I remember you asked me about the built-in filters of the 15/3.5. I just relubed my lens last week and took a snap of the filter disc. The filters are actually SMC glasses, about 1mm thick and 1cm diameter (not exact). The edges of the filters are half perpendicular (up), and half 45 degree roughly (down). The filters actually fit the rims rather loosely, but were held by a few thin metal pieces as shown in the picture. To get to the filter disc, everything on both sides of the lens must be removed, except the focusing helicoid. There is nothing to calibrate so everything else should be pretty straight forward when assembling. BTW, the 2nd front lens group assembly should be turned clockwise to loosen, not anti-clockwise (but I don't know if this applies to all 15/3.5). Hope this help, if a little late. :-)
http://www.pbase.com/wlachan/image/38434710/original
You are a really brave and skilful man, Alan. I wouldn't dare to disassemble my A 15 mm. 3.5 in case it needed cleaning or lubing (happily it is in perfect shape). I am hopeless for such kind of delicate work.
Carlos
