Hi. The 40mm Focotar lens should give best results at f5.6. That is what Leitz recommend for normal use. With the colour head, using the dual filtration values from the Ilford data, sheet you should get exposures of 4 to 8 seconds for an 8x10 print. Check that you have not dialled in some cyan filtration and that the correct lamp is fitted. I don't think the lamp is adjustable on this model.