As you know most high end Cinema Prime lenses don't offer threads for screw on filters. Whether it be a BlackMagic Design Production 4K, URSA, URSA MINI, or even a RED, one thing about working with with cameras that lacks built in ND filters, is that you may have to work with drop in filters and heavy matteboxes. So we decided to come up with a cheap DIY 3D printed lens clamp of our own to hold filters in place.
Since we're working with the XEEN Cinema Primes that have a 114mm diameter we needed a filter that was oversized, so that it wouldn't obstruct a view on wide angle lenses. We found the most inexpensive and large filters were 145mm from the FotoDiox Wonderpana System. They also offer many different stops of ND and CPL Polarizers for more options to control your image.
The 114mm is a common size shared by Canon CN-E Cinema Lenses and even Zeiss CP.2 Cinema Lenses (and many others), so this little adapter will work on those lenses as well. The design can also be modified to clamp other filters to Ultra Wide or Fisheye lenses that can't accept front threaded filters. (I need to make one for my Rokinon Fisheye). If you're wondering how it actually clamps, there's a small 2" slit right that separates the clamp are from the filter holder. This allows the clamp to compress a few millimeters - enough to clamp very tightly.
Anyhow it's an idea I wanted to share as I'm sure there are many instances in which this lightweight filter clamp holder could be very advantageous. Here's some additional photos of our 3D Printed Filter Clamp Holder.
For normal lenses with filter threads, I suggest using these simple Swing Away ND Filter Holders.
Swing Away Lens Filter Holder for ND Filters CPL