The
18–50mm 2.8 EX DC Macro is a consumer-level lens. It is constructed with a plastic body and a metal mount. The lens features a distance window with
depth of field scale. A 7-blade, maximum
aperture of 2.8 gives the lens the ability to create depth of field effects. The optical construction of the lens contains 15 lens elements, including two
aspherical lens elements, one SLD (Special Low
Dispersion) element, and one ELD (Extraordinary Low Dispersion) element. The lens uses an internal focusing system, powered by a micro motor.
Auto focus speed of this lens is moderate, but because of its focal length, auto focus time is not long. The front of the lens does not rotate, but the focusing ring does, when using auto focus. The lens uses an extending inner lens barrel when zooming; this allows a more compact design, and does not rotate while zooming.
HSM variant In 2007, Sigma released a HSM version of the
18–50mm 2.8 EX DC Macro, called the
18–50mm 2.8 EX DC Macro HSM. This lens is available for Nikon F-mount only. The lens has the same optical formula as the non-HSM lens, but is 0.5 mm shorter, and 85 g (18.9 oz.) heavier. The lens has a closer minimum focus distance of 20 cm, but because of the larger
Nikon DX sensor size, the magnification rating is still 1:3. Also because of larger sensor size, the stated angle of view is 76.5°–31.7°, though these angles are still obtainable on the non-HSM version. ==See also==