Sigma 572955 Specifications download pdf (Page 23)

Furthermore, since the front of the

lens does not rotate, polarizing ﬁlters

can be used with extra convenience.

The Hyper Sonic Motor (HSM) is an

original Sigma development that uses

ultrasonic waves to drive the auto-

focus mechanism. Its extremely quiet

operation helps avoid disturbing

photographic subjects. High torque

and speed assure rapid auto-focus

response. Sigma uses two types of

HSM: Ring HSM and Micro HSM.

The Ring HSM conﬁguration permits

manual ﬁne tuning of focus (manual

override) by turning a focusing ring

after auto-focus operation.

The polygonal shape of a con ven-

tional iris diaphragm causes out-

of-focus light points to appear

polygonal. A rounded diaphragm is

designed to produce rounded out-

of-focus light points when opened to

near maximum aperture.

This creates attractive bokeh eects

in many situations, such as when

photographing a subject against an

out-of-focus surface of water from

which light is being reﬂected.

Sigma’s original Optical Stabilizer

(OS) technology uses two sensors

inside the lens to detect vertical

and horizontal motion.

By adjusting particular lens elements,

the OS compensates for detected

movement, thereby minimizing blur

caused by camera shake. This can

provide stabilization equivalent to

using a shutter speed four stops

faster. Since stabilization takes place

within the lens, what you see in the

viewﬁnder is the resulting stabilized

image. This lets you conﬁdently

judge focus and composition.

Two OS modes are available,

depending on the lens.

Mode 1 detects and corrects vertical

and horizontal motion, ideal for

shooting with the camera in a ﬁxed

position. Mode 2 detects and corrects

only vertical motion, making it ideal

for panning, as when shooting motor

sports, for example.

Camera shake correction mechanism OFF

Camera shake correction mechanism ON

This system adjusts the distance

between lens groups while focusing,

thereby reducing the amount of lens

movement required. The result is less

variation in aberration at dierent

shooting distances. Beneﬁts are

particularly great in macro lenses

because they cover a wide range of

shooting distances, and in wide-angle

lenses which employ asymmetric

conﬁgurations of lens elements.

In a conventional lens, focusing

requires an extension of the entire

lens or the front lens group. However,

to better accommodate auto-

focusing mechanisms and close-

up photography, a need has arisen

for lenses that do not change their

length during focusing or suer

from focus-dependent variation in

aberration. Therefore, Sigma has

developed focusing systems that

only move elements within the lens

barrel. These incorporate smaller and

lighter moving lens elements which

help improve auto-focus speed. With

their unchanging barrel length and

small variation in the center of gravity,

these lenses also enhance balance

and stability for the photographer.

18-200mm F3.5-6.3 DC

APO 70-200mm F2.8 EX DG OS HSM

Inner Focus System

20mm F1.8 EX DG ASPHERICAL RF

Rear Focus System

Floating System

MACRO 50 mm F2.8 EX DG

28 mm F1.8 EX DG ASPHERICAL MACRO

Optical Stabilizer (OS)

Original Sigma technology

counteracts camera shake

Hyper Sonic Motor (HSM)

AF drive motor for rapid focusing

and quiet operation

Rounded Diaphragm

Designed to optimize bokeh

near maximum aperture

Inner and Rear Focus

Focus systems for optimized

performance

Floating System

Advanced focusing mechanism

reduces lens movement and

aberration variation

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