According to latest Canon rumors, the company is developing more DO super telephoto lenses and the EF 800mm f/5.6 DO IS is one of the optical designs in the works.
“DO” designation stands for diffractive optical elements. Canon lenses which feature the diffractive optical (DO) are smaller and lighter compared to the same focal length lenses but the price becomes generally higher when the lenses have optical formual for DO.
Canon pioneered the development of the Diffractive Optics lens in the late 1990s and introduced the first Super Telephoto EF 400mm f/4 DO IS lens in 2001.
Canon EF 800mm f/5.6 DO IS Lens In Development
The current Canon EF 800mm f/5.6L IS USM telephoto prime lens is available for $12,999 at Amazon. A patent of the EF 800mm f/5.6 DO IS lens was spotted in December 2012.