This thread is mostly for me, but I figured that I'd post it instead of just making my own notes as it might be of casual interest to someone. Read at your own peril - this will likely fall down every rabbit-hole available.
Still with me? Ok, to catch up to where I am, watch and study these videos....
If you're not lusting after the $40,000 Zeiss Master Anamorphic after watching the first one then go watch them all again before proceed
Well, there is no shortage of them, that I can tell.
There is Tiffen Black Diffusion/FX and Schneider Radiant Frost, which (according to David Mullen) soften the image with minimal halation added.
Not to mention a whole lot of Satins (Black Satin!), etc.
Some good read here: https://www.thebroadcastbridge.com/content/entry/4071/its-time-sharpen-your-diffusion
And last, but not least, a handy diagram from Tiffen:
Someone already na