last night I had to change the lamp on my M605. In the process I managed to knock the safety filter inline again, LOL. After two blank test strips the penny dropped. The point here is that I cannot easily see from the colour of the light whether the safety is in or not. One has to check on the enlarger itself. The more I think about it, the more it seems the safety filter could be your problem. A dirty lens could also give the symptoms. Do the prints look fuzzy or just flat? And what are your exposure times like? Minutes? Then it is definitely the filter. A fogged lens will not reduce exposure that much.