The Sigma's construction is the most complex in its class, and includes no fewer than four elements made from Super-Low Dispersion (SLD) glass, along with one formed from fluorite-like 'F' Low Dispersion (FLD) glass, and two aspheric elements. According to Sigma this allows the minimization of an array of aberrations including both longitudinal and lateral chromatic aberration, astigmatism, and field curvature.
The lens also incorporates an ultrasonic-type HyperSonic Motor for fast, quiet autofocus with full-time manual override. This drives a floating inner focus system, that's designed to maintain high image quality at all subject distances. The apertureAPERTUREAperture, shutter speed and ISO form what is known as the exposure triangle in photography. Aperture refers to an opening inside the lens, similar to the iris of your eye, that changes in diameter to control the amount of light that enters a camera. Aperture is expressed in f-stops: the lower the number, the larger the aperture, e.g. f/1.4 is larger than f/8. A larger (or wider) aperture allows more light to pass through the lens to the sensor (film) as a picture is taken, particularly useful in low-light conditions. A larger aperture also produces a shallower depth-of-field, and thus more background blur. diaphragm uses nine curved blades for the attractive rendition of background blur, and Super-Multi-Layer Coating is employed to minimise flareFLAREOccurs when a point light source such as the sun or an artificial light (that is brighter than the rest of the scene), hits the front element of a lens resulting in a lack of contrast, haze, or unwanted semi-transparent objects being present in the image. You can avoid lens flare with a lenshood or filters, however, the effect is also useful for bringing artistic elements into an image, such as sun rays peaking out from behind a rock formation. and ghosting. Sigma says each lens will be individually inspected before leaving the factory, using a measuring system based on its own high-resolution Foveon sensor.