what is fungus on digital camera lenses and what is the remedy?

Answer 1

You had the camera and/or the lens stored away in a damp or humid place, maybe inside a dark cupboard in a dark room, causing fungus to grow inside the lens on the glass.

You could try putting the lens in sunlight for a few days to see if it kills the fungus and dries it up. If not, then you'll need to take it to a qualified camera technician and have them dismantle the lens, clean it, and rebuild it. This is, of course, an expensive thing to do.

Answer 2

You cannot remove fungus from any optical device...
better to take care not to allow its growth by keeping a beg of silica gel in the case with the camera, away from moisture... don't leave such devices in a car left in broad day sun shine... lest moisture would seep in and fungus would grow...