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I did some searching for legacy lenses a while back and as far as I could find the Vivitar 105mm f2.5 macro was one of the best of its kind - and pricey. Adapters don't necessarily degrade the image on lenses they were designed for - some are a match and some are not. Kiron, Phoenix, Cosina and Panagor are other lenses you could look at. When these lenses were being made they were often the same glass and build available under different brands. I never considered the 100/f3.5, basically because I don't need more bits- adapter - but I'd say if you stick to the reputable ones you can't go wrong. Just be careful to ask all the right questions re glass/fungus, barrel and filter thread damage, aperture blade action/oil on them. Best to see it first.
One or two good ones here _ http://www.ebay.com/sch/i.html?_odkw=vivitar+series+1+macro&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313&_nkw=Vivitar+Series+1+105mm+f%2F2.5+Macro&_sacat=0
You could also look at the Oly OM 90/f2 ...