There seems to be two main lens options for rectilinear ultra-wide (weitwinkel) angle (so no fisheye) in the micro four-thirds galaxy: Panasonic 7-14mm and Olympus 9-18mm.
Which one is best?
In case the answers are "it dependsish", I would look at the following scenario:
Camera = Olympus OM-D EM5.
Things that matter (for me):
-Image quality in general (I read on DPreview that the 7-14 Pana's cromatic aberrations were discarded by in-camera software on Pana cameras, but not on Oly ones, is that an issue underwater?)
-Good for Close Focus Wide Angle.
thanks in advance for sharing your thoughts & experience :-)