This is the longest telephoto lens among Canon's lineup, and a terrific choice for any long-distance application-outdoor sports, wildlife, news photojournalism, and so on. It's actually lighter than Canon's EF 600mm f/4L IS lens, weighing just under 10 lbs. It uses a refined optical design, with two fluorite lens elements, one UD element, and one Super-UD-glass element, for outstanding correction of color fringing and superb contrast and sharpness. This super-telephoto lens uses magnesium-alloy barrel construction to enhance its light weight, and has weather-resistant gaskets throughout for use in harsh conditions

• Focal Length & Maximum : Aperture 800mm f/5.6
• Lens Construction : 18 elements in 14 groups
• Diagonal Angle of View : 3?? 5' (with full-frame sensor camera)
• Focus Adjustment : Ring-type Ultrasonic Motor, with inner focus system; mechanical manual focus
• Closest Focusing Distance : 19.7 ft./6.0m (maximum close-up magnification: 0.14x)
• Filter Size : 52mm (Drop-in Gelatin Filter Holder)