Originally Posted by Barry Oppenheim
Duane's 2006, Chapter 31, Physical Optics
"As a specific example, a ray impinging on the surface of an uncoated aspheric lens (refractive index, 1.523) near its edge at an angle of incidence of 58° would have a reflection loss of 8.3%. Lenses with steep front surfaces tend to produce larger angles of incidence and thus produce stronger reflections. However, by the addition of a single-layer MgF2 antireflection coating designed for normal incidence, the reflection loss is reduced by more than one half, to 3.6%. Only at angles of incidence larger than 60° does the reflectance of such a coated surface exceed 4%."
There you go. I'll also look in my copy of Hecht's Physical Optics (not at hand at the moment). It makes sense now that I think about it again.
The only question now is, why optosigma doesn't recommend coating aspherical lenses?