Pentaxuser: When you use Y and M to control contrast it is the relative proportions of Y and M that determine contrast. If you dial in equal amounts of Y and M, from the paper's perspective you are dialing in "neutral density", because you are attenuating both blue and green light.
Originally Posted by pentaxuser
The logic would then be that the more neutral density you dial in, the less light the paper sees (although you can still see it because it is red). I think the point AgX is making is that even if you max out equal amounts of Y and M in a typical dichro head, there will still be too much blue/green light getting through for this to be "safe" for any extended period of time.