Durst 670M COLOR clear spots from the light box or color filters

Hello All!, I use my Durst 670m Color as the light source for large format (8x10 and 11x14) contact printing, using the color head for contrast control of the variable contrast paper. Lately have seen small light spots in the dark areas of the prints, that keep the same position from print to print, and are particularly well seen printing in high contrast filtration mode. They do not come form the printing press, nor from the lens (maintain the position despite rotating the lens) nor from outside the enlarger, and they seem to come from above the lens - likely the light box or the variable contrast filter system). Any recommendation about how to clean the light box or the filter system on this enlarger?

Thanks in advance!, the spots are a nuisance!!

Eliseo Pascual
Spain

How are you focusing the lens (I suspect you are using a lens, yes?). Maybe your lens is focused on the diffuser plastic. Try focusing to an area where the negative would be, to put the diffuser out of focus.

Thank you, I had not think about that. To use the enlarger as a light source for contact printing, better to have everything our of focus!