Egami found a patent filed by Canon for a 14mm f/2.8 lens with a new anti-reflective coating, Subwavelength Structure Coating. This method optimizes the refractive index and allows for a thinner anti-reflective film. Looks like Canon is working on a successor of the EF 14mm f/2.8L II USM lens. You can read the translated article here.
Patent specification (machine translated):
- Patent Publication No. 2013-47780
- 2013.3.7 Release Date
- Filing date 2011.7.26
- Example
- F = 14.3mm focal length
- Half angle ω = 56.6 °
- Fno. 2.89
- 14 images in 10 groups lens configuration
- Canon patent
- Antireflection film which is excellent in productivity and reflectance characteristics
- The refractive index of the substrate (original surface of the lens) is 1.65 to 2.20
- Consists of three layers, the ratio of the refractive index change with a three-layer
- The third layer
- Average roughness of less than 400nm pitch structure
- By continuously varying the ratio of the space-filling structure uneven, changing the refractive index
- After drying, the film is immersed in hot water and applied to the second layer solution (containing aluminum oxide) by spin coating, plate-like crystals deposited on the surface
- If spin coating of the wet process, excellent in productivity can be realized a uniform thickness
- Little change in the characteristics even if there is variation in thickness
