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
