I have always used it undiluted. It seems to last all day in a tray doing 8x10's or 11x14's. I guess I will see what I get with it diluted 1:1. Some of my recent uploaded images in the gallery are done with PPPD straight. Great developer. I like the deep blacks I got with the Efke PL-25 and this developer. I always thought it was to be used straight. Maybe Donald will chime in on this. I guess whatever works best for your vision is what you should use.