I am wanting to make a neg with 'ordinary' film and therefore need to convert from pan sensitivity. Although I suspect it may not be possible to make a true reproduction would it be a simple matter of using a blue filter? If that is the case is there any particular type or colour of blue filter or are all 'blues' the same? Would the Cokin type be suitable and what density? Density may only have effect on exposure time - but I don't know. Any suggestions?