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A patent showing an ND filter to increase dynamic range for only half the field of view.
In English (Thanks Keith):
Introducing a neutral density filter for only half the field, you get differing amounts of light to AF pixels that are split on the same axis as the filter. This would increase the differential output of the sub-pixel pair as you pass through sharp focus.
Patent Publication No. 2015-87401 (Google Translated)
- Published 2015.5.7
- Filing date 2013.10.28
- Dual Pixel AF
- And set up a half-ND filter at the pupil position of the lens
- Half ND filter can be switched