To develop a large aperture zoom lens with a maximum aperture of F1.8, it was necessary to solve a variety of technical challenges. As the f-number decreases, so does the depth of focus, making it extremely difficult to minimize spherical aberration, axial chromatic aberration, astigmatism and field curvature. To minimize astigmatism across the zoom range, Sigma leveraged its extensive experience in reducing optical aberrations and designing advanced structural elements. Ongoing technological innovation at Sigma's Aizu Factory has also contributed to further enhancements in lens production. Advanced production technologies have made possible a large-diameter molded glass aspheric lens, which teams up with SLD (Special Low Dispersion) glass elements to optimize power distribution and minimize axial chromatic and spherical aberration and field curvature. Thanks to its hard-earned knowledge of lens design and advanced lens manufacturing techniques, Sigma has succeeded in creating a lens that offers F1.8 throughout the zoom range, as well as exceptional image quality at wide open aperture.
When photographing with point light sources such as electric lights or reflections on a body of water in the background, the rounded 9-blade diaphragm helps produce an attractive bokeh effect — even at large-aperture settings.
Zoom lenses are extremely convenient, providing a wide range of angles of view with just a twist of the zoom ring. The downside, however, is that F2.8 has been the limit of zoom lens brightness, forcing photographers to select fixed focal length lenses for brighter f-numbers. Although fixed focal lenses have been superior to zoom lenses in terms of f-number brightness and overall performance, they offer only a fixed angle of view, requiring photographers to carry several with them and change lenses as necessary. The 18-35mm F1.8 DC HSM next-generation large-aperture standard zoom lens is the world's first to deliver F1.8 brightness throughout the zoom range. Its bright viewfinder makes it easy to confirm focus and compose perfect shots. As compared to a F2.8 lens in the same photographic conditions, it allows the photographer to use a shutter speed that is one stop faster, reducing the influence of camera shake. In addition, the shallower depth of field makes possible a beautiful bokeh effect in the background, expanding photographic creativity. From wide open to standard apertures, this lens is highly flexible, covering the angles of view offered by multiple large-aperture, fixed focal length lenses.
All lenses in Sigma's new Art line come with a hood with a high-quality rubberized connector and feature a newly designed lens cap and AF/MF switch, and are designed for intuitive use and superior functionality. Inside, HSM (Hyper Sonic Motor) delivers high AF speed and extremely quiet performance. An enhanced algorithm offers even smoother automatic focusing. Full-time manual focus override is another key feature that leaves the artistic touches in the photographer's hands. The brass mount combines high precision with rugged construction. Its treated surfaces and enhanced strength contribute to the exceptional durability of the lens. In both the external and internal parts, the optimized use of TSC* (Thermally Stable Composite), an excellent match for metal parts, further contributes to the high-precision construction of the lens.
*TSC (Thermally Stable Composite) is a type of polycarbonate with a thermal expansion rate similar to that of aluminum. It has high affinity to metal parts which contributes to high quality product manufacturing.
HSM (Hyper Sonic Motor) delivers high AF speed and extremely quiet performance. An optimized algorithm offers even smoother automatic focusing, and full-time manual focus override is another key feature.
The lens incorporates a rear focus system that prevents focus-dependent variation in aberration, making high-level image quality possible throughout the entire image. With their unchanging barrel length, these lenses also enhance balance and stability for the photographer. Furthermore, since the front of the lens does not rotate, polarizing filters can be used with extra convenience.
From an early stage in the lens design process, flare and ghosting have been measured to establish an optical design resistant to strong incident light sources such as backlighting. Sigma’s Super Multi-Layer Coating reduces flare and ghosting to help photographers produce sharp and high contrast images even in backlit conditions. The included lens hood can be attached to block out extraneous light, which can have a negative effect on rendering performance.
The brass mount combines high precision with rugged construction. Its treated surfaces and enhanced strength contribute to the exceptional durability of the lens.