One of my favorite SLR lenses is Canon’s newer 50mm 1.8 STM. Optically it’s great, it’s super versatile, and at $120 it’s hard to justify not having if you’ve got any interest in primes at all. At that price, and with a front element actually buried kinda deep in the lens, it’s sort of silly to bother with a UV filter on the front. But then, I have bad luck with glass objects and scratching, so might as well.
Unfortunately, it seems like UV filters come in two sorts of construction. In one assembly, the glass element is sandwiched firmly into the metal thread housing, with another piece of metal holding it snugly in place. In another, the glass element is in the same thread housing, but with a snap ring simply retaining it, rather than holding it with a tight fit.
Well, my first Hoya HMC UV(c) filter was of the second type, and the glass floating around annoyed me. So I carefully dabbed a drop of superglue into the snap-ring groove on the inside of the housing in 3 spots – not actually on the glass itself, but where the ring met, simply to stop it floating around. Bad move.
Well, that filter’s toast.
Fast forward a few weeks and I’ve been using the lens without the filter, because, you know, it didn’t really need it in the first place. But on a sunny day in San Francisco, I noticed the lens was misbehaving in bright direct light. Flaring seemed worse than normal, even though you’d expect some shooting into the sun. What was much worse, the entire image seemed washed out in some frames, which I don’t remember ever seeing in the lens. So I took a look, and it certainly seemed like it had gunk on it. I wiped it down with a cloth, which didn’t help. I breathed on it for some moisture, then wiped that, and was horrified to see flecks of lens coating coming off on my microfiber. Oh god, what’s happening?!
In retrospect, I think the curing glue on the filter off-gassed solvent which attacked the coating on the lens just like it had on the filter. I didn’t notice at first, because the effect was generally uniform, but it resulted in the really bad washing out and the water-soluble coating that wiped away during cleaning.
Of course, I didn’t put that together at the time, since I’d long since stopped using the filter. Canon replaced the lens under warranty, whoops 😬
In the end, I actually kind of wish I’d kept the lens and just bought another. Obviously, it was totally messed up and pretty unpredictable to use in sun, but it was kind of fun for $120. As for the filter, funny thing: when I went back to Amazon to buy another for the new lens, the one that shipped suddenly said “Made in Japan” on it where the first one didn’t, and also didn’t use a snap ring – the new one had a much firmer fit that didn’t wobble. Go figure.
TL;DR: Don’t use superglue anywhere around optically coated anything, even if you think it’s probably dry by now.