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Another super-telephoto diffractive optic patent
This patent deals with joining an aspherical element with a DO element group.
In this patent is listed embodiments for a 300 2.8 IS DO and another 400 4.0 IS DO.
Canon continues to work on improving the diffractive optical super telephotos, and maybe just maybe we'll see a 300mm DO similar to what Nikon has come out with.
Read more US Patent Application 20170168269