I bet the question of how a dead fly inside a Canon EF 70-200mm f/2.8L IS II affects image quality wasn't something most of us would have ever seen tested, but alas, the folks at Lensrentals.com decided it was time to answer the query.
So, this seems like a good time to do a blog post showing that 1) this big-ass fly had almost no effect on image quality, so that little dust speck you’re frantic about sure doesn’t, and 2) getting flies (or dust) out of a lens is a lengthy and difficult process that takes a long time.
Now I think we all agree that the fly really did need to be removed, but by the time you finish this post, hopefully, you’re going to agree with me that that dust speck in your lens probably is just fine right where it is. Not to mention, I bet there’s a really good chance that if we remove this fly, the lens will never have another fly episode. If we remove some dust, though, there’s a 100% chance there will be more dust in the lens in a few weeks. Read the full article at Lensrentals.com
I'm quite glad we finally know the answer to this burning question!