Hi, I'm looking for a lens hood and series 7 filter retaining ring for a Leitz 90mm f2.8 R lens (first version, serial # 217xxxx). This lens has a built-in sliding hood, which I believe is held in place by the filter ring which screws onto the barrel's male thread (51mm). I'm actually not too bothered about the hood, the most importante thing would be to have a filter in place to protect the front element. Does the filter require the hood to secure it in place (as in the 28mm f2.8 R first version lens), or is it the other way around? I would be grateful for any information and advice on this. Eduardo Pacheco