Glad I kept the 6 prime Super Taks, I bought while stationed in Vietnam. Kept putting off buying a digital body, waiting for full frame Pentax prices to drop. Well, couldn't wait any longer, one only lives so long...
Just got new K-70, and 3 Pentax brand M42 adaptors. Using Av, after making other settings. So, don't need green button. Must disable auto ISO also. When camera turned on, must verify focal length.
Didn't have time to read through all these threads, so if I'm repeating anyone else here, excuse me:
Now, I just focus at wide open, turn aperture ring until I see shutter speed I want in viewfinder, and snap away. If viewfinder is too dark, I increase ISO, (400 is what I seem to use most), shooting wild critters @ 1/500, depending on depth of field I want.
Decided to put adapters on lenses instead of camera for faster lens swap. After looking at new lenses prices, the $80 for an adapter is still a bargain. I had read the real Pentax adapters were not available, any longer however, B&H shows they have them.
You have to remove the tiny Phillips screw and spring from it to use on lens. I had problem with this with tiny jeweler's screwdriver, could not get enough torque to start screw moving. So, clamped small needle nose vice grip pliers to driver shank, made sure tip was hard set into screw and turned it out. You have to have correct size Phillips bit, it is tiny. If driver is not exactly right size, you will strip the head and then a have a real problem. If it still does not want to move, I suggest soaking it in Kroil, ( which I also did on one ), overnight, but make darn sure you get all Kroil off with a, no residue solvent, afterwards. That oil will migrate into camera or lens if not totally removed. I used a toothpick soaked in Kroil, then placed tip of it against back of screw, letting oil migrate into threads.
Other little problem is, after lens is attached and removed, the adapter is really hard to get off lens. I could not do it with my fingers as the edges on it are kind of sharp. Tried with leather gloves and just got it off, but then tried a sheet of rubber 1/8" thick cut to about a 3" square, pressed against adapter and twist, comes off fairly easy. I have 3 adapters and 6 lenses, so will have to swap adapter now and then. And, this way, if I get some auto lenses, don't have to go through the real pain of removing adapter from the body, trying to compress that little spring with a tool and turning adapter at same time.
Super Taks I have; f4-17mm fisheye, f3.5-24mm, f1.4-50mm, f4-50mm Macro, f2.5-135mm, f4-300mm. All bought new in 1968.