The only way to achieve prime focus on the P. S. T. with a DSLR or Mirrorless camera is to attach the lens assembly from a 2X barlow to the T-ring adapter (extension tubes don't work). It took me a while to figure this out!
This turns the P. S. T. into a 960mm, f24, Hydrogen-alpha telephoto lens!
BTW, if you screw the lens assembly from a 2x barlow directly to an eyepiece, it becomes a 1.5X barlow! So basically, if you have a 2x barlow with a removable lens, you can triple your eyepiece collection!
All of this is good information to have if you're at a party.

Canon EOS M10, Coronado P. S. T.
Prime focus at 19X
1/50s, ISO800