Canon Files Patent For New Primes (45mm, 50mm, 60mm)

Egami spotted another patent filed by Canon. The patent refers to s 50 mm F1.4 , 50 mm F1.2 , 45mm F1.6 and 60 mm F1.8 lenses, and describes an apochromatic design that aims to reduce chromatic aberration.

Patent description (machine translated):

• Patent Publication No. 2013-57802
  • 2013.3.28 Release Date
  • 2011.9.8 filing date
• Example
  

  Example

  	Focal length	Fno.	Angle of view	Focus
  One	51.7	1.45	45.4	Floating rear focusing +
  Two	51.7	1.45	45.4	Fed whole
  Three	51.7	1.25	45.4	Floating rear focusing +
  Four	51.7	1.25	45.4	Fed whole
  Five	45.0	1.6	51.4	Fed whole
  Six	60.0	1.85	39.7	Fed whole

• In many large-diameter Gaussian secondary spectrum of axial chromatic aberration
  • This problem occurs when using glass and others with the same Abbe number, a lens that is different partial dispersion ratio
  • When used in a positive lens lanthanum flint glass small partial dispersion ratio
  • When used in a negative lens of flint glass titanium large partial dispersion ratio
• Canon patent
  • Using a lens with a partial dispersion ratio appropriate correcting the axial chromatic aberration secondary spectrum
  • The concave lens surface adjacent to the aperture, coma aberration correction, the sagittal flare

[via egami]