I get a lot of questions about filters from students and other professionals. In the early days of shooting digital with a Sony PD150 I used a 1/4 BPM (black pro mist) to take the digital edge off of the video. Here is a comprehensive video testing out the current offerings of Tiffen in a formal test. Check it out.
Tiffen 4K Diffusion Test – 1080P from The Tiffen Company on Vimeo.