Canon Patent For 400mm f/4 DO Lens

Egami (translated) spotted another patent filed by Canon. It is for a 400mm f/4 lens with diffractive optical elements (to reduce flare).

Patent description (machine translated):

• Patent Publication No. 2013-64858
  • 2013.4.11 Release Date
  • Filing date 2011.9.16
• Example 1
  • Focal length f = 392.12mm
  • Fno. 4.12
  • Half angle of ω = 3.16 °
  • Image height Y = 21.64mm
  • 262.14mm length lens
  • BF 69.97mm
  • Two fluorite
• Materials and anomalous partial dispersion DOE to use, reduce the chromatic aberration
• Refractive power of the diffractive surface
  • Strong, but can reduce the chromatic aberration of the element itself, flare increases
  • The weaker, other optical element DOE play a role
• Refractive optical unit
  • DOE anomalous partial dispersion and bonding materials
  • DOE aspherical surface on the opposite side of the
• Vibration control
• Inner Focus

[via Egami]