>>3630892Those are the "Limited" primes. They were designed with some weird guidelines with limitations to size, elements used etc...
Basically they solved optical issues like distortion and CA etc. with the weird focal lengths instead of increasing the number of corrective elements
>>3630827There are plenty of good lenses for Pentax, look into the DA line, the DA Limiteds for example are pretty good lenses, the DA* telephotos and zooms are superb apart from the DA* 16-50, it is weird, has horrible CA if you do just a single mistake, has superb image quality if you get it right, definitely not for beginners. My DA 16-45 plastic fantastic was much more forgiving.
The DA 35 and 50 primes are cheap as salt and have pretty good IQ.
Tamron lenses in K-mount are excellent apart from the superzooms, but you should always avoid those things, no matter what brand you use. The Tamron 70-200/2.8 is cheap and very nice, the 90/2.8 macro as well. The 17-50 also has very good IQ.
I suggest you go on the Pentax Forums lens database and check it out for yourself.
