Canon has just filed a new patent for the Canon EF 400mm f2.8L IS lens with two stage built in extender. This will give the lens a focal range of 400mm, 1.4x (560mm) & 1.7x (680mm).
Detail translated by Google:
- Patent Publication No. 2016-191761
- Published 2016.11.10
- Filing date 2015.3.31
- Example
- 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
Source: EGAMI