Extinction Correction and the [Fe ii] 1.26 μm/1.64 μm Intensity Ratio

From imaging observations of [Fe  ii ] emission in Herbig–Haro objects, I find a lower limit to the zero-extinction [Fe  ii ] 1.26  μ m/1.64  μ m intensity ratio of 2.6 and argue that this lower limit must be close to the true zero-extinction intensity ratio. My extinction determinations using this zero-extinction value yields results on well-studied HH objects consistent with results from other ionic-line spectra, whereas using nearly all theoretical values of [Fe  ii ] 1.26  μ m/1.64  μ m in the literature gives rise to unphysical results.