This is a Nikon 16mm. f/3.5 Auto Fisheye (first version). There is a very small blemish about 1.5mm across and shaped like a doughnut. I've owned this lens for about 5 years and it was like this when I got it. I don't think it's fungus but not entirely sure, the rest of the front element and internals are flawless. Any idea what this blemish is? It looks much worse in the photo, the mark is more opaque.