Specifications

III. NEW AND IMPROVED DESIGN FEATURES 12
New E-TTL II Autoflash
Algorithm
New Built-In Flash
As
with the EOS 10D, AF-assist is provided by a series of strobo-
s
copic flashes from the built-in flash or an external, EOS-dedicated
S
peedlite. The working range for the built-in AF-assist function is approxi-
m
ately 4m/13.1 ft. at the center and approximately 3.5m/11.5 ft. at the
other 8 AF
points. Custom function 5 enables and disables this
f
eature. Optional Speedlite 580EX is equipped with a powerful
AF
Assist beam that is effective at distances up to 10m/33 ft.
when greater distance is desired.
The new E-TTL II autoflash control uses the algorithm just introduced in
Canon’s professional landmark EOS-1D Mark II. E-TTL II takes effect when the built-in flash
or an EX-series Speedlite is used. It is no longer assumed that the AF point covers the main
subject. Now, when the shutter button is pressed completely, ambient light is measured just
before a pre-flash fires. For each metering zone, the ambient reading and the pre-flash read-
ing are compared.
Areas having a large difference between ambient and pre-flash readings are selected.
Extreme differences suggest a highly reflective or specular object; these areas are
eliminated from calculations, avoiding underexposure. When a lens providing distance
information is used, this data is also considered in determining the presence and
location of a high-reflectance object. The selected pre-flash readings are added and
averaged and the output of the main flash is calculated. Even if the subject changes
position, reflectance or size, the flash metering remains highly accurate and stable.
The new, built-in flash of the Canon EOS 20D supports E-TTL II and has an arm that permits
the flash center to be 18.6mm higher than the unit on the EOS 10D. This reduces the
chance that red-eye will occur or that the lens barrel will obstruct flash coverage. The
relative positions of the reflector and the xenon flash tube have been optimized and the
fresnel flash panel’s transparency has been increased, permitting a wider field of coverage,
up to a 17mm focal length (equivalent to 27mm in 35mm format), while maintaining
the s
ame guide number as the EOS 10D’s flash unit.
The built-in flash and the new accessory Canon 580EX
Speedlite send color temperature data to the processor each
time the flash fires. This useful feature takes into account
a host of variables, including battery condi-
tion and flash duration, offering assur-
ance of unprecedented color accuracy
and consistency from shot to shot.
The built-in flash’s retraction and pop-up
have been improved with rubber fitted to
the stopper in order to cushion the pop-
S
peedlite 580EX on EOS 20D