Originally posted by clackers In an age of post-processing, they're not a problem.
Yea. And it can be used for artistic effect - a lot of people
add vignetting digitally to emphasize the subject.
The DA 50mm f1.8 comes from the optical lineage of M 50mm f1.7, A 50mm f1.7, F and FA 50mm f1.7. Its a long line of FF lenses, with minor tweaks throughout the decades. The DA mostly has rounded aperture blade and better lens coatings than the old ones.
You can use the sample photo archive to look for photos taken with DA 50mm on K-1:
Pentax Camera & Lens Sample Photo Search Engine - PentaxForums.com SMC Pentax-DA 50mm F1.8 Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database
There is also a thread "DA lenses on Full frame" with user tests done to see which DA lenses are good, and just how good, on FF.
Think OP already made their decision, but posting in case anyone searches for this info sometime later