The !8-135 is crop mode only,....some people report that the 50f1.8 vignettes, well I find it usable(will test it again soon)
!8/55 usable from 24mm....55-300 useable...16/45 usable from 20/22ish....50-200mm usable from around 60mm
DA 40ltd useable..
And it can depend on the background too....if its blue sky vignetting will definitely be noticeable, other darker backgrounds and some slight vignetting is disguised
So,OP 2 out of 3 are ok.....the 55/300 is my most used lens on my K1
the" square crop mode, the DA lenses should work fine in that if can live that. I don't have one to test that out sadly
"
Very SAD!....But I tested all my Das that vignetted in FF mode and square mode eliminates some....and the square mode suits some photos(thanks Ricoh!)
---------- Post added 11-24-16 at 06:56 AM ----------
https://www.pentaxforums.com/forums/attachments/16-pentax-news-rumors/324333d...e-imgp1979.jpg
This is from K1, just a jpg resized...no PP....its from the 55-300 DA, and I may have had a 1.4x TC on too(cant recall)