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The 10% to 90% range in r is 20.6-21.1=0.5 mag=factor of 1.6. The 10% to 90% range in z (OH dominated) is 19.4-18.6=0.8 mag=factor of 2.
y band sky brightness varies over a night, from High, Stubbs et al PASP paper on y band variability:
Merit Function Ingredients.
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