I have the DA14mm, which is awesome and works beautifully on the D/DS
bodies. It was the only lens I bought with the camera, my "kit" lens.
If you really must have that wide a field of view for a 24x36mm
camera (I had a 15mm once and found I only very rarely used such an
ultrawide), and cannot find/afford the Pentax 15mm, people who have
tried both tell me the Tamron 14mm f/2.8 is the one to get.
Now, I'm going to have fun one of these days and fit my DA14mm to the
Pentax MX ... It will operate at minimum lens opening (f/22?) and
will make beautiful 24x24mm negatives. ;-)
Godfrey