(From Sigma lens literature) This lens has a macro focusing capability with fast ƒ/1.8 maximum aperture, which is ideal for Digital SLR cameras.
This lens is capable of macro photography with a minimum shooting distance of 20cm (7.8 in.) and a maximum reproduction ratio of 1:2.9.
The lens has an advanced optical construction, in order to obtain adequate peripheral brightness when wide-open. Also, the iris diaphragm has 9 blades to obtain beautiful out of focus images in the foreground and background.
The lens incorporates a Dual-Focus (DF) mechanism. It is easy to hold the lens, since the focusing ring does not rotate during auto-focus, yet it provides adequate focusing torque of the focusing ring during manual focusing of the lens. Also, this also allows the use of a Petal-type Hood and the easy use of a polarizing filter.
It incorporates a floating focus system and uses two aspherical lens elements for minimizing distortion, aberration and astigmatism.
