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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.