By adding Sigma’s dedicated APO EX Tele Converter 1.4x and 2x, you can use this lens as a 1120mm F8 MF, or a 1600mm F11 MF lens respectively.
Lens Construction
13 Elements in 10 Groups
[800mm F5.6 EX APO HSM] SIGMA (H), NIKON ( H D),CANON (H)[800mm F5.6 EX APO] MINOLTA,PENTAX