Originally posted by Alaska Pentaxian ...someone was using a Canon and the mirror struck the rear element of the lens...
I will point out that this is an issue specific to Canon cameras not Pentax cameras. There aren't any issues with this camera/lens combination because the K mount has
exactly the same flange focal distance as the 42mm screw mount did. Canon DSLR cameras have a shorter flange distance* and this causes mirrors to scrape on lenses designed for longer flange focal distances. I have used the Takumar 50mm f/1.4 8 element version on my K10D without issue.
*Flange focal distance - the distance between the rear element and the sensor when the lens is focused at infinity - on Canon EOS cameras this distance is = 44mm. Pentax uses 45.46mm