Canon Files Patents for 45mm, 50mm, 60mm Prime Lenses

Egami, the Japanese Photography Blog has identified more patents filed by Canon, Japan. The patents refer to a number of lens designs : 50 mm f/1.4, 50 mm f/1.2, 45mm f/1.6, 60mm f/1.8, and describe an apochromatic design that aims to reduce chromatic aberration. You can read the original article in Japanese here.

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