The Adorama 250D/500D series close-up lenses incorporates a double-element achromatic design for maximum optical performance, while the standard 500 series features single-element construction for maximum economy. The 250 close up lenses changes the closest focusing distance from infinity to 250mm/approx. 9.9", and the 500 close up lenses changes it to 500mm/approx. 19.7".