Quote Originally Posted by Ian Grant View Post
It depends on the quality of coatings, and single coated is a misnomer as some coated (pre-MC) lenses have more than one coating layer. Another fly in the ointment is some manufactuers skimp by not coating every air/glass surface.

Let's start with the worst case. Hoya MC lenses, flare was so bad they scrapped the entire range and went back to the drawing board and launched a new range under their Tokina brand name. They'd not coated some internal air/glass interfaces.
Ian, your post makes the most sense to me. I have no expertise in the field of optics, but it seems to me that coatings become more and more important as the number of elements and glass-to-air surfaces increases.

My old 135/3.5 (four elements, three groups) has single coatings and my slightly more modern 18/4 (13 elements, nine groups) has more advanced multi-coatings, but the earlier, simpler telephoto definitely packs more of a visual punch.