Seeing Clearly Through Clear Glass
He was concerned that the lens on his Nikon camera was playing up - that or the focusing screen. He said that when he took pictures of a bright light source on a dark field that he got "ghost" images all around the image. I was initally going to dismiss it as either a figment of his imagination or lens flare but I took his camera over to the bright LED lights on the new Nikon cabinet and looked.
You could see flare alright - no way you can expect not to. But there on either side of the main image were two separate faint images of the light. They moved around when you waved the lens past the light. Ghosts, but perfectly formed ones... ooeeooeeooeeooee...
A different lens showed none of this effect - you could get flare but no perfect little ghosts.
The culprit turned out to be an old uncoated Focal UV filter on the first lens. Clean enough, but every time you screwed it on the ghosts came back.
We screwed on a multi-coated UV filter from Kenko - not an expensive one, either. Ghosts exorcised!
Moral of this is listen to the customer, and throw out your old cheapjohn film filters and get some modern ones. There may be a lot of your image that is being obscured by ghosting right now that you do not even realise.