WHY would you purchase a FULL FRAME Pentax? (In point format)

James O'Neill wrote:

Actually it will make a DOF difference. The circle of confusion will be the same absolute size whether you have cropped the edges off the image or not. But the size of CofC you can have and still appear in focus increases as the image area increases, so you will get more DoF with the same focal length on a a biger sensor.

Since CofC size varies with the square of focal length, when you have a 2/3 size sensor use 2/3 the focal length, and CofC is 4/9 the size. You need to reduce it to 6/9s the size (2/3) to get the same apparent focus. Hence smaller frame, more DoF for the same angle of view and apperture.