Originally posted by awscreo Never tried the Q line, so it's a genuine question - what was unique about it?
A major extension of the depth of field, relative to all the other interchangeable lens systems, which have started from MFT upwards. Combined with the small size of the bodies. The historical precedent, on a different scale, was the Ur-Leica, but now that "miniature" format has become the norm against which we measure other systems (e.g., in using "full frame equivalent" focal lengths and apertures), and Leica has become more or less a boutique brand, that comparison may not be meaningful to a lot of people any more.
The other unique feature of the Q system, at least in present day terms, is the use of leaf shutters in all the high-end lenses, to give jello-free exposures. Because of their symmetrical action (as opposed to a focal plane shutter moving in one direction, or the flipping of an SLR mirror), you can get away with hand held shots down to very low shutter speeds.
All of this, and the sometimes unfortunate but often convenient fact that almost everybody regards them as a toy, means that they are the ideal "stealth" camera for use in concerts, temples, and other such locations.
Unfortunately, not all of the possibilities of the Q system were realized. One that bugs me is that Pentax never released the high-end telephoto macro lens (09), even though it reached the stage of working prototypes getting into the hands of some privileged users. This lens would have opened up a whole new photographic genre of action macro, which you obviously cannot do with focus stacking. As a kludge, you can use regular macro lenses on the K to Q adapter, but that setup will only work if you are able to anticipate and pre-focus on the action. The 09 would have offered autofocus, which works very effectively in the Q system. The Q's are the only cameras where I have never felt the need to second-guess the autofocus.
In terms of image quality, I would say that the Q matches 35 mm slide film from the 1970s, so good enough for the classic 10" x 8" or A4 size without any special technique or effort.
Since we're in an MF thread, let me summarize the Q system by saying that, relative to APS or FF, it expands your possibilities in the opposite direction to what you get with MF.