The flange to focal plane distance is probably too short. If so, adding spacers will just make it worse.
Add a filter into the adapter to see if that will extend the focal plane far enough. Each piece of glass that is N mm thick will extend the focal plane of the lens by about N/3 mm. Good filters are typically 3 mm thick, and that will extend the focal plane by 1 mm. That might be sufficient to make it work.
Chen
