<s>
Aperture	B-Algorithm
priority	I-Algorithm
,	O
often	O
abbreviated	O
A	O
or	O
Av	O
(	O
for	O
aperture	B-General_Concept
value	O
)	O
on	O
a	O
camera	B-Algorithm
mode	I-Algorithm
dial	I-Algorithm
,	O
is	O
a	B-Algorithm
mode	I-Algorithm
on	O
some	O
cameras	O
that	O
allows	O
the	O
user	O
to	O
set	O
a	O
specific	O
aperture	B-General_Concept
value	O
(	O
f-number	O
)	O
while	O
the	O
camera	O
selects	O
a	O
shutter	O
speed	O
to	O
match	O
it	O
that	O
will	O
result	O
in	O
proper	O
exposure	O
based	O
on	O
the	O
lighting	O
conditions	O
as	O
measured	O
by	O
the	O
camera	O
's	O
light	O
meter	O
.	O
</s>
<s>
This	O
is	O
different	O
from	O
manual	O
mode	B-Device
,	O
where	O
the	O
user	O
must	O
decide	O
both	O
values	O
,	O
shutter	B-Algorithm
priority	I-Algorithm
where	O
the	O
user	O
picks	O
a	O
shutter	O
speed	O
with	O
the	O
camera	O
selecting	O
an	O
appropriate	O
aperture	B-General_Concept
,	O
or	O
program	B-Device
mode	I-Device
where	O
the	O
camera	O
selects	O
both	O
.	O
</s>
<s>
As	O
an	O
image	O
's	O
depth	O
of	O
field	O
is	O
inversely	O
proportional	O
to	O
the	O
size	O
of	O
the	O
lens	O
's	O
aperture	B-General_Concept
,	O
aperture	B-Algorithm
priority	I-Algorithm
mode	I-Algorithm
is	O
often	O
used	O
to	O
allow	O
the	O
photographer	O
to	O
control	O
the	O
focus	O
of	O
objects	O
in	O
the	O
frame	O
.	O
</s>
<s>
Aperture	B-Algorithm
priority	I-Algorithm
is	O
therefore	O
useful	O
in	O
landscape	O
photography	O
,	O
for	O
example	O
,	O
where	O
it	O
may	O
be	O
desired	O
that	O
objects	O
in	O
foreground	O
,	O
middle	O
distance	O
,	O
and	O
background	O
all	O
be	O
rendered	O
crisply	O
,	O
while	O
shutter	O
speed	O
is	O
immaterial	O
.	O
</s>
<s>
To	O
obtain	O
this	O
large	O
depth	O
of	O
field	O
,	O
a	O
narrow	O
aperture	B-General_Concept
(	O
identified	O
by	O
a	O
high	O
f-number	O
,	O
e.g.	O
</s>
<s>
Aperture	B-Algorithm
priority	I-Algorithm
mode	I-Algorithm
also	O
finds	O
use	O
in	O
portrait	O
photography	O
,	O
where	O
a	O
wide	O
aperture	B-General_Concept
(	O
identified	O
by	O
a	O
low	O
number	O
,	O
e.g.	O
</s>
<s>
Another	O
common	O
use	O
of	O
aperture	B-Algorithm
priority	I-Algorithm
mode	I-Algorithm
is	O
to	O
indirectly	O
affect	O
shutter	O
speed	O
for	O
a	O
desired	O
effect	O
.	O
</s>
<s>
In	O
landscape	O
photography	O
,	O
a	O
user	O
might	O
select	O
a	O
small	O
aperture	B-General_Concept
when	O
photographing	O
a	O
waterfall	O
,	O
so	O
that	O
the	O
camera	O
will	O
select	O
a	O
slow	O
shutter	O
speed	O
(	O
to	O
allow	O
a	O
sufficient	O
amount	O
of	O
light	O
to	O
reach	O
the	O
film	O
or	O
sensor	B-Algorithm
for	O
proper	O
exposure	O
)	O
,	O
thereby	O
causing	O
the	O
water	O
to	O
blur	O
through	O
the	O
frame	O
.	O
</s>
<s>
At	O
the	O
contrary	O
,	O
a	O
larger	O
aperture	B-General_Concept
allows	O
to	O
shorten	O
the	O
shutter	O
speed	O
reducing	O
the	O
hand	O
jitter	O
by	O
taking	O
a	O
picture	O
without	O
a	O
tripod	O
or	O
,	O
in	O
alternative	O
,	O
a	O
lower	O
ISO	O
to	O
enhance	O
the	O
image	O
quality	O
by	O
reducing	O
the	O
noise	O
.	O
</s>
<s>
When	O
shooting	O
a	O
portrait	O
in	O
dim	O
lighting	O
,	O
the	O
photographer	O
might	O
choose	O
to	O
open	O
the	O
lens	O
to	O
its	O
maximum	O
aperture	B-General_Concept
in	O
hopes	O
of	O
getting	O
enough	O
light	O
for	O
a	O
good	O
exposure	O
while	O
maintaining	O
the	O
shortest	O
possible	O
shutter	O
speed	O
to	O
reduce	O
blur	O
.	O
</s>
