Sigma Full Line Catalog - page 24

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Original technology minimizes
secondary spectrum
Exclusive low-dispersion glass
The degree to which light is refracted (bent) by glass
depends on the light’s wavelength (color). This fact
causes different colors of light to focus at slightly
different points. The result is chromatic aberration,
the color fringing that is particularly noticeable in
telephoto lenses. Most chromatic aberration can be
removed by combining a high-refractivity convex lens
element with a low-refractivity concave element. But
residual chromatic aberration known as “second-
ary spectrum” can only be corrected with selected
low-dispersion glass materials.
In addition to ELD (Extraordinary Low Dispersion)
glass and SLD (Special Low Dispersion) glass, Sigma
uses FLD (“F” Low Dispersion) glass, which has the
highly desirable anomalous dispersion charac-
teristics of fluorite. Careful arrangement of these
exclusive low-dispersion glass elements gives Sigma
lenses superlative image rendition untarnished by
residual chromatic aberration.
Effective correction of spherical aberration
and distortion
Aspherical lens
Sigma’s aspherical lens technology contributes
to outstanding optical performance and compact
dimensions. These aspherical lens elements com-
pensate for the spherical aberration and distortion
which cannot be completely eliminated using con-
ventional spherical lens elements alone. They are
also key to reducing the size and weight of high-pow-
er zooms and other large lenses while improving im-
age quality. Sigma has two kinds of aspherical lens
technologies. Hybrid aspherical lens elements are
made by forming a polymer in an aspherical shape
on a glass lens surface. Precision-molded glass
aspherical lens elements are made by direct forming
of the glass lens material.
SLD,ELDorFLDglasselement
Smallsecondaryspectrum
Largesecondaryspectrum
Ordinaryglass
Chromatic Aberration Correction
Proprietary multi-layer coating technology
that virtually eliminates ghosting and flare
Super Multi-Layer Coating
Sigma’s own Super Multi-Layer Coating suppresses
flare and ghosting by preventing reflections within
the lens. All DG and DC lenses in the current Sigma
range feature this original technology. In digital
cameras, flare and ghosting may also be caused by
reflections between the image sensor and lens sur-
faces. Here too, Sigma’s Super Multi-Layer Coating
is highly effective, assuring images of outstanding
contrast.
Advanced focusing mechanism that reduces
lens movement and aberration variation
Floating system
This system adjusts the distance between lens
groups during focusing, thereby reducing the amount
of lens movement required. The result is less vari-
ation in aberration at different shooting distances.
The benefits are particularly great in macro lenses,
since they cover a wide range of shooting distances,
as well as in wide-angle SLR camera lenses that em-
ploy asymmetric configurations of lens elements.
Focus systems for optimized performance
Inner and rear focus
In a conventional lens, focusing requires an exten-
sion of the entire lens or the front lens group. How-
ever, to better accommodate autofocusing mecha-
nisms and closeup photography, a need has arisen
for lenses that do not change their length during
focusing or suffer from focus-dependent variation
in aberration. Therefore, Sigma has developed fo-
cusing systems that only move elements within the
lens barrel. These incorporate smaller and lighter
moving lens elements, which help improve autofocus
speed. With their unchanging barrel length and small
variation in center of gravity, these lenses also offer
enhanced balance and stability. Furthermore, since
the front of the lens does not rotate, it is easy to use
polarizing filters.
Floating System
MACRO50mmF2.8EXDG
28mmF1.8EXDGASPHERICALMACRO
Original Sigma technology
that counteracts camera shake
Optical Stabilizer (OS)
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 the detected
movement, thereby minimizing the blur caused by
camera shake. In addition, since stabilization takes
place within the lens, what you see in the viewfinder
is the resulting stabilized image. As a result, you can
confidently judge focus and composition. Two OS
modes are available, depending on the lens. Mode
1 detects and corrects vertical and horizontal mo-
tion, making it 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.
APO70-200mmF2.8EXDGOSHSM
18-250mmF3.5-6.3DCMACROOSHSM
Inner Focus System
20mmF1.8EXDGASPHERICALRF
Rear Focus System
SIGMA LENS TECHNOLOGY
Our lenses are packed with advanced and unique technologies,
which we have developed over the decades as the lens expert.
Camera shake correction mechanism OFF
Camera shake correction mechanism ON
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