Please do not panic and do not return your lens. In the majority of cases, there is nothing wrong with your lens; each lens is manufactured in exactly the same way and adjusted on an optical collimator which is used to calibrate the lens, check if all elements are aligned optically and to set elements at the proper focus. The issue of front and/or back focusing, most likely, comes as a result of the viewfinder focusing system which varies in each and every camera. This is a quick solution to this situation.
If you are experiencing front and/or back focusing issues, we urge you use the “AF fine tune” or “Microfocus Adjustment in your camera’s menu to calibrate your lens to the camera. If this feature is not available in your camera’s menu we will ask you to send the lens to us and we will rewrite the AF Data to accommodate for the variation in your camera’s viewfinder focusing system; essentially, calibrating your lens to your camera. This will be done within a 48 hours of receiving your equipment in our headquarters; 15 Fleetwood Ct. Ronkonkoma, NY 11779 Attn: Service dept. During the Warranty period of the product (subject to warranty eligibility), there is no charge for this service and we cover the cost of the return 3 day ground shipping back to you.
In 2013 Sigma introduced our Global Vision lens line along with the USB dock, an accessory sold separately allowing you to calibrate the AF Data of any Global Vision lens. To find out more information, consult the USB dock page.