Can anyone fill me in on the relationship between negative size and the height of the light source from that negative in the enlarger? Why is the head so much higher for a 35mm neg than for a 6x6 to 6x9? Why not closer for the smaller negative? Is this to even out exposure times from smaller to larger formats? This question stemmed from another post where I couldn't adjust the height of the condenser stage easily (it's broken) and someone recommended leaving it for a 6x9 and using 35mm and 6x6 at that setting as well--I would only see a very slight difference in printing quality.