Fotodiox released something really cool recently. A 10 stop variable ND filter built into a Canon to E-mount lens adapter.
Canon EF – Sony E-Mount Lens Adapter
I often use NDs for landscape photography and find it to be a hassle always switching and owning different NDs for my different lenses since they all have different filter sizes.
And if you've ever used a variable ND filter on an ultra wide lens you'll know that they just don't work well when mounted to the front element. The same applies to polarizes which is how variable ND filters work. But when mounted to the back it all works great.
Everything seems like peaches and creme with this new lens mount adapter except one thing. You can't electronically control your aperture. So I can't really see it being of much use on Canon lenses.
All your great Canon landscape lenses like the 16-35mm f2.8 II the 16-35mm f4 or the 17mm TS lens will have have massive limitations by not being able to control the aperture. Which seems weird because they are marketing this thing with Canon lenses.
However, if you have manual lenses like Samyang or Zeiss with a EF mount then you'll be good to go. It will be fun to finally give ND love to the Samyang 14mm f2.8 lens which has no front filter threads.
I'll be adding this to the Sony A7, A7r, and A7s recommended gear page where I keep a list of some cool accessories for these cameras.