Canon patent for EF 28-70mm F2.8 USM lens

• 14 years ago
• Categories: Canon
• Tags: Patents

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