Egami spotted a patent filed by Canon. The patent describes diffractive optical (DO) lens of the EF 400 f/4 IS.
Canon lenses which feature the diffractive optical (DO) are smaller and lighter compared to the same focal length lenses but the price becomes generally higher when the lenses have optical formual for DO.
The current lens has been around since December, 2001 and is available for $4,200 at Amazon.
Canon Patent For EF 400mm f/4 IS DO Lens
- Patent Publication No. 2014-109700
- Publication date 2014.6.12
- Filing date 2012.12.3
- Example 1
- Focal length f = 392.00-381.59-332.99mm
- Half angle ω = 3.16-3.10-2.81 °
- Image height Y = 21.64mm
- The overall length of the lens 292.02mm
- BF 105.64mm