How do I make an airbrush?(I don't mean the airbrush build-up setting)

What exactly I'm looking for is no edge at all, not even a soft one, and a very gradual change over a large area. I have like 100 different tip shapes and maybe 4 of them look like a potential airbrushes, but I can't make any of them behave the way I want. I have played with spacing and hardness. Hardness is at 0. I don't really know what else I can do.

I'm coming to PS from SAI and CSP where it's braindead easy to make this. Both actually have "Airbrush" tools. It's super useful and I find it basically a necessity, yet I can't figure out how to do it in PS. The brush I'm trying to make seems like such a necessity for even things like photo editing that I can't believe it doesn't come standard with the software. Maybe it does and I just don't see it?