I recently bought myself a K10D. I was online searching for a cable release because my "Pentax Cable Switch F" from my zx-50 doesn't fit the K10.
During my search, I came across this thread, " DIY: Make a Cable Release for your K10D", in the Pentax forums and it got me thinking about how I could use my "F" release on both cameras even though the old plug is a dedicated shape for Pentax while the new plug is simply a 2.5mm plug.
A/ -first -I found a 2.5mm plug in one of my "spare stuff" boxes. This is just like a "regular" earphone plug (3.5mm) but smaller.
(I had already cut the other end off, I think it was for the rca plugs.)
B/-second -I dug up a piece of wire that fits the holes in the "F" release plug.
I used a piece of electrical wire. The wire needs to be solid, not the braided kind.
C/- third-I stripped the wire on the 2.5mm plug and ended up with 1 red wire, 1 white wire, and a silver (without the insulation) wire There were actually 2 silver wires which I twisted together as a "common" or "ground" wire.
D-fourth-I did some testing to find out which wire goes where. I cut 3 pieces of wire and fit them in the end of the "F" plug then touched the wire from the 2.5mm plug to these until I had the right combination to make it work the way it should.
I ended up with my white in the middle, the red on the on the square side, and the silver on the beveled side of the plug. This can be seen in the photo where the "Pentax" on the plug is upside right.
E/-fifth-I had a couple electric wire crimp connectors that I used to connect the solid wire to the braided wire.
F/-sixth-I used a little epoxy to hold the whole thing together and wrapped it in electric tape for until the glue dried. After the epoxy set, I pulled off the electric tape and seperated the new "plug" from the F plug.(carefully, but I still left scratches)
I used epoxy because when it dries it doesn't conduct electricity.

Sooo, now I have a cable switch for both of my cameras and also (seperately), a mechanical cable for my Spotty.

footnotes: *If you try this at home, this switch works whether my "plug" has the red wire on one side or the other, but after completion, I keep it oriented the way it was when I made it.
*Whatever wire you use may or may not be the same colors as mine but will probably work just the same.
*Also, using a scavenged plug, I don't know which ring on the 2.5mm plug relates to which wire. A new plug (radioshack?) would allow this question to be answered.

[Steve Beswick]

First, are you using a M series lens on a ZX-50? How are you doing so without massive exposure errors?

Second, why didn't you just wire a pair of switches to the cable with the 2.5mm plug, and leave the "Cable Switch F" out of the equation?

[jonhock]

#1-The reason the M is on the zx-50 is because it was already on the kitchen table on acounta me selling it (the lens, not the camera) when I decided to post a couple "show me" photos of the cable on both cameras. I have however, used it and never noticed a problem. Until you just asked me about it, I had never wondered about it. I just now looked around a little and found out that the shutter shouldn't even fire with this combination! I didn't know that. My zx didn't know that either. I just started a thread in the beginners forum to try to get some more input/answers.

#2- I didn't wanna. I was looking at the homade switches and rather than make one, I figured I'd just plug the 2.5 cord into the F switch. I have operational autofocus prior to shutter release and can lock it open when in bulb mode on either camera and I didn't buy anything extra to do it.

[Steve Beswick]

For the sake of clarity, I was not trying to criticize, I was just curious.

Edit: I'm surprised you are having so much luck with the M series lens on the ZX-50. It shouldn't meter properly at all except for wide open.

[jonhock]

I guess I need to use more
I didn't take it as critissixm (cripes, i can't even spell it!) The question about the lens did get me to wondering. I was surprised at what I found when I checked into it. Thanks