Protocol to dilute DNA step ladder?
You'll probably have to titrate it down yourself. You might be able to estimate: The detection limit for ethidium bromide staining is about $1 ng$ per band. The insert says it's at "1 $\mu g/ \mu l$", but that's for all 40 bands and they're clearly not all at the same concentration. Depending on which bands you care about (1600 and below are dim), you might be able to get away with $(\frac{1}{25})^{th}$ their recommended concentration (1 $\mu g / 40$ bands = 25 $ng$) -- but I would titrate a small amount and see what works.