It is a very long process to clean the Aperture Oil in a Pentax Takumar 28mm 3.5 SMC but it is well worth it as this is a great little lens and are easy to find. Just make sure you have a spanner before you start repairing the lens.
This unique & sharp Helios 58mm f/2 44-2 lens has a nice and narrow mount with the rear element sticking out. This feature makes the lens great for Lens Whacking or Free Lensing. For normal, still photography this M42 lens does a good job and has the 58mm focal length I prefer over a 50mm. This lens is so well built it feels like you’re holding a hefty machine that will take a beating and keep on working.
This Pentax Super Takumar 105mm f/2.8 is a decent lens stopped down a wee bit and you can’t go wrong with it if you find a good deal. Being a M42 mount you can use this lens on some Digital camera bodies with an Ebay M42 Adapter. Also split focus screens from Ebay make focusing a lot easier!
This Chinon 55mm f/1.4 Auto is fantastic mechanically and optically. There is not a whole lot of talk about this lens and probably for one reason. The rear element sticks out a fair bit and can hit the mirror on certain cameras if your using it on a DSLR with an adapter. However moving the focus away from infinity makes enough room to shoot or with the mirror up.
The Pentax Super Takumar 50mm f/1.4 Asahi is another amazing example of a really well built M42 Manual Focus lens which Pentax is famous for. If you don’t mind manual focus then this little lens is great for even today’s digital cameras with M42 adapters.