I just got a 300mm Componon S enlarging lens, a monster piece of glass. I will be using it on a cold light head enlarger for B&W printing. I plan on using two 4" square filters for contrast control. I once read somewhere about using two filters not specifically made for enlarging contrast control. I can't remember what filters were recommended. I'm thinking that it's likely that one is green, the other blue, but I'm not even sure of this. I tried a search here under "split filter printing" but was overwhelmed with the number of hits/responses. Does anyone out there know what I need? TIA, njb