well, now that you mentioned ring adaptations... I only use canon for this kind of experiments... I prefer to leave my nikon line alone...
for example this selective focus pict:
is not made with a petzval, as one may expect, but with a medium format lens disposed into this outrageously simple rings setting:
I rarely use bellows in 35mm format, except for macro... I prefer large format for bellows, given the significantly greater circle covered by optics.
oh well, I guess I am totally out of our league with the last post... it has nothing to do with the subject anymore (most likely nothing to do with APUG!)