I bought the Sigma 18-250 mm DC OS HSM Zoom to my Nikon D5000. The first copy was bad centered (right side sharp, left out of focus) and very stiff. Brought to Sigma Rödermark to repair the lens. After 10 days, I got another copy back to the words 'for the sake of goodwill exchanged'. The new specimen was much smoother and also the centering was fine. Unfortunately, the lens produced at maximum aperture in the middle zoom range (35 - 135 mm) absolute 'sluggish', low-contrast images; dimmed (from aperture 8) the images were useful. So drove back Rödermark; this time the technician came in person and also asked about the camera around the lens with possible front or back focus must be matched. - After only 2 days I got a new one ('on grounds of fairness ...') and my camera back. The now 3 lens is fine, both mechanically and visually; the HSM provides (with enough light!) quickly and accurately sharp, only the optical stabilizer could work a little more efficiently (Nikon and Tamron also can do better). Overall a good lens that deserves 4 stars; because the Sigma but still the final to the end user (= customers) rolls, only 3 stars! Otherwise, the customer service in Rödermark is very friendly and eager.
