<s>
The	O
Sigma	O
8	O
–	O
16mm	O
lens	O
is	O
an	O
enthusiast-level	O
,	O
ultra	O
wide-angle	O
rectilinear	O
zoom	O
lens	O
made	O
by	O
Sigma	O
Corporation	O
specifically	O
for	O
use	O
with	O
APS-C	B-Algorithm
small	O
format	B-Algorithm
digital	B-Device
SLRs	I-Device
.	O
</s>
<s>
It	O
is	O
the	O
first	O
ultrawide	O
rectilinear	O
(	O
non-fisheye	O
lens	O
)	O
zoom	O
lens	O
with	O
a	O
minimum	O
focal	B-Algorithm
length	I-Algorithm
of	O
8mm	O
,	O
designed	O
specifically	O
for	O
APS-C	B-Algorithm
size	O
image	O
sensors	O
.	O
</s>
<s>
At	O
its	O
release	O
it	O
was	O
the	O
widest	O
viewing	B-General_Concept
angle	I-General_Concept
focal	B-Algorithm
length	I-Algorithm
available	O
commercially	O
for	O
APS-C	B-Algorithm
cameras	O
.	O
</s>
<s>
It	O
is	O
part	O
of	O
Sigma	O
's	O
DC	O
(	O
Digital	O
Camera	O
)	O
line	O
of	O
lenses	O
,	O
meaning	O
it	O
was	O
designed	O
to	O
have	O
an	O
image	O
circle	O
tailored	O
to	O
work	O
with	O
APS-C	B-Algorithm
format	B-Algorithm
cameras	O
.	O
</s>
<s>
The	O
lens	O
is	O
sold	O
in	O
versions	O
that	O
fit	O
the	O
bayonet	O
mounts	O
of	O
Nikon	B-Algorithm
,	O
Canon	O
,	O
Sigma	O
,	O
Sony/Minolta	O
and	O
Pentax	B-Application
APS-C	B-Algorithm
cameras	O
.	O
</s>
<s>
It	O
has	O
a	O
bulb-like	O
aspherical	O
lens	O
,	O
similar	O
to	O
notable	O
wide-angle	O
and	O
fisheye	O
lenses	O
such	O
as	O
the	O
Nikon	B-Algorithm
AF-S	O
NIKKOR	O
14-24mm	O
f/2.8G	O
ED	O
,	O
Nikon	B-Algorithm
AF	I-Algorithm
DX	I-Algorithm
Fisheye-Nikkor	I-Algorithm
10.5mm	I-Algorithm
f/2.8G	I-Algorithm
ED	I-Algorithm
,	O
or	O
Tokina	O
AT-X	O
107	O
DX	O
AF	O
10-17mm	O
f/3.5	O
-4.5	O
fisheye	O
lens	O
.	O
</s>
<s>
Over	O
the	O
range	O
of	O
focal	B-Algorithm
lengths	I-Algorithm
,	O
the	O
minimum	O
and	O
maximum	O
aperture	O
vary	O
.	O
</s>
<s>
The	O
lens	O
,	O
which	O
focuses	O
internally	O
,	O
has	O
one	O
of	O
the	O
lowest	O
maximum	O
magnification	O
measurements	O
in	O
its	O
class	O
(	O
which	O
includes	O
the	O
Canon	B-Algorithm
10	I-Algorithm
–	I-Algorithm
18mm	I-Algorithm
and	O
10	B-Algorithm
–	I-Algorithm
22mm	I-Algorithm
,	O
Sigma	O
10	O
–	O
20mm	O
f/3.5	O
and	O
Sigma	O
10	O
–	O
20mm	O
f/4	O
–	O
5.6	O
EX	O
DC	O
HSM	O
,	O
Tamron	O
10	O
–	O
24mm	O
f/3.5	O
–	O
4.5	O
DI	O
II	O
,	O
Nikon	B-Algorithm
10	I-Algorithm
–	I-Algorithm
24mm	I-Algorithm
f/3.5	I-Algorithm
–	I-Algorithm
4.5G	I-Algorithm
ED	I-Algorithm
AF-S	I-Algorithm
DX	I-Algorithm
,	O
and	O
Tokina	O
11	O
–	O
16mm	O
f/2.8	O
AT-X	O
Pro	O
DX	O
lenses	O
)	O
.	O
</s>
<s>
The	O
lens	O
 '	O
autofocus	O
feature	O
is	O
not	O
functional	O
with	O
Pentax	B-Application
ist*	O
series	O
and	O
K100D	B-Algorithm
DSLR	B-Device
cameras	I-Device
that	O
do	O
not	O
support	O
hypersonic	O
zoom	O
mechanics	O
.	O
</s>
<s>
The	O
complex	O
barrel	O
distortion	O
is	O
approximately	O
2.9	O
%	O
at	O
8mm	O
focal	B-Algorithm
length	I-Algorithm
but	O
is	O
fairly	O
insignificant	O
as	O
the	O
focal	B-Algorithm
length	I-Algorithm
is	O
raised	O
above	O
12mm	O
,	O
according	O
to	O
Photozone.de	O
.	O
</s>
<s>
By	O
combining	O
the	O
wide	O
angle	O
focal	B-Algorithm
lengths	I-Algorithm
with	O
narrow	O
apertures	O
,	O
the	O
lens	O
provides	O
strong	O
depth	O
of	O
field	O
rather	O
than	O
making	O
blurred	O
backgrounds	O
.	O
</s>
<s>
As	O
all	O
lens	O
systems	O
,	O
natural	O
vignetting	O
(	O
gradual	O
reduction	O
of	O
an	O
image	O
's	O
brightness	O
from	O
the	O
center	O
towards	O
the	O
periphery	O
)	O
is	O
present	O
due	O
to	O
Lambert	O
's	O
cosine	O
law	O
–	O
this	O
becomes	O
more	O
pronounced	O
at	O
shorter	O
focal	B-Algorithm
lengths	I-Algorithm
.	O
</s>
<s>
For	O
most	O
of	O
the	O
focal	B-Algorithm
length	I-Algorithm
range	O
of	O
the	O
lens	O
,	O
there	O
is	O
between	O
a	O
half	O
stop	O
and	O
third	O
stop	O
of	O
corner	O
shading	O
.	O
</s>
<s>
The	O
lens	O
is	O
equipped	O
with	O
a	O
full-frame	O
digital	O
SLR-compatible	O
mount	O
allowing	O
the	O
usage	O
of	O
both	O
APS-C	B-Algorithm
sized	O
cameras	O
and	O
formats	O
larger	O
than	O
APS-C	B-Algorithm
–	O
the	O
built	O
in	O
lens	O
hood	O
however	O
visibly	O
restricts	O
the	O
field	O
of	O
view	O
(	O
FOV	O
)	O
on	O
formats	O
larger	O
than	O
APS-C	B-Algorithm
–	O
see	O
example	O
above	O
.	O
</s>
<s>
The	O
FOV	O
in	O
APS-C	B-Algorithm
sized	O
cameras	O
is	O
further	O
restricted	O
at	O
shorter	O
focal	B-Algorithm
lengths	I-Algorithm
if	O
the	O
front	O
cap	O
adaptor	O
ring	O
is	O
not	O
removed	O
–	O
see	O
example	O
below	O
.	O
</s>
<s>
The	O
lens	O
 '	O
modulation	O
transfer	O
function	O
(	O
MTF	O
)	O
metrics	O
for	O
its	O
image	B-Algorithm
resolution	I-Algorithm
(	O
sharpness	O
)	O
were	O
described	O
as	O
"	O
surprisingly	O
impressive	O
...	O
throughout	O
the	O
entire	O
zoom	O
range	O
"	O
by	O
Photozone.de	O
.	O
</s>
<s>
Higher	O
focal	B-Algorithm
lengths	I-Algorithm
were	O
less	O
impressive	O
.	O
</s>
<s>
However	O
,	O
stopping	O
down	O
improves	O
the	O
sharpness	O
at	O
all	O
focal	B-Algorithm
lengths	I-Algorithm
,	O
according	O
to	O
PC	O
Magazine	O
.	O
</s>
<s>
At	O
the	O
longer	O
focal	B-Algorithm
lengths	I-Algorithm
for	O
this	O
lens	O
,	O
stopping	O
down	O
to	O
f/29	O
yields	O
a	O
5	O
blur	O
unit	O
result	O
.	O
</s>
<s>
The	O
aperture	O
stop-down	O
focal	B-Algorithm
lengths	I-Algorithm
make	O
the	O
lens	O
a	O
laggard	O
among	O
wide-angle	O
lenses	O
.	O
</s>
<s>
However	O
,	O
DSLR	B-Device
cameras	I-Device
have	O
improved	O
at	O
higher	O
ISO	O
settings	O
.	O
</s>
