way to the top.
Without using shift causes the image of the building to lean in at
the top.
Shift Movements – By keeping the camera level, and
using the shift function to raise the lens instead, this per-
spective effect can be corrected. With the camera's focal
plane set parallel to the building, shifting the lens upward
will obtain a more rectangular-looking building.
Depth-of-field with tilt movements
Plane of optimum focus
Film plane
With a normal lens
Using Shift Movements to Focus Tall Building
–
EF 8 15mm f/4 Fisheye •f/4 •1024 sec.
–
EF 8 15mm f/4 Fisheye •f/5.6 •1/200 sec.
Specialty Lenses
Fisheye — With its unique focal length range,
the EF 8-15mm f/4L Fisheye USM is the world's
widest fisheye zoom lens. It delivers 180°
diagonal angle of view images for all EOS SLR
The diagram below shows the relationship between each
image size and a 180˚ angle of view for each focal length.
Focal Length: 8 mm Approx. 10 mm
Full size
Circular fisheye Full-frame fisheye
Approx. 12 mm Approx. 15 mm
APS-H
Full-frame fisheye Full-frame fisheye
*The red circle for each forcal length is the size of a 180˚ angle of
view on the image plane.
cameras with imaging formats ranging from full-
frame to APS-C, and provides 180° circular fisheye
images for full-frame EOS models. This new Canon
lens has a wide zoom range feature that provides
a truly elevated level of creativity and performance
for users shooting artistic compositions or
FOCAL LENGTH COMPARISON
15mm Fisheye 14mm
180° 114°
With a TS-E lens
85mm 100mm
28° 30' 24°
panoramic landscapes, as well as astronomy
and sports.
EF-S Lenses — Designed for the Canon EOS 7D,
EOS 60D and all EOS Rebel models with APS-C
sized sensors (with a 1.6x crop factor), Canon's
EF-S lenses take advantage of the sensor's smaller
size to help deliver optimized performance in
compact, lightweight designs. The EF-S 15–85mm
f/3.5-5.6 IS USM is a perfect example of this
technology. With a compact design, a 35mm
equivalent range of 24–136mm, and Optical
Image Stabilizer technology, it's a superlative
walk-around lens... possibly the only lens you'll
need to enjoy basic Canon digital SLR photography.
TS-E — TS-E lenses are capable of tilt and shift
movements, which bring many of the advantages
of technical view cameras to the EOS System. Tilt
movements alter the angle of the plane of focus
between the lens and film plane, making broad
depth-of-field possible even at larger apertures;
shift movements slide the lens's optical axis along
the film/sensor plane, enabling photographers
to correct or alter perspective at almost any angle.
Macro — Canon's EF lens lineup has a number of
options for true close-up and macro photography.
APS-C
With five macro lenses for precision, and three
screw-on close-up lenses for convenience—in
addition to Life-Size Converter EF and two Extension
Tubes—Canon's macro lenses and close-up
accessories can uncover detail that is nearly
impossible for the unaided human eye to detect.
Full size
EF Mount
In designing the EF lens mount, Canon engineers
gave photographers a lot more than a way to quick-
ly attach a lens to a camera body. As the commu-
nication conduit between camera and lens, this
fully electronic mount system has none of the
shock, operational noise, abrasion, play, lubrica-
tion requirements, slow response, lever operation
17mm 20mm 24mm 28mm
104° 94° 84°
135mm 200mm 300mm 400mm
18° 12° 8° 15'
EF LENSES
limitations, or other design restrictions related
to mechanical linkage mechanisms. A self-test
system, using the lens's built-in microcomputer, can
even warn of malfunctions through the camera's
display. The EF mount makes possible high-speed
autofocus, precise aperture control and preview,
automatic compensation with lens extenders, and
both forward and backward compatibility with
new lens technologies—such as USM and IS—as
they are developed by Canon.
About Macro Magnification
A life-size macro lens—that is, a
1x magnification—records an
image on film at its actual size. If
you're photographing fruits, for
example, and it has a diameter of
1 in., it will occupy 1 in. of your
actual slide or negative. With a
digital SLR, at 1.0x magnifica- 0.25x
tion, the image projected onto
your camera's sensor will like-
wise be the same size at the sen-
sor plane as the actual subject
itself. Other macro lenses have
lower or higher magnifications.
A lens with 0.5x magnification
will produce an image on film
0.5x
that is half the size of the
actual subject. Your 1 in. fruit
then would only occupy 0.5 in.
on film.
In the other direction, a 5x
magnification lens will convert
the 1-in. fruit to a 5-in. diameter
1.0x
image. Since the entire image
won't fit in the frame of your
film, you will have an enlarged
image of a detail of the fruit.
Magnification is not the same as
focal length. A 50mm lens and a
180mm might both be macro
lenses with, for example, 1.0x
3.0x
magnification. The advantage of
the longer lens is that it allows
greater distance from a subject,
while allowing the same magnifi-
cation in the final image. The
180mm lens is ideal for shooting
tiny subjects without disturbing
them; the 50mm is better choice
5.0x
for copying flat documents.
35mm 50mm 70mm
75° 63° 46° 34°
500mm 600mm 1200mm
6° 10' 5° 4° 10' 2° 5'
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