The Sigma 24-70mm F2.8 DG HSM OS Art is a premium workhorse zoom lens designed for the latest high megapixel DSLRs. A constant aperture of 2.8 through the zoom range makes this a highly versatile tool and a brand new Optical Stabilization (OS) system helps compensate for camera shake. Though a common focal length, the Sigma 24-70mm Art brings a new level of usability and durability featuring a rugged metal barrel and an emphasis on image quality. Building off the experience from the 12-24mm Art, the aspherical elements used in the 24-70mm F2.8 OS Art undergo a highly precise level of polishing, producing elements thicker in the center than on the edges. This process creates stunning image quality and beautiful circular bokeh.
What photographers demand from the 24-70mm F2.8 specification is much more than outstanding image quality. They want all the features that make this a go-to lens for a wide range of photographic opportunities, including optical design ideal for the latest ultra-high-megapixel digital cameras, hypersonic motor (HSM) for high-speed autofocus, optical stabilizer (OS) with powerful stabilization effect, dust- and splash-proof mount with rubber sealing, and a metal barrel for a stable, rigid feel. This all-new 24-70mm F2.8 lens from SIGMA delivers the performance and functionality that help pros succeed in news, nature, and many other fields of photography.
SIGMA is organizing all its interchangeable lenses into three product lines: Contemporary, Art, and Sports, each with a distinctive concept. Designed with a focus on sophisticated optical performance and abundant expressive power, our Art line lenses deliver high-level artistic expression. Offering astonishing rendering performance that meets the highest standard, they are perfect for landscapes, portraits, still-lifes, close-ups, and casual snaps. They are made for the kind of photography that unleashes the inner artist. A powerful ally in every genre of photography, SIGMA's Art line lenses excel both in the studio for formal works and outdoors for impressive shots of architecture, starry skies, and many other scenes.
To fulfill the uncompromising image quality standard of the Art line, this lens features a power distribution that has been optimized in exacting detail. This is the lens for those who desire consistent resolution at maximum F2.8 brightness or lower and complete control of the beautiful bokeh effect.
Three SLD glass lens elements and four aspherical lens elements help minimize optical aberrations. To ensure outstanding image quality from the center to the edges of the photograph, the optical system minimizes coma, which causes points of light to streak, and transverse chromatic aberration, which cannot be corrected by adjusting the aperture. The optical system also minimizes distortion, which can be particularly evident in wide-angle shots, resulting in excellent optical performance throughout the zoom range.
Aspherical lenses necessitate refined expertise in the design and manufacturing of advanced, high-performance lenses. SIGMA’s representative products to feature this technology were the SIGMA 12-24mm F4 DG HSM | Art and SIGMA 14mm F1.8 DG HSM | Art, which both incorporated large ⌀80mm aspherical lenses as their front lens element.
Building on the success of these predecessors, the SIGMA 24-70mm F2.8 DG OS HSM | Art incorporates an aspherical lens element that helps achieve extremely high resolution. This element is much thicker at the center than the edges, and forming its unusual shape is a feat of manufacturing technology. Moreover, SIGMA processes the surface of this aspherical lens element with ultra-precise tolerances that are measured in hundredths of a micrometer. This extremely fine surface allows the SIGMA 24-70mm F2.8 DG OS HSM | Art to deliver a very natural and smooth bokeh effect, without the visible concentric rings that afflict typical aspherical lens elements.
SIGMA has continuously pioneered 24-70mm F2.8 lenses that are a step ahead of the times. The first model of this specification, SIGMA 24-70mm F2.8 EX DG ASPHERICAL DF, launched in 2001. Representing the fourth generation of the family, the new SIGMA 24-70mm F2.8 DG OS HSM | Art accomplishes a challenging feat in optical design: incorporating optical stabilizer functionality in a large-diameter standard zoom. By leveraging all of its design and manufacturing expertise, SIGMA has ensured that this new lens fulfills the uncompromising requirements of the Art line for image and build quality.
At wide-open aperture, this lens offers outstanding photographic expression. The area in focus is extremely sharp, while the background exhibits a beautiful bokeh effect with only slight spherical aberration. Since large-diameter zoom lenses are often used at wide-open aperture, SIGMA has paid close attention to the shape of the bokeh, aiming for perfect circularity.
The degree to which light is refracted by glass depends on the light's wavelength. 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. Yet residual chromatic aberration known as “secondary spectrum” may still remain. To minimize this secondary spectrum, which can be a serious issue with conventional lenses, SIGMA lenses feature up to three types of exclusive low-dispersion glass offering superior performance: ELD (Extraordinary Low Dispersion), SLD (Special Low Dispersion) and FLD (“F” Low Dispersion). In particular, FLD glass offers ultra-low dispersion in combination with high transmittance and the anomalous dispersion characteristics of fluorite. Meticulous deployment of these types of exclusive low-dispersion glass and optimization of power distribution gives SIGMA lenses superlative image rendition undiminished by residual chromatic aberration.
From the start of the design process, SIGMA measured flare and ghosting to establish an optical design that is resistant to strong incidental light sources such as backlight. At the prototyping stage, SIGMA used not only simulations but actual photographic experiments to assess flare and ghosting under multiple criteria, identify the causes of these issues under a wide range of situations, and take measures to mitigate them. In addition, SIGMA’s Super Multi-Layer Coating helps further reduce flare and ghosting and provide sharp, high-contrast images even in backlit conditions.
For more information please visit the Sigma website