Low-cost Lens-SIGMA 70-300mm DG MACRO

Sigma’s 70-300mm F4-5.6 DG Macro is a compact telephoto zoom lens.

You certainly can’t accuse this Sigma lens of being overpriced, yet it boasts some clever tricks. Most notably, it has a ‘macro’ facility which is available via a switch on the lens barrel. This reduces the close-focusing range from 1.5m to just 0.95m
in the 200-300mm sector of the zoom range. Thus if you combine the longest zoom setting with the shortest focus
distance, you can get as much as 0.5x macro magnification.

Optical highlights include an SLD (Special Low Dispersion) glass element to reduce colour fringing, and a nine-blade diaphragm that gives better-rounded apertures than the Canon lenses.

One unwelcome omission,shared by some of the other lenses on test, is the lack of an optical stabilizer. This makes
it very difficult to achieve consistently sharp handheld shots, especially when used on an APS-C format camera that
boosts the effective maximum focal length to 480mm. The basic electric motor that drives  the autofocus system is also
quite loud, and the manual focus ring rotates during autofocus, as is the case with
many of these lenses.
Performance Lens-SIGMA 70-300mm DG MACRO
Aside from the noisy and somewhat sluggish autofocus system, overall performance is reasonable for such a low-cost
lens. Image quality is pretty average in most respects but,while sharpness is very good at the short end of the zoom
range, it drops off considerably at 300mm.

Source: sigma , digitalcameraworld