Canon Rebel T1i + EF-S 18-55mm IS 3818B0043 User Manual (en)

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stores the flash output required for optimum
exposure of the main subject (as identified by
the AF point) and the background. E-TTL requires
the use of EX-series dedicated Speedlites
such as the 580EX II, 430EX II, 270EX, 220EX,
MT-24EX, or MR-14EX in combination with a
compatible camera.
E-TTL II—Available on Canon’s EOS Digital SLR
cameras, E-TTL II incorporates distance information
from compatible EF lenses (see page 30 for
details) for more versatile flash exposure control.
E-TTL II minimizes underexposure that can occur
with straight reflections by ignoring sensor areas
that report abnormally high levels. This feature
is useful when shooting a subject with a highly
reflective object in the background, or if the
subject itself is highly reflective. In addition,
because distance information is used in calcu-
lating the flash output level, E-TTL II prevents
overexposure when photographers lock focus
and recompose.
For example, with the EOS-1D Mark IV, the ambient
light is first measured using the camera’s 63-zone
metering when the shutter button is pressed.
Next, a preflash is fired and the metering sensor
takes readings. The ambient and preflash readings
are compared. The metering areas having small
differences are selected as the main flash exposure
areas. Areas with large discrepancies between
ambient and preflash readings are excluded or
down-weighted because they are assumed to
contain a highly reflective subject, or the subject
is not in that part of the frame—an assumption
validated by distance information. The algorithm
thus helps avoid chronic underexposure problems
in such situations. These readings are weighted,
averaged, and compared with the ambient light
reading and the main flash output is then set
and stored in memory.
The E-TTL II, in effect, captures the subject as a
“plane” and not as a “point.” As a result, EOS
SLR cameras can help deliver consistent flash
exposures even if the subject contains various
colors and levels of reflection. The camera also
allows the user to select an averaged metering
pattern through custom function settings. 
TTL*TTL (Through-The-Lens) is the standard
flash exposure control mode used by the built-in
flash units that come with some 35mm EOS film
cameras. Unlike E-TTL or E-TTL II, TTL reads flash
illumination reflected from the film during the
exposure. When the camera is set to Program AE
mode, TTL flash sets an aperture based on the
ambient light level.
Flash Exposure Lock (FE Lock)
FE Lock adds Auto Exposure lock and Spot metering
functions when shooting with EX-series Speedlites
and E-TTL compatible EOS cameras. The EX-series
Speedlite’s preflash fires when the camera’s AE
Lock button is depressed, storing a Spot meter
reading of flash and ambient lighting data for up
to 16 seconds. This provides enough time to not
only recompose the shot, but also alter the ambient
light exposure for maximum creative control. FE
Lock is extremely useful when you wish to recom-
pose after focus lock or to place the main subject
in a part of the frame not covered by one of the
focusing points. It can also eliminate potential
exposure errors caused by unwanted reflections
from surfaces like windows or mirrors.
Adjusting Ambient Exposure in FE Lock**After
preflashing the subject with the FE Lock button,
ambient exposure can be adjusted by turning the
Quick Control Dial. The ambient exposure level is
displayed on the exposure level scale in the
viewfinder and on the external LCD panel. 
FP Mode***
FP (focal-plane) flash, or High-speed Sync, enables
E-TTL and E-TTL II compatible cameras equipped with
an EX-series Speedlite to synchronize flash at shut-
ter speeds faster than the camera’s normal maximum
sync speed. Even in bright daylight, for example,
a fast lens can be used at a wide aperture to reduce
depth-of-field and emphasize the subject. FP flash
can be combined with E-TTL, E-TTL II, or FE Lock,
and is available in all AE modes plus Manual.
Flash Exposure Compensation****
This setting adjusts flash output without changing
the shutter speed or aperture. It’s a particularly
effective way to fine-tune the balance between
foreground and background exposure for fill flash
shots, but it can also be used to compensate for
extremely bright or dark tones in the subject.
Second-Curtain Sync
Instead of firing the instant the shutter opens,
Second-Curtain Sync fires the flash at the end of
the exposure, allowing streaks of light to flow
naturally behind a moving subject. This creative
flash mode is most effective with slower shutter
speeds and subjects with light sources, such as
the headlights of a moving car. 
Stroboscopic Flash
Stroboscopic flash is a series of flashes fired in
rapid succession during a single exposure. With
stroboscopic flash, multiple images of a moving
subject appear in the photograph. Using this
mode, you can analyze a golf swing or record the
shattering of a windowpane. (Available with
Speedlite 580EX II, Macro Ring Lite MR-14EX
and Macro Twin Lite MT-24EX, the built-in flash
of the EOS 7D).
Integral to the EOS System, Canon Speedlites
are the ideal flash source for EOS SLR cameras.
They are technologically advanced to provide
perfect exposure and illumination with just
about any subject, yet operation is remark-
ably simple. Whether you’re an amateur or
an expert, Canon Speedlites make it easy to
obtain professional results.
41
Sophisticated Flash Control Modes
E-TTL—In E-TTL (Evaluative Through-The-Lens) flash
exposure control mode, meter readings are taken
through the lens, but not off the focal plane. Using
a preflash fired after the shutter button has been
fully depressed—but before the camera’s reflex
mirror goes up—E-TTL uses the camera’s Evaluative
metering sensor to compare the ambient light
values with the light reflected from the subject
by the preflash. The camera then calculates and
SLR Compatibility
Speedlite Compatibility
† Not Linked to AF point.  †† Requires EOS body that supports E-TTL and E-TTL II respectively.  ††† Defaults to TTL in all conditions
except direct flash in the camera’s Program mode.
High-Speed Sync — EF 135mm f/2.0L USM lens •f/2 •1/750 sec.
Taken with MT-24EX and EOS-1v HS
*ATTL and TTL are not compatible with digital SLR cameras. See lens chart for a listing of lenses that supply distance information. **Ambient exposure cannot be adjusted when the camera is set to Bulb mode or in
low-light situations when the camera is set to Program AE or A-DEP. ***Unlike conventional electronic flash, FP flash output (guide number) decreases as shutter speed increases above normal X-sync speed. ****Flash
exposure compensation can be set with most current Speedlites, and it can also be set with all current EOS cameras other than the EOS Rebel series and EOS Digital Rebel. 
580EX II
430EX II
270EX
220EX
MR-14EX
MT-24EX
Camera Model
EOS-1Ds Mark III
EOS-1D Mark IV
EOS 5D Mark II
EOS 7D
EOS 50D
EOS 40D
EOS 30D
EOS Rebel T2i / T1i / XSi / XS
EOS Digital Rebel XTi / XT
EOS-1v / EOS-3
EOS ELAN 7
NE
EOS Rebel T2 / T2 Date
EOS Rebel K2 / K2 Date
E-TTL / E-TTL II
Yes
††
Yes
††
Yes
††
Yes
††
Yes
††
Yes
††
A-TTL
No
No
No
No
No
No
TTL
Yes
†††
No
No
Yes
†††
Yes
†††
Yes
†††
Manual
Yes
Yes
No
No
Yes
Yes
E-TTL II
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
E-TTL
No
No
No
No
No
No
No
No
No
Yes
Yes
No
Yes
A-TTL / TTL
Not Possible
Not Possible
Not Possible
Not Possible
Not Possible
Not Possible
Not Possible
Not Possible
Not Possible
4-point / 3-zone
4-point / 3-zone
Not Possible
4-point / 3-zone
SPEEDLITES
SPEEDLITE TECHNOLOGY