Originally posted by mikeodial My understanding is on some other cameras the crop mode results in a very reduced (e.g. 5MP) image,
What camera is that? The D810 for example offers two crop modes: 1.5x which provides approximately a 16mp picture (k-5 size) and a 1.2x crop which provides approximately a 24mp picture (k-3 size). I'm not that familiar with Nikon so I don't know how easy it is to switch or when you would use one mode or the other.
But on Pentax, implementing such a feature would allow you to shoot at k-5 mp or k-3 mp or FF. (16mp, 24mp or 36mp). That assumes they use the 36mp sensor and implement 'crop mode' by allowing you to pick what you want rather than arbitrarily selecting a mode based on the lens mounted.
This is the way I would want to see it done because it allows your true APS-C lenses to work fine at 1.5x crop, the DA lenses that sort of work on full frame to be used at 1.2x crop and true FF lenses to be used fully.
I hope this is completely selectable as I have no problem with vignetting, I am happy to crop in post and get the most pixels possible with a given lens.
---------- Post added 04-10-15 at 11:30 AM ----------
And I am sure the TC is FF compatible, I believe that was in the initial press release from Ricoh.