| Sigma
20mm
f1.8
EX
DG
Aspherical
RF
is
one
of
several
EX
Series
lenses.
It
is
the
first
20mm
Super
wide-angle
lens
in
the
world
with
a
large
aperture
of
F1.8
and
angle
of
view
94.5°.
It
has
Macro
focusing
capability
with
a
minimum
focusing
distance
of
20cm/7.9inches
(reproduction
ratio
1:4).
The
iris
diaphragm
has
9
diaphragm
blades
to
obtain
beautiful
out
of
focus
image.
It
incorporates
an
aspherical
lens
element
in
the
front
as
well
as
rear
lens
groups,
to
minimize
distortion,
spherical
aberration
and
astigmatism.
The
lens
has
non-vignetting
optical
construction,
in
order
to
obtain
adequate
peripheral
brightness
with
open
aperture.
This
is
especially
desirable
for
digital
cameras.
The
lens
incorporates
a
rear
focus
system
eliminating
front
lens
rotation,
thus
allowing
the
use
of a
Perfect
Hood
and
easy
use
of
polarizing
filters.
The
lens
also
incorporates
dual-focus
mechanism.
It
is
easy
to
hold
the
lens,
since
the
focusing
ring
does
not
rotate
during auto-focus,
yet
it
provides
adequate
focusing
torque
of
the
focusing
ring
during
manual
focusing
of
the
lens.
The
lens
materials
used
in
this
lens
are
lead
and
arsenic
free
ecological
glass. |
| Construction |
11
groups
/13
elements |
| Angle
of
view |
94.5° |
| F
stop
range |
22 |
| Closest
Focusing
Distance |
20cm
/
7.9" |
| Maximum
Magnification |
1:4 |
| Filter
Size |
82mm |
| Dimensions
(Length
x
Diameter) |
88.5
x
87mm
/
3.5
x
3.4" |
| Weight |
520g
/
18.3oz. |
|
|
|
|
|
