||The aspherical lens complex allows freedom of design, improved performance, a reduced number of component lenses and a compact size. This lens provides high optical performance while maintaining a compact size. For example, the 12-24 mm F4.5-5.6 EX DG ASPHERICAL lens widens the range of wide-angle lenses, and it provides distortion-free images with image reproduction performance equivalent to that of a single focal length lens. Aspherical lenses allow the production of high-quality images from compact, lightweight telephoto zoom lenses.
||In order to attain the highest quality images, the APO lens has been made using special low-dispersion (SLD) glass and is designed to minimize color aberration. SIGMA's APO zoom lenses minimize color aberration. As the refractive index of glass depends on the wavelength of light, color aberration occurs when different colors form images at different points. This problem often occurs with telephoto lenses, but the Special Low-Dispersion (SLD) glass and Extraordinary Low Dispersion (ELD) used in SIGMA's APO lenses helps to compensate for color aberration, thereby allowing them to produce of sharp images.
||OS (Optical Stabilizer) Function
||This function utilizes a built-in mechanism that compensates for camera shake. It dramatically expands photographic possibilities by alleviating camera movement when shooting by hand held camera. Developed with Sigma's own technology, the OS (Optical Stabilizer) function uses two sensors inside the lens to detect both vertical and horizontal movement of the camera. This function, which works by moving an optical image stabilizing lens group, to effectively compensate for camera shake, helps to set our lenses apart from the rest. To handle all types of shooting conditions, the system has two optical stabilizer modes. Mode 1 determines camera shake in vertical and horizontal panning and compensates for image blurring. It is therefore effective for taking general photography or for shooting landscapes and other static subjects. Mode 2 detects vertical camera shake and compensates for blurring. It is effective for panning the camera to photograph moving subjects such as motor sports.
||APO Teleconverter EX
||This lens can be used with the APO Teleconverter EX. It can increase the focal length and will interface with the camera's AE (automatic exposure) function.
||The exterior of this lens is EX-finished to denote the superior build and optical quality, and to enhance its appearance.
|| Hyper-Sonic Motor
||This lens uses a motor driven by ultrasonic waves to provide a quiet, highspeed AF.
||To ensure stability in focusing, this lens moves the inner lens group or groups without changing the lens' physical length.
||This lens is equipped with a system that moves the rear lens group for highspeed , silent focusing. Conventional focusing has normally been performed by moving either all lens groups as a fixed unit or only the first lens group. AF cameras are now widely used, even for close-up photography. Consequently, demand has arisen for a focusing system that will keep the length of the lens unchanged while showing little fluctuation of aberration. In response to this demand, SIGMA has developed a new inner focus system that moves two lens groups inside the telephoto and telephoto MACRO lenses. This system has floating elements that substantially improve the close-up capability of the lens. The super wide angle lens having a large front-lens uses a rear focusing system to move the rear-lens apparatus and enhance the floating effect, and the18-125 mm F3.5- 5.6 DC lens uses an inner focusing system to move the secondary lens apparatus. SIGMA has also succeeded in attaining a minimum shooting distance of 19.7 inches/0.5 m throughout the entire zoom range of this lens. The rear focus system ensures high-speed focusing with the APO 135-400 mm F4.5-5.6 DG and APO 170-500 mm F5-6.3 DG telephoto zoom lenses.
||DG Lens for Digital
||The most suitable lenses for 35mm film single-lens reflex cameras, as well as for digital SLR cameras. Sigma's development of the DG (Digital) range of lenses has concentrated on the correction of distortion and aberrations. Magnification of chromatic aberration is particularly conspicuous with digital cameras. The optical designs and cutting-edge technology incorporated by Sigma eliminate flare and ghosting from te image sensor and create excellent color balance. Vignetting is minimized whilst marginal illumination is ensured. These high performance lenses are equally suited for digital and analogue cameras.
||DC Lens for Digital
||These are special lenses designed so that the image circle matches the smaller size of the image sensor of most digital SLR cameras. Their specialized design gives these lenses the ideal properties for digital cameras, the compact and lightweight construction is an added bonus!
||The floating system is used to control the focus. This system moves the different lens groups in the optical system to different positions, thereby minimizing the telescoping distance and the fluctuation of aberration at different shooting distances. This system is particularly effective for macro lenses (which encompass a wide range of shooting distances) and wide angle lenses (for Single-Lens Reflex cameras) whose lens composition is asymmetric. SIGMA uses the floating system for the MACRO 50 mm F2.8EX DG lens and the large-aperture wide-angle 28 mm F1.8 EX DG ASPHERICAL MACRO lenses.
|| DF (Dual Focus) System
||The DF (Dual Focus) system disengages the linkage between the internal focusing mechanism and outer focusing ring when the focusing ring is moved to the AF position. This system provides easy and precise handling of the lens, since the focusing ring does not rotate during autofocusing. The wide focusing ring also enables easy and accurate manual focusing.
||Although telephoto zoom lenses can be used closer to the object than single-focal length telephoto lenses, there is still a minimum shooting distance. SIGMA has made this minimum distance smaller and developed the zoom MACRO lens for taking close-up photographs of the same quality as those taken with a regular MACRO lens, while maintaining the performance specific to an APO lens. Rather than carrying around the cumbersome accessories required for close-up work, the photographer can now take photographs at a magnification of 1:2 (one half life size) using a telephoto lens, by quickly shifting from the normal setting to the full macro setting.