It's not possible to assign raw/fx button to composition adjustment setting on K-3 (and after looking into K-3 II manual, it does not have it either). That makes me wonder. If it is true that the composition adjustment can be changed only on entering LV and cannot be changed during the LV session then I must say I don't quite understand that use case. Pentax most certainly did not forget about it or did not hide it as it is mentioned with other camera specific features on official website (
Specifications?K-3 | RICOH IMAGING). So I wonder whether I'm missing some smarter way of changing the adjustment or is it already smart and I just don't 'feel' it or did they remove it from raw/fx setting to make a room for something else or did they forget to put it there while redesigning FW for K-3 and then nobody noticed because nobody uses it?
I tried to play with it in order to add some field of view to wide angle lenses by simple stitch. I found not worth it unless I made sure camera is very firmly mounted on tripod during the whole procedure of changing the composition adjustment. Otherwise it becomes not much simpler than a regular stitching (i.e. requiring rotation, perspective etc. corrections). As far as I remember FLU card specs, it is not possible to make an adjustment from there either. Nor is it possible to anyhow 'program' it in advance. So I'm sure Pentax did not have stitching in mind when designing this feature.
I feel the perspective correction already shown in this thread is most likely the key use case. But still, why not allow for changing the adjustment during the whole LV session?