Currently there are 8 native Telephoto Prime lenses for Sigma SD1 Merrill and all of these lenses are autofocus (AF) type.
Sigma SD1 Merrill doesn't have a sensor based image stabilization system but 1 of these Telephoto Prime lenses features optical image stabilization.
Since Sigma SD1 Merrill has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 4 Telephoto Prime lenses with Weather Sealings.