K-bayonet Pentax

FAQ Section 3: Pentax bayonet mount equipment

Q: Can I fit M42 lenses to any Pentax K-bayonet camera?
A: Yes, via the Pentax K-mount Adapter. The only limitation is you have to meter at taking aperture (Stop-Down metering), also in case of full-aperture SMC Takumar lenses. This is because full-aperture couplings of K-bayonet and screw mount are different and cannot match and work.
Also, only stick to original Asahi K-mount adapters, since most third party adapters are not machined to proper tolerance and can give problems.

Q: Has Pentax ever manufactured any f/1.4 35mm lens?
A: A SMC Pentax-M 1.4/35mm lens was announced several times by Pentax around 1980 and was also present in sales catalogs for a short while. In spite of that, according to a source from Asahi Opt. Co. Ltd. only 6pcs of that lens were manufactured before production was stopped. None of them was put on sale. The reason because Pentax changed their mind about such an interesting lens is unknown. Here is an official picture of the SMC Pentax-M 1.4/35mm lens.