DAG made me a filter adapter for the Summitar by taking an old Summitar filter with bad glass (which I supplied), removing the glass and gluing in a 39mm female thread. This worked nicely on the M8, where I needed to use an IR cut filter). He warned me that it might vignette on full-frame Leicas. I haven't tried yet. IIRC he recommended making a Summitar to 46mm adapter for film or full frame. This is probably something that any competetent and willing repair person could do.