My M 50mm f1.7 is probably on my K-5 90% of the time. I spend a lot of time making portraits of interesting small plants, which this lens excels at since it's quite acceptably sharp wide open, such as this one:
But my
real obsession is making portraits of trees. These being a bit larger than wildflowers, it's tough to get similar relative DOF in a single frame, working at a greater distance- but the M 50mm f1.7 remains the perfect piece of glass for taking a whole bunch of frames wide open closer in and stitching them to simulate a larger capture medium.
On that note, this nice nifty fifty even does a stand-up job as a wide-angle landscape lens.
I periodically look at wider-angle lenses in the marketplace and always talk myself out of them on the basis of how well this lens does for me. The only improvements I can imagine would be rounded aperture blades and a slightly closer minimum focus distance. In every other way, I am of the opinion that this little lens is as close as possible to perfection.
This is for the best, since the stitched images really don't quite look right on a small screen or as small-to-medium sized prints, and I've got to put that money into printing instead of LBA!