Wanted to use a Super Takumar 35/3.5 on a K-5. Bought an M42 adapter from a vendor in China via eBay. I thought it did not focus to infinity and needed adjustment. This thread is about that:
https://www.pentaxforums.com/forums/general-technical-troubleshooting/161673-...ity-k-5-a.html
Never got past faceplate removal. Bought the Pentax adapter. You can see the difference in thickness. The Pentax adapter is the narrow one:
The difference is about 0.5 mm.
However, the Chinese adapter came with a handy grip tool; Pentax does not include this simple piece of metal. Despite reports about difficulty removing an M42 adapter from a camera mount, it has been easy with the Pentax adapter: unscrew lens, insert prongs of grip tool into slots on adapter, hold down lens release button, and gently turn counter-clockwise. The adapter will barely turn, but it is now loose; set aside tool and with fingers rotate and remove the adapter.
My guess is that the lens does focus to infinity. The Takumar is just not as sharp as one becomes used to with an FA 35/2. The Takumar is still somewhat soft at f/5.6, but not seriously so at f/8. Intended focus here was the metal barrier:
Water gate