Easily the best optics of all the sigma 400 models.This is the superior 77mm filter size canon ef version  one of two models made,both have the black rubber zen finish and  both have the same optical quality, this is the non hsm motor model and has slower autofocusing.
Autofocus is retained at f5.6
This lens only works at f5.6 with canon digital cameras on manual or av mode but at any aperture on film 
super clean optics great for age no fungus or problems  with only surface matt marks to the surrounding rubber armour especially on the built in hood
 very high quality famous for its lack of colour artifacts  and sharpness and has the best optics by miles of all the  other sigma  400 long teles
Complete with built in hood tripod bracket and both caps 
no case sent next day delivery in big box covered in bubble wrap

http://www.pentaxforums.com/userreviews/sigma-400mm-f5-6-apo.html

The Sigma AF 400mm f / 5.6 lens SLR cameras is a macro lens. Mostly, this Sigma lens is used for in sports and wildlife photography. This SLR lens, like other lenses of this class, is very heavy (about 1.4 kilograms) and has a size of 256x91 mm. The optical construction for this Sigma is made up of 10 elements in 7 groups with 2 SLD elements. In the aperture mechanism, the lens 9 provides diaphragm flaps. According to the manufacturer's specifications, the Sigma AF 400mm f / 5.6 lens is a macro lens. In fact, it is not a typical floating system for narrow focus correction, as is normally the case with macro lenses. Nevertheless, the Sigma can offer a maximum object magnification of 1: 3 at a minimum distance of 1.6 m. The filter for this lens is 77mm. The Sigma is an IF (internal alignment) lens, which keeps the size constant regardless of the focus setting and the front of the SLR lens can not be moved or rotated. The AF (autofocus) is very reliable with this lens and full-time manual control of the AF in one shot mode is possible at any time. In addition to a built-in barrel hood, this Sigma lens also has a tripod mount on the lower side of the lens.