Originally posted by jawats I've never used these before, but they looked interesting. Picked them up for $15 with shipping.
Congrats on a good buy! If one has any interest at all in close focusing, a set of auto tubes is worth having on hand.
Are yours made in Japan? In my experience, Japanese made K mount tubes are hard to find.
A few years ago I bought a set of Vemar automatic K tubes on ebay. I was amazed at their build quality compared to the (non auto) cheap, Chinese made K tubes I already owned.
There might be an issue though. Do your tubes have black mount surfaces? My Vemars have black mounts which are non-conductive. In order to get the tube / lens to stop down on my Pentax DSLRs, I had to sand off the black finish on the tube's mount where it meets the camera's contacts.