Canon has patented a super-telephoto prime lens in Japan. The new patent describes the EF 1000mm f/5.6 DO lens designed for Canon DSLRs with full-frame image sensors.

The EF 1000mm f/5.6 DO is a super-telephoto prime lens that was made by Canon. The optic will use an EF mount, and is compatible with the Canon EOS camera range.

It has a focal length of 1000mm and a constant aperture of f/5.6. From the DO designation we understand the optic will have diffractive optical feature.

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.
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http://www.dailycameranews.com/2016/06/canon-ef-1000mm-f5-6-lens-patent/