We didn't think the built in extender on the EF 200-400mm f/4L IS 1.4x was going to be a one off. Now a patent showing an optical formula for a new EF 400mm f/2.8L IS with a 2 stage built in extender has appeared. This would give the lens a focal range of 400mm, 560mm & 680mm.

Patent Publication No. 2016-191761 (Google Translated)

  • Published 2016.11.10
  • Filing date 2015.3.31
  • Focal length 392.57
  • F-number 2.90
  • Angle of view 3.15
  • Image height 21.64
  • Overall length of the lens 371.15
  • BF 44.00
  • The first state magnification 1.40
  • The second state magnification 1.70

We had heard previously that an extender was being tested in a new 800mm lens, but this may make more sense.

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