I recently bought a Pentax K-50 in a set with two lenses (18-55 & 50-200) as well as a 50mm fixed focal length lens. The camera is great but I am extremly disappointed in the lenses. Two out of the three lenses show significant chromatic abberations in the extreme aperture settings. See the picture below for a 1:1 crop of some pictures taken with the 50mm f/1.8 lens with a tripod, iso 100, without shake reduction or any CA correction.
Do I have to live with this kind of abberation? (Which would basically mean that I will only take pictures with f/3.2 or larger...) Are the lenses broken? Several reviews call the abberation "negligible" (as it should be with a 50mm fixed focal length, eg. http://www.photoreview.com.au/reviews/lenses/aps-c/smc-pentax-da-50mm-f-1.8-lens) but certainly they would not call this negligible?
EDIT: Note, that this toothbrush was in the center of the picture and that several tests photoreview.com, ephotozine.com estimate the abberation to be clearly below 1 pixel while my picture shows more than 17 pixels of abberation with f/1.8. So what is going on here?
EDIT2: As the answers correctly noticed, the toothbrush was not in the center of focus. Apparently this lens has a distinct tendency towards green for objects that are behind the plane of focus and towards red for object before it.
I am still kind of disappointed in the lens - and especially that no review mentioned this. I am pretty sure my old Minolta lenses did not have this effect. At least I now (somewhat) understand where it comes from.