nicolaiecostel: The aperture is not equivalent for anything, it's a fixed value. The DOF equivalence is a different thing.
People thought that if Pentax brings a cropped MF sensor to the market, in a oversized DSLR body, at 2.5-5 times cheaper than a Hassy, Phase One, they found the chicken with the golden eggs. They forgot that MF glass is MF glass expensive and all things MF come at a price.
So here you are, having just spent 5000-8500$ on a "bargain" MF Pentax, wanting to buy a modern, bespoke wide angle and realising you have to shell out 5 grand on either this zoom or that other wide angle they anounced, and that you're stuck with a cropped MF sensor that you can't remove from the camera and use in other cameras, that has 1/125 flash sync and you shoot on SD cards with limited teathering.
Why didn't they put a central shutter in the lens ? It would have been much more usefull than that OS they put in, seen the ISO and the fact that MF users shoot in controlled, stabilised environments.
Pentax has always made MF equipment for field use, which is why the system has the same type of user interface as on DSLR with smaller sensors, weather sealing, and stabilization.