Quote Originally Posted by munz6869 View Post
I have a blue filter accessory for my Grain focuser, and folks have often commented how sharp my prints are... Of course I have never ever used the thing (and why would I? It just makes everything annoyingly darker!).
Gene Nocon recommended the blue filter in his book Darkroom Printing. He suggested that it was better to focus using the same colour of light which the paper is sensitive too.

It doesn't matter if the light is filtered at the source or at the grain focusing device but I would remove it from the enlarger to make an actual print.