For B&W you can use the filter tray for variable contrast filters when using variable contrast papers. I'm guessing the the filter tray is above the lens. If you don't use a filter with variable contrast paper, they generally print at about grade 2 level, but exposure times will be quicker as the filters make the paper slower (this is a really bad explanation!) Alan will come along and make it a lot clearer!(posted 9053 days ago)