I used my 1946-47 IIIc with my 1936 50mm f SUMMAR . It gave some flare even though I had painted the lens hood with Matt Black Paint I guessed the focus as photos were taken at waist level.
I've had the X1 for a couple of weeks now and I'm just starting to get used to it. It is a delight to use. Forget the negative stuff - it's just superb in everyday use.