Not sure why Canon filed that patent two years ago, since the old Canon EF 28-70mm f/2.8 L USM lens was replaced by the EF 24-70mm f/2.8L USM.
The details:
- Patent Publication No. 2010-145831
- published 2010/07/01
- filled 2008/12/19
- Embodiment 3
- focus distance f=28.7-68.00mm
- Fno=2.92
- angle of view 74.02-35.30
- image circle 43.28mm
- lens length 177.91-168.98mm
- back focus 46.71-75.33mm
- Zooming, there are few changes of distortion
- Retrofocus optical in wide angle
- Tele-photo optical in tele-photo
- short full length
- Distortion is big in wide angle
- astigmatism turns worse if it use the aspherical where the quantity is big
- problem solving by a certain a lens was arranged in symmetry, and denying the distortion
- Use aspherical
- improve distortion
- Because it is not necessary to make non-spherical surface quantity big, the astigmatism does not turn worse
