Pentax-A 100mm f/2.8 SMC Macro
There are some extremely amazing lenses out there and this Pentax-A 100mm f/2.8 SMC Macro is a prime example of mechanical and optical perfection. However this is a hard to find lens and still costs just as much as a newer auto focus 100mm macro lens even today. For perfect focus I would check Ebay to see if you can get a split focus screen for your body.