being mindful of various mis focusing complaints of the K5 in low light, I did a quick and dirty test on mine with a lately acquired 100mm macro. My target will re recognized as a name tag on the side of a Pentax lens sitting on a table top, and I sat in a chair beside the table putting me about arm's length away and set about a 30 degree angle to the tag.
Lighting was so dark that I couldn't read the tag with the naked eye. The exposure called for 1/10th of a second, ISO 12800, and f/2.8. I took both photos hand held with single point focusing, and single point exposure, and kept my fingers out of the focus assist light path.
Lighting was a single incandescant bare bulb overhead and a bit to the back shadowing the bottom of the tag a little more.
In one photo I put the red indicator on the top lines of text and in the other on the bottom lines of text. You won't have a problem telling which is which.
My conclusion: at least with my K5 and my recently acquired FA 100 macro I'm getting a reasonable exposure, and it focuses where I point it even with crummy lighting