According to the Durst catalog, the M805 B&W takes 150W opal lamp and the M805 Color a 250 W halogen lamp (Colamp 250 S). So 25 W is very underpowered, hence the long exposure times. The color spectrum of the bulb is important when using MC paper. The low contrast you are seeing suggests that the bulb temperature is too low, resulting in a preponderance of red light, to which the paper is not sensitive, and green light, which will only activate the low contrast emulsion on the MC paper. This would probably be the case with an ordinary incandescent bulb. Halogen bulbs are better since they operate at a higher temperature, giving more energy in the blue part of the spectrum which the high-contrast emulsion in MC paper is sensitive to. The problem with using a filter to correct this is that your exposure times, which are already long, will increase even more, especially if your bulb is an ordinary tungsten incandescent with little blue light to start with - a filter won't add blue light, it can only take away the excess green! My suggestion would be to see if you can't fit a 100W (or more powerful) halogen bulb.