A customer at my bench in Grand Rapids told me to quit cleaning lens edges with canned air, and I owe her one
She was picking up a 50mm and watched me blast dust off the rear element before I put it back together. She said the propellant in cheap canned air can spit and leave a film on the coating, and that she'd seen it happen on a $400 lens. I switched to a rocket blower and a dry lens tissue for the edge work, and I haven't had a single smeary element since. Has this happened to anyone else, or do some of you still keep a can around for the stubborn stuff?