Hi kye: I still need to ask you what's a "P4k" ? [Is it a Panasonic 4k camera, like a Lumix G7? I know that the G7 has a four thirds/ 17.3x13mm sensor, and probably one can still shoot on a 8mm lens, with vignette effect]
My clear preference was for an action camera, too - but I think I need to put it on hold for the moment. I also considered buying a cheaper action cam (e.g. an Akaso), and to grind away the metal body & try to fit the D-mount lenses, but honestly the point is to get some good quality, otherwise looks like wasted time.
Finally, in one of my pure idealist moments, I was thinking to try to film on the 8mm vintage cameras that I'm currently try to purchase
Thanks again for your pieces of advice,
I got me two sets of D-Mounts. Three Kern Paillards and two Yashicas. They cost me €12 + €6 + shipping for all of them and included two cameras as rear caps.
If someone wonders about the specs compared to a modern Canon or Panasonic equivalent they are smaller, cheaper and better built with loads of character. So better speced indeed
Here is a sample of the Kern 13mm f1.8
Here the Kern and Yashica 13mm goes head to head.