Damage caused by hot grinder sparks. This is a close up of damage to the coating of a cheap Sigma zoom (28-70mm) lens. The damage was caused by hot sparks from a hand-held grinder as it was grinding some steel. I had been going for some long exposure low light shots of the work being done. Unfortunately, I had gotten too close to the action. You can see in the image where hot bits of steel (or maybe it's carbon) have stuck to the lens. I haven't tried to use this lens since then, and in fact haven't even processed the film that I had shot that day (several years ago), so I don't know if this damage has degraded the (already poor) performance of the lens. Let this serve as a lesson though. If you have a lens that you value, don't try this at home! :-)