Anti-reflection coating, optical member, exchange lens unit and imaging device

1. An anti-reflection coating comprising first to seventh layers formed on a substrate in this order, said first layer being an alumina-based layer, said seventh layer being a porous, silica-based layer, and in a wavelength range of 400-700 nm,

said substrate having a refractive index of 1.60-1.95,

said first layer having an optical thickness of 37.5-112.5 nm,

said second layer having a refractive index of 1.95-2.25 and an optical thickness of 35.5-60.0 nm,

said third layer having a refractive index of 1.35-1.50 and an optical thickness of 24.5-41.5 nm,

said fourth layer having a refractive index of 1.95-2.25 and an optical thickness of 210.5-250.0 nm,

said fifth layer having a refractive index of 1.35-1.50 and an optical thickness of 12.5-32.5 nm,

said sixth layer having a refractive index of 1.95-2.25 and an optical thickness of 27.5-45.0 nm, and

said seventh layer having an optical thickness of 108.0-138.0 nm.

2. The anti-reflection coating according to claim 1 , wherein said second layer, said fourth layer and said sixth layer are made of at least one material selected from the group consisting of Ta 2 O 5 , ZrO 2 , HfO 2 , CeO 2 , SnO 2 , In 2 O 3 and ZnO, and said third layer and said fifth layer are made of MgF 2 and/or SiO 2 .

3. The anti-reflection coating according to claim 1 , wherein said first layer has a refractive index of 1.59-1.69.

4. The anti-reflection coating according to claim 1 , wherein said seventh layer having a refractive index of 1.25-1.30.

5. The anti-reflection coating according to claim 1 , which has reflectance of 0.5% or less to incident light at 0° in a wavelength range of 450-600 nm, and reflectance of 1.0% or less to incident light at 30° in a wavelength range of 400-650 nm.

6. The anti-reflection coating according to claim 1 , wherein said seventh layer is a silica aerogel layer.

7. The anti-reflection coating according to claim 1 , wherein a fluororesin layer as thick as 0.4-100 nm having water repellency or water/oil repellency is formed on said seventh layer.

8. The anti-reflection coating according to claim 1 , wherein said seventh layer is formed by a sol-gel method.

9. An optical member having the anti-reflection coating recited in claim 1 .

10. An exchange lens unit comprising the optical member recited in claim 9 .

11. An imaging device comprising the optical member recited in claim 9 .

12. An anti-reflection coating comprising first to seventh layers formed on a substrate in this order, said first layer being an alumina-based layer, said seventh layer being a porous, silica-based layer, and in a wavelength range of 400-700 nm,

said substrate having a refractive index of 1.50-1.70,

said first layer having an optical thickness of 24.5-200.0 nm,

said second layer having a refractive index of 1.93-2.25 and an optical thickness of 24.5-50.5 nm,

said third layer having a refractive index of 1.33-1.50 and an optical thickness of 14.0-30.0 nm,

said fourth layer having a refractive index of 2.00-2.16 and an optical thickness of 131.5-200.5 nm,

said fifth layer having a refractive index of 1.33-1.50 and an optical thickness of 20.0-31.5 nm,

said sixth layer having a refractive index of 2.04-2.17 and an optical thickness of 50.0-62.5 nm, and

said seventh layer having a refractive index of 1.23-1.32 and an optical thickness of 122.5-142.5 nm.

13. The anti-reflection coating according to claim 12 , wherein said second layer, said fourth layer and said sixth layer are made of at least one material selected from the group consisting of Ta 2 O 5 , ZrO 2 , HfO 2 , CeO 2 , SnO 2 , In 2 O 3 and ZnO, and said third layer and said fifth layer are made of MgF 2 and/or SiO 2 .

14. The anti-reflection coating according to claim 12 , wherein said first layer has a refractive index of 1.57-1.72.

15. The anti-reflection coating according to claim 12 , which has reflectance of 0.3% or less to incident light at 0° in a wavelength range of 450-600 nm.

16. The anti-reflection coating according to claim 12 , wherein said seventh layer is a silica aerogel layer.

17. The anti-reflection coating according to claim 12 , wherein a fluororesin layer as thick as 0.4-100 nm having water repellency or water/oil repellency is formed on said seventh layer.

18. The anti-reflection coating according to claim 12 , wherein said seventh layer is formed by a sol-gel method.

19. An optical member having the anti-reflection coating recited in claim 12 .

20. An exchange lens unit comprising the optical member recited in claim 19 .

21. An imaging device comprising the optical member recited in claim 19 .