Canon patent built in ND filter, If this patent it is commercialized, with minimal performance degradation of the lens, you will be able to use the filter anytime you wish .
Description, self-interpretation of the patent literature
- Patent Publication No. 2015-200805
- Published 2015.11.12
- Filing date 2014.4.9
- Canon patents
- On the surface of the transparent substrate made of synthetic resin, deposited the inorganic hard film of fine uneven periodic structure
- The refractive index changes toward the surface layer side from the transparent substrate side
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see more canon patents here Also take a look at – Canon Rumors
source - egami.co.jp
The build in ND filter was one of my wishes.