I got a brand new 85 1.8 a few months ago, which I inspected carefully when buying. I have used it only 3-4 times, and only twice outside, in my backyard for brief periods of time (15-20 minutes each).
This morning I changed lenses and noticed 2 small dust specks INSIDE the lens (behind the front glass). They are more like 2 very tiny pieces of fiber. I am sure that they do not affect the image quality, but I wonder how they managed to get into the lens.
I used the lens on my new 50D, so I am sure the dust was not from the camera. I use a lens hood all the time but I admit I did not use a UV/clear filter on the 85. I inspected my other lenses (24-105L, 50 1.4, 18-55IS, 135L). All of them are clean and have been used much, much more than the 85, both inside and outside. I only use filters in parks, zoo, playgrounds, etc. where the air can be dusty.
How did dust get into the lens? Could it have been avoided if I use a UV/clear filter?
I know this topic has been discussed to death, but it bothers me that my other lenses are used much more but OK.