Originally posted by Edward_K What modifications can be made to make it lock so I don't have to hold the lenses in?
Place your C/Y lens face-down in front of you. Looking at the base, you will see three bayonet flags. One flag has a notch in it. That notch is near the "leading edge" of the flag. The problem is that the flags are too thick to fit under the PK mount lugs. The solution is to taper the undersides of those flags so that they DO fit under the lugs.
Definitions: UNDERSIDE OF FLAG: the side of the flag towards the front of the lens.
LEADING EDGE: the edge of a bayonet flag that first makes contact with a mount lug.
TAPER: Grind away the flag underside so its leading edge is wedge-shaped.
An Olympus OM-mount lens is similar; all three flags must be tapered. With a C/Y lens, don't taper the flag with the notch, just the other two. I use a Dremel metal-cutting disc to (CAREFULLY!) cut a slope that extends back about 8mm from the leading edge of each flag. The modified lens will now force-fit onto the PK mount -- good enough for careful use, but not locked on. A modded OM or C/Y lens should still be usable on its native mount.
Now comes the part I haven't done yet, but I should, on all the OM, C/Y and AI (Nikon) lenses I've modded. Force-fit the lens onto the PK mount. Note where the camera's locking pin touches the lens. Mark that point. Dismount the lens. With the Dremel, cut a notch in the lens base that will accommodate the locking pin -- about 2mm wide and deep, and 5mm long.
I didn't just devise this method out of thin air. I bought several cheap basic PK macro tube sets (US$7 shipped from Hong Kong). These have modular screw-on extension sections, and male and female camera-lens mount pieces. The female mount piece is an excellent test-bed for mount conversions. Loading a lens onto it is like looking at the lens from inside the camera -- you can easily see where bayonet flags and mount lugs do and don't interact.
Before modding a lens that means anything to you, I
strongly recommend that you buy such tubes, and practice on a junk lens. This is really simple surgery, but it's still not for the faint-hearted. I am no machinist, oh no no. My mechanical abilities peaked when I was building slot-cars many decades ago, and I didn't even have a Dremel then. But proceed carefully and you should have no trouble. Be sure to air-bomb all metal dust away after cutting and grinding. Good luck!