I recently read somewhere that used copies of the Zeiss ZK 50mm lenses are almost never available for sale anywhere. While this statement is true, those of you wanting to use a high quality Zeiss 50mm lens on the K1 have another option!
Zeiss made a "ZS" version which is in the M42 mount. Get yourself a M42 to K adapter and you can use a Zeiss ZS lens on your Pentax digital cameras.
I just happened to find such a lens (
RARE Carl Zeiss Planar 50 1 4 ZS for M42 72188 T1974 | eBay ) on Ebay today for only $460 USD from a reputable seller!
So, if you don't mind using the green button on your Pentax camera, you can regularly find nice Zeiss M42 mount lenses on EBay.
P.S. This is not my lens, nor do I have any type of relationship with this Ebay seller.