Yesterday, looking through the rear elements of my 480 symmar s after a cleaning oprations, I noted, on a very carefully inspection, some opacity between the lenses. It is something very similar to a glass wiped with a wet rag and then not polished with a dry one. In addition I must say this opacity not cover the whole surface of the lens, but only a little less than an half and is very difficult to detect, only in particular against light conditions. Can this opacity affect the performance of the lens? How can I eliminate this problem?
Since you say that the "opacity" is "very difficult to detect", probably you mean that the lens is less transparent than it should be, rather than being fully opaque in spots. From the description of "very difficult to detect", separation seems unlikely. More likely it is some substance coating a glass surface that you haven't cleaned, causing some haze. A haze like this can effect the performance of a lens because it scatters light into the shadows, reducing contrast. The first step is to try to clean the inner surfaces of the lens cells, as suggested in the first answer. This might fix the problem. But older lenses sometimes get a haze on internal surface -- this can be cleaned off, but the lens needs to be disassembled -- if this is necessary, you might want to have a repair person do the work.