<s>
Canon	O
's	O
EOS	B-Algorithm
flash	O
system	O
refers	O
to	O
the	O
photographic	O
flash	O
mechanism	O
used	O
on	O
Canon	O
's	O
film	O
(	O
35mm	O
and	O
APS	O
)	O
or	O
digital	B-Device
EOS	B-Algorithm
single-lens	B-Algorithm
reflex	I-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
The	O
main	O
light-metering	O
technologies	O
are	O
known	O
as	O
A-TTL	B-Algorithm
,	O
E-TTL	O
,	O
and	O
E-TTL	O
II	O
.	O
</s>
<s>
The	O
EOS	B-Algorithm
flash	O
system	O
is	O
capable	O
of	O
wireless	O
multiple	O
flash	O
control	O
,	O
whereby	O
a	O
master	O
flash	O
unit	O
IR	O
(	O
ST-E2	O
)	O
or	O
RF	O
(	O
ST-E3-RT	O
)	O
transmitter	O
mounted	O
on	O
the	O
camera	O
body	O
can	O
control	O
up	O
to	O
3	O
(	O
optical	O
)	O
or	O
5	O
(	O
radio	O
)	O
groups	O
of	O
flash	O
units	O
.	O
</s>
<s>
The	O
Canon	B-Algorithm
EOS	I-Algorithm
7D	I-Algorithm
is	O
the	O
first	O
Canon	O
body	O
to	O
be	O
able	O
to	O
control	O
Speedlites	O
wirelessly	O
without	O
the	O
use	O
of	O
a	O
Master	O
Speedlite	O
or	O
IR	O
transmitter	O
;	O
four	O
other	O
EOS	B-Algorithm
models	O
,	O
the	O
60D	B-Algorithm
,	O
600D	B-Algorithm
,	O
650D	B-Algorithm
,	O
70D	B-Algorithm
,	O
and	O
700D	B-Algorithm
,	O
also	O
have	O
wireless	O
flash	O
capabilities	O
.	O
</s>
<s>
Canon	O
has	O
introduced	O
several	O
different	O
metering	O
systems	O
for	O
its	O
flash	O
products	O
:	O
A-TTL	B-Algorithm
,	O
E-TTL	O
,	O
and	O
E-TTL	O
II	O
.	O
</s>
<s>
Advanced-Through	O
The	O
Lens	O
(	O
A-TTL	B-Algorithm
)	O
is	O
a	O
through-the-lens	O
(	O
TTL	O
)	O
metering	O
system	O
that	O
was	O
expanded	O
to	O
support	O
flashes	O
.	O
</s>
<s>
A-TTL	B-Algorithm
,	O
first	O
seen	O
on	O
the	O
T90	O
(	O
which	O
predates	O
the	O
EOS	B-Algorithm
family	O
)	O
,	O
is	O
a	O
flash	O
exposure	O
system	O
that	O
adds	O
a	O
brief	O
preflash	O
during	O
exposure	O
metering	O
when	O
the	O
camera	O
is	O
in	O
the	O
programmed	O
exposure	O
(	O
P	O
)	O
mode	O
.	O
</s>
<s>
In	O
an	O
A-TTL	B-Algorithm
system	O
the	O
sensor	O
that	O
reads	O
the	O
preflash	O
return	O
is	O
located	O
on	O
the	O
flash	O
unit	O
;	O
this	O
caused	O
some	O
issues	O
especially	O
when	O
using	O
filters	O
as	O
the	O
filter	O
would	O
cover	O
the	O
lens	O
(	O
but	O
not	O
the	O
sensor	O
outside	O
the	O
lens	O
)	O
thus	O
causing	O
inaccurate	O
settings	O
.	O
</s>
<s>
Some	O
early	O
Canon	B-Algorithm
EOS	I-Algorithm
cameras	O
also	O
used	O
the	O
A-TTL	B-Algorithm
preflash	O
in	O
non-programmed	O
exposure	O
modes	O
to	O
detect	O
"	O
out	O
of	O
range	O
"	O
conditions	O
;	O
the	O
"	O
out	O
of	O
range	O
"	O
warning	O
feature	O
was	O
dropped	O
on	O
later	O
models	O
,	O
reportedly	O
due	O
to	O
patent	O
conflicts	O
.	O
</s>
<s>
Evaluative-Through	O
The	O
Lens	O
(	O
E-TTL	O
)	O
is	O
a	O
Canon	B-Algorithm
EOS	I-Algorithm
flash	O
exposure	O
system	O
that	O
uses	O
a	O
brief	O
pre-flash	O
before	O
the	O
main	O
flash	O
in	O
order	O
to	O
obtain	O
a	O
more	O
correct	O
exposure	O
.	O
</s>
<s>
Unlike	O
TTL	O
and	O
A-TTL	B-Algorithm
metering	O
,	O
which	O
use	O
a	O
dedicated	O
flash	O
metering	O
sensor	O
mounted	O
in	O
the	O
base	O
of	O
the	O
mirror	O
box	O
,	O
E-TTL	O
uses	O
the	O
same	O
evaluative	O
metering	O
sensor	O
used	O
for	O
ambient	O
metering	O
.	O
</s>
<s>
Like	O
TTL	O
(	O
and	O
like	O
the	O
actual	O
flash	O
metering	O
,	O
but	O
not	O
the	O
pre-flash	O
,	O
of	O
A-TTL	B-Algorithm
)	O
,	O
the	O
sensor	O
is	O
internal	O
to	O
the	O
camera	O
and	O
takes	O
its	O
exposure	O
via	O
the	O
lens	O
so	O
any	O
filters	O
added	O
to	O
the	O
lens	O
will	O
also	O
affect	O
the	O
E-TTL	O
readings	O
giving	O
more	O
accurate	O
exposure	O
information	O
to	O
the	O
camera	O
.	O
</s>
<s>
E-TTL	O
II	O
is	O
a	O
software	O
improvement	O
on	O
E-TTL	O
and	O
is	O
now	O
a	O
standard	O
in	O
all	O
EOS	B-Algorithm
cameras	I-Algorithm
introduced	O
with	O
or	O
after	O
the	O
Canon	B-Device
EOS-1D	I-Device
Mark	I-Device
II	I-Device
in	O
2004	O
.	O
</s>
<s>
Speedlite	O
is	O
the	O
trade	O
name	O
for	O
Canon	O
's	O
line	O
of	O
external	O
flashes	O
for	O
use	O
with	O
their	O
EOS	B-Algorithm
line	I-Algorithm
of	I-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
Introduced	O
in	O
autumn	O
2012	O
,	O
the	O
Speedlite	O
90EX	O
is	O
a	O
very	O
small	O
unit	O
designed	O
specifically	O
for	O
the	O
company	O
's	O
first	O
mirrorless	B-Device
interchangeable-lens	I-Device
camera	I-Device
,	O
the	O
EOS	B-Algorithm
M	I-Algorithm
.	O
It	O
runs	O
off	O
two	O
AAA	O
batteries	O
,	O
and	O
can	O
serve	O
as	O
a	O
wireless	O
flash	O
controller	O
.	O
</s>
<s>
At	O
introduction	O
,	O
the	O
90EX	O
was	O
bundled	O
with	O
all	O
EOS	B-Algorithm
M	I-Algorithm
kits	O
sold	O
in	O
the	O
EU	O
,	O
though	O
not	O
in	O
the	O
U.S.	O
</s>
<s>
It	O
is	O
the	O
first	O
E-TTL	O
unit	O
from	O
Canon	O
sold	O
as	O
a	O
dedicated	O
flash	O
for	O
the	O
first	O
E-TTL	O
cameras	O
-	O
EOS	B-Algorithm
50	O
(	O
Elan	O
II	O
)	O
and	O
EOS	B-Algorithm
50e	O
(	O
Elan	O
IIe	O
)	O
,	O
which	O
were	O
introduced	O
in	O
1995	O
.	O
</s>
<s>
The	O
Speedlite	O
430EX	O
and	O
Speedlite	O
430EX	O
II	O
are	O
external	O
flashes	O
made	O
by	O
Canon	O
for	O
use	O
with	O
their	O
EOS	B-Algorithm
line	I-Algorithm
of	I-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
The	O
Speedlite	O
470EX-AI	O
is	O
an	O
external	O
flash	O
made	O
by	O
Canon	O
for	O
use	O
with	O
their	O
EOS	B-Algorithm
line	I-Algorithm
of	I-Algorithm
cameras	I-Algorithm
that	O
was	O
announced	O
on	O
February	O
25	O
,	O
2018	O
.	O
</s>
<s>
The	O
Speedlite	O
550EX	O
(	O
introduced	O
September	O
1998	O
)	O
is	O
a	O
flash	O
made	O
by	O
Canon	O
for	O
use	O
with	O
their	O
EOS	B-Algorithm
line	I-Algorithm
of	I-Algorithm
cameras	I-Algorithm
,	O
primarily	O
the	O
Canon	B-Algorithm
EOS	I-Algorithm
3	I-Algorithm
.	O
</s>
<s>
The	O
Speedlite	O
580EX	O
(	O
introduced	O
in	O
2004	O
with	O
a	O
price	O
of	O
$480	O
)	O
and	O
Speedlite	O
580EX	O
II	O
are	O
flashes	O
made	O
by	O
Canon	O
for	O
use	O
with	O
their	O
EOS	B-Algorithm
line	I-Algorithm
of	I-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
However	O
some	O
better	O
features	O
on	O
the	O
earlier	O
model	O
were	O
dropped	O
like	O
EL	O
backlight	O
on	O
the	O
LCD	O
(	O
580EX	O
II	O
uses	O
simple	O
led	O
back-light	O
)	O
and	O
designated	O
master/slave	B-Operating_System
switch	O
.	O
</s>
<s>
The	O
Speedlite	O
600EX-RT	O
was	O
announced	O
on	O
March	O
2	O
,	O
2012	O
alongside	O
the	O
new	O
Canon	B-Algorithm
EOS	I-Algorithm
5D	I-Algorithm
Mark	I-Algorithm
III	I-Algorithm
.	O
</s>
<s>
New	O
features	O
include	O
rechargeable	O
Li-ion	O
Battery	O
Pack	O
(	O
LP-EL	O
)	O
,	O
upgraded	O
Xenon	O
Flash	O
tube	O
and	O
internal	O
cooling	O
system	O
,	O
as	O
well	O
as	O
dust	O
-	O
and	O
water-resistance	O
of	O
the	O
same	O
standard	O
as	O
found	O
on	O
Canon	O
's	O
EOS-1D	O
camera	O
.	O
</s>
<s>
The	O
ST-E10	O
was	O
introduced	O
in	O
September	O
,	O
2021	O
along	O
with	O
the	O
EOS	B-Algorithm
R3	O
,	O
as	O
a	O
small	O
,	O
lightweight	O
radio	O
flash	O
controller	O
for	O
cameras	O
having	O
the	O
Multi-Function	O
Shoe	O
.	O
</s>
