See my Pentax K1 wish list at B&H Photo.
The Pentax 43mm f/1.9 is a “pancake” lens with 7 elements in 6 groups. The expectations should be clear: the 43/1.9 is almost certainly designed for bokeh qualities and compactness. It almost certainly has field curvature and some measure of focus shift. Thus this target is going to be about as non-ideal as it gets for the 43mm f/1.9.
Here is what Pentax has to claim:
The ultra-compact smc PENTAX -FA 43mm F1.9 Limited lens offers exceptional high-contrast, high-resolution optics with minimal aberrations. It features the acclaimed smc multi-layer coating to lower surface reflection, reduce ultraviolet rays, and deliver clear, high-contrast images.
Real-world results leave one’s mouth agape at reconciling the above:
Includes images up to 28 megapixels and large crops, all from f/1.9 through f/13.
The entire series is shot in SuperRes pixel shift mode on the Pentax K1.