Lovely photo's, but... to my knowledge there is no "Pentax-M 55mm K mount f1.8". Do you mean the "SMC Pentax 55mm f1.8", often refered to as the "Pentax-K 55mm f1.8", allthough lenses of this generation has neither a "M" nor a "K" in the name? This is a nice normal lense produced simultaneously to the original K generation bodies, the first Pentax K mount cameras, but the optical solution of this lens goes back to the Super/SMC Takumar 55mm lens and the spotmatics.
K 55/1.8
In the following "M" generation there were no 55mm lens, nor in the "A", "F", "FA" generations, but now there is a "DA*" 55mm!