The dedicated 2x APO Teleconverter features a 6 element/5 group optical design, and it is specifically designed for use with longer telephoto and telezoom lenses.

The high performance optical characteristics of these teleconverters maintain the optical performance of the compatible lenses with which they can be used. 

Sigma APO Tele Converter 1.4x and 2x are dedicated Tele Converter lenses, which should be used only with the listed lenses. 
The 2x Convertor will fit the following lenses 180mm f/3.5 APO MACRO Ex HSM - MF 
300mm f/2.8 APO Ex HSM - AF 

300mm f/4.0 APO MACRO - MF 
400mm f/5.6 APO MACRO /HSM - MF 
500mm f/4.5 APO Ex HSM - MF 
800mm f/ 5.6 Ex HSM - MF 
70-200mm f/2.8 Ex HSM - AF 
70-210mm f/2.8 - MF 
50-500mm f/4-6.3 APO - MF 
100-300mm f/4 Ex HSM - MF 
120-300mm f/2.8 Ex APO - AF 
300-800mm f/5.6 Ex APO - MF 
Will also fit the following Orginal Canon EF Lenses 
200mm f2.8L USM - AF 
300mm f2.8L USM - AF 
300mm f4.0L IS - MF 
400mm f2.8L USM - AF 
400mm f5.6L USM - MF 
500mm f4.5L USM - MF 
600mm f/4L - MF 
70-200mm f2.8L USM - AF 

On the lists, the lenses marked "AF" will retain auto focus operation when used with a Tele Converter. The lenses marked "MF can only be used for manual focus. 

Please refer to the manufacturers Teleconverer Matching List for an updated compatability chart. 
http://www.sigma-photo.co.jp/english/acc/condaitr.htm 

The Sigma 2x APO Tele-Converter is commonly used for Wildlife and more.The Sigma 2x APO Tele-Converter is most used by customers who consider themselves to be a Photo enthusiast, Semi-pro photographer among others.The Sigma 2x APO Tele-Converter is popular because customers like the following qualities of the Sigma 2x APO Tele-Converter: Durable, Easy to use and Improves function

Construction

5 Groups /6 Elements

Dimensions (Length x Diameter)

68 x 45.3mm / 2.6 x 1.78"

Weight

234g / 8.3oz.

• Front & Rear Lens Caps
• Soft Case
• Brand New Factory Fresh Import Model