Originally posted by Canada_Rockies Using an A or later lens, pressing the green button by the shutter sets the exposure to the program line. Earlier lenses will set the shutter speed to the Av exposure for the mounted lens wide open.
RMabo had it most accurately, the green button on the K10D is programmable for how you want it to function, it can follow a program line, or be set like shutter priority or like apature priority.
The first will be based upon lens data, the second , if you select it will be useable with automatic lenses and set apature assuming you want to keep the shutter speed where it is, the third for non automatic (no A setting on the apature rring) lenses, or if you wish to pick depth of field specifically, and will set the shutter for the apature. I have proposed to pentax to give a 4th setting, specifically to take a reading and show only over/under exposure but not change anything. No response yet