Sigma 18-50mm - This lens has a large aperture of f/2.8 throughout the entire zoom range, a minimum focusing distance of 20cm (7.9") and a maximum magnification of 1:3, making it ideal for close-up photography.

Special Low Dispersion (SLD) and Extraordinary Low Dispersion (ELD) glass elements provide excellent correction of color aberrations.   The super multi-layer lens coating reduces flare and ghosting, a common problem with digital cameras.   High image quality is assured throughout the entire zoom range.

An inner focusing system eliminates front lens rotation, making the lens particularly suitable for using the petal-type lens hood (supplied) plus circular polarizing filters.

Specification

• Lens Construction : 15 Elements in 13 Groups
• Angle of View : 69.3 - 27.9 degrees
• Number of Diaphragm Blades : 7 Blades
• Minimum Aperture : f/22
• Minimum Focusing Distance : 20cm /7.9 in.
• Maximum Magnification : 1:3
• Filter Size Diameter : 72mm
• Dimensions Diameter : 79mm x 85.8mm or 3.1 in. x 3.4 in.
• Weight : 450 grams / 15.9 oz.
• Corresponding AF Mounts : sigma, canon, nikon, sony or minolta, pentax, four-thirds

Comment
An excellent lens to replace your normal Canon EF-S 18-55Mm IS f/3.5-5.6 lens.   Even though this Sigma 18-50mm does not have a stabilizer; it is a fast lens with a reasonable opening of 72mm which can greatly compensate for the stabilizer.   It's a nice walking lens with a average wide angle to normal, much like the normal Canon EF-S 18-55mm walking lens.

Sigma 18-50mm f/2.8 EX DC MACRO does have a little edge compare to the Tamron SP AF 17-50mm f/2.8 XR DiII LD when it comes to filter size, both have good build by the way.  - Even, IF - the Sigma version looks and feel more robust when you hold it.

On the Other hand, Tamron does offer a wider 17mm feature compared to this Sigma's 18mm.

This Sigma 18-50mm f/2.8 EX DC MACRO retails around $ 660.00 US dollar and you might find cheaper price online as well.