From the Manufacturer
Compact large aperture standard zoom lens equipped with HSM for the latest digital SLR cameras
This large aperture standard zoom lens covers focal lengths from 24mm and is housed in a compact construction. The latest optical design provides a compact construction and is ideal for general photography. ELD (Extraordinary Low Dispersion) glass, two SLD (Special Low Dispersion) glass elements and three aspherical lenses provide excellent correction of all types of aberrations. This lens incorporates HSM (Hyper Sonic Motor), ensuring a quiet and high speed AF as well as full time manual focus capability. This lens has a minimum focusing distance of 38cm/15in and a maximum magnification ratio of 1:5.3. The rounded 9 blades diaphragm creates an attractive blur.
Excellent optical performance
ELD (Extraordinary Low Dispersion) glass, two SLD (Special Low Dispersion) glass elements, two molded glass aspherical lenses and a hybrid aspherical lens provide excellent correction for all type of aberrations. High image quality is assured throughout the entire zoom range.
Large aperture standard zoom lens with compact construction
The lens has a compact construction with an overall length of 94.7mm (3.7"). It is ideal for many situations such as portrait, landscape and general photography.
F2.8 large aperture over the entire zoom range
This lens offers a large aperture of F2.8 over its entire zoom range. It provides freedom of creative expression and is ideal for photography indoors or in dim lighting.
HSM (Hyper Sonic Motor)
HSM indicates lenses equipped with a Hyper Sonic Motor, driven by ultrasonic waves. HSM ensures a quiet and high speed AF as well as full-time manual focus override by rotation of the focus ring.
Inner focusing system
The polygonal shape of a conventional iris diaphragm causes outo-focus light points to appear polygonal. A rounded diaphragm is designed to produce rounded outo-focus light points when opened to near maximum aperture. This creates attractive bokeh effects in many situations, such as when photographing a subject against an out-of-focus surface of water from which light is being reflected.
Reduced Flare and Ghosting
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 surfaces. Here too, Sigma's Super Multi-Layer Coating is highly effective, assuring images of outstanding contrast.
Petal-type hoodThis lens is equipped with a Petal-type hood to block out extraneous light and reduce internal reflections.
In a conventional lens, focusing requires an extension of the entire lens or the front lens group. However, to better accommodate autofocusing mechanisms 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 focusing systems that only move elements within the lens barrel. These incorporate smaller and lighter moving lens elements which help improve auto-focus speed. With their unchanging barrel length and small variation in the center of gravity, 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.
|Lens Construction||14 Elements in 12 Groups|
|Angle of View||84.1 -34.3 degrees|
|Number of Diaphragm Blades||9 Blades|
|Minimum Aperture||F22 (Rounded diaphragm)|
|Minimum Focusing Distance||38cm / 15.0in.|
|Filter Size||Diameter 82mm|
|Dimensions||Diameter 88.6mm x Length 94.7mm / 3.5in. x 3.7in.|
|Weight||790g / 27.9oz.|
MTF (Modular Transfer Function) is one of the measurements that evaluates a lens' performance, and it contrasts sensitivity at different spacial frequencies. The horizontal axis is in millimeters and shows the distance from the center of the image toward the edges, and contrast value (highest value is 1) is shown in the vertical axis.
The readings at 10 lines per millimeter measure the lens' contrast ability (red lines), repeating fine parallel lines spaced at 30 lines per millimeter measure the lens' sharpness ability (green lines), when the aperture is wide open. Fine repeating line sets are created parallel to a diagonal line running from corner to corner of the frame, are called Sagittal lines (S) and sets of repeating lines vertical to these lines are drawn, called Meridional (M) line sets.
effective distortion: When you take a picture of a lattice pattern, it will appear as the blue dotted line shows. the red line illustrates how the lattice pattern will appear in the actual picture when any lens distortion is taken into account.
relative distortion: In this chart, the horizontal axis shows the ideal image height (the distance from the center to the edge of the image [mm]). The vertical axis shows the extent of distortion. The extent of the distortion is represented by how much Y, which is the actual image height, grows (or shrinks) against Y0 which is the ideal image height.
Extent of distortion: D[%]=(Y-Y0/Y0)x100
When you take the picture of a square object, if the distortion amount show a minus value, the image will be seen as expanded (Barrel distortion). If the distortion amount is a plus value, it will be seen as a recessed (pincushi on distortion). When the distortion value is close to 0, the appearance of distortion is very minimal.
The horizontal axis shows the image height (the distance from the center to the edge of the image [mm]). The vertical axis shows the amount of light in the image (based on the amount of light in the image center being 100%). If the peripheral amount of light is lower than the center, the four corners of the image will be darker (vignetting).