I just picked up a 300mm f/4L from Craigslist last Thursday; I paid $900 and the lens looked to be in pristine condition and functioned perfectly with date code UW. I shot a soccer game and a few bird shots with it, and I found nothing wrong with the photos. Today when I was cleaning the lens, I put it up to my desk lamp and saw this inside:
Is this fungus? It is on one of the inner elements, and is just little dots arranged in a circle slightly smaller than the actual element. If it is fungus, how bad? Is it cleanable?
The seller said he bought the lens off eBay and only used it for a zoo trip. I don't believe he knew about the fungus when selling it though, it is impossible to see unless held to light. Then again, I'll never know. I don't know if I should try to return it, which is notoriously hard to do with Craigslist deals, or send it in to get checked out which would cost who knows how much, or just live with it?
Any insight is appreciated.