Dear Pengbai, I wanted to send a private message but i can't do it yet because i'm a new member. I saw you sold some Zeiss ZS and ZK lenses in the past. Is there a difference in quality/use when mounted on a Pentax digital camera (K-1)? I can buy a ZS version in my country and the Ebay ZK versions are expensive. So the ZS might be a good option if the quality with a m42 adapter is the same. ...