<s>
The	O
Canon	O
EF	O
is	O
a	O
manual	O
focus	O
35mm	O
single-lens	B-Algorithm
reflex	I-Algorithm
camera	I-Algorithm
produced	O
by	O
Canon	O
between	O
1973	O
and	O
1978	O
.	O
</s>
<s>
It	O
was	O
compatible	O
with	O
Canon	O
's	O
FD-mount	B-Algorithm
lenses	O
.	O
</s>
<s>
The	O
EF	O
was	O
built	O
as	O
an	O
electro-mechanical	O
version	O
of	O
Canon	O
's	O
top-of-the	O
line	O
wholly	O
mechanical	O
Canon	B-Algorithm
F-1	I-Algorithm
.	O
</s>
<s>
The	O
Canon	O
EF	O
could	O
operate	O
"	O
Variable	O
Aperture	B-General_Concept
AE	O
"	O
mode	O
(	O
commonly	O
called	O
shutter	B-Algorithm
priority	I-Algorithm
)	O
or	O
full	O
manual	O
mode	O
,	O
where	O
the	O
operator	O
would	O
control	O
both	O
the	O
shutter	O
speed	O
and	O
the	O
aperture	B-General_Concept
.	O
</s>
<s>
When	O
used	O
in	O
automatic	O
mode	O
,	O
it	O
's	O
possible	O
to	O
lock	O
the	O
current	O
aperture	B-General_Concept
value	O
,	O
then	O
recompose	O
the	O
picture	O
,	O
if	O
desired	O
,	O
by	O
pressing	O
the	O
small	O
silver	O
button	O
next	O
to	O
the	O
film	O
rewind	O
knob	O
.	O
</s>
<s>
Automatic	O
exposure	O
required	O
the	O
FD-mount	B-Algorithm
lenses	O
.	O
</s>
<s>
In	O
1975	O
,	O
the	O
range	O
of	O
FD	B-Algorithm
lenses	I-Algorithm
available	O
spanned	O
from	O
15mm	O
fisheye	O
to	O
300mm	O
telephoto	O
,	O
including	O
three	O
zoom	O
lenses	O
.	O
</s>
<s>
Using	O
manual	O
exposure	O
and	O
stopped	O
down	O
metering	O
,	O
the	O
Canon	O
EF	O
could	O
also	O
be	O
used	O
with	O
the	O
older	O
FL-mount	B-Algorithm
and	O
R-mount	B-Algorithm
lenses	O
.	O
</s>
<s>
The	O
EF	O
used	O
a	O
unique	O
shutter	O
among	O
Canon	O
's	O
35mm	O
SLRs	B-Algorithm
:	O
a	O
Copal	O
Square	O
vertical-travel	O
metal	O
blade	O
focal	O
plane	O
shutter	O
.	O
</s>
<s>
To	O
the	O
right	O
is	O
a	O
scale	O
with	O
the	O
aperture	B-General_Concept
setting	O
,	O
where	O
a	O
needle	O
points	O
at	O
the	O
aperture	B-General_Concept
the	O
camera	O
's	O
exposure	O
meter	O
selects	O
,	O
and	O
also	O
automatically	O
sets	O
,	O
provided	O
the	O
FD	B-Algorithm
lens	I-Algorithm
or	O
FD	B-Algorithm
new	I-Algorithm
lens	I-Algorithm
is	O
set	O
to	O
the	O
green	O
A	O
symbol	O
(	O
or	O
green	O
on	O
older	O
lenses	O
)	O
.	O
</s>
<s>
The	O
range	O
goes	O
from	O
1.2	O
to	O
5.6	O
,	O
in	O
order	O
to	O
suit	O
lenses	O
from	O
the	O
Canon	B-Algorithm
FD	I-Algorithm
55	O
mm	O
1:1.2	O
ASPHERICAL	O
S.S.C.	O
</s>
<s>
to	O
the	O
Canon	B-Algorithm
FD	I-Algorithm
300	O
mm	O
1:5.6	O
S.C.	O
</s>
<s>
The	O
smallest	O
aperture	B-General_Concept
is	O
not	O
adjusted	O
for	O
.	O
</s>
<s>
The	O
camera	O
always	O
displays	O
apertures	B-General_Concept
up	O
to	O
f/22	O
,	O
but	O
with	O
a	O
red	O
line	O
down	O
to	O
f/16	O
,	O
to	O
remind	O
the	O
user	O
that	O
some	O
lenses	O
,	O
like	O
the	O
Canon	B-Algorithm
FD	I-Algorithm
50	O
mm	O
1:1.4	O
S.S.C.	O
</s>
<s>
has	O
its	O
smallest	O
aperture	B-General_Concept
at	O
f/16	O
,	O
while	O
some	O
,	O
like	O
the	O
Canon	B-Algorithm
FD	I-Algorithm
135	O
mm	O
1:2.5	O
S.C.	O
can	O
stop	O
down	O
to	O
f/22	O
.	O
</s>
<s>
Later	O
,	O
when	O
the	O
Canon	B-Algorithm
FD	I-Algorithm
new	I-Algorithm
lenses	O
became	O
available	O
,	O
the	O
camera	O
could	O
n't	O
properly	O
represent	O
the	O
new	O
smallest	O
aperture	B-General_Concept
,	O
like	O
f/32	O
.	O
</s>
<s>
Due	O
to	O
corrections	O
taken	O
for	O
proper	O
exposure	O
with	O
full	O
aperture	B-General_Concept
metering	O
,	O
stopped	O
down	O
metering	O
with	O
larger	O
apertures	B-General_Concept
than	O
f/2.8	O
was	O
not	O
reliable	O
.	O
</s>
<s>
Like	O
all	O
pre-1987	O
Canon	O
SLR	B-Algorithm
's	O
,	O
the	O
EF	O
accepted	O
Canon	B-Algorithm
FD	I-Algorithm
mount	I-Algorithm
lenses	O
.	O
</s>
<s>
Stopped	O
down	O
metering	O
must	O
be	O
used	O
with	O
older	O
Canon	B-Algorithm
FL	I-Algorithm
lenses	O
.	O
</s>
