Howard beat me to it. Unless the dust isn't really dust (ie it's chunks) it won't show up in your images. It takes a truly amazing amount of interference to be visible. In addition to the link above (which directly addresses dust), have a look at this one that shows just how bad it has to get before you see stuff in the image. Executive summary: the lens has to be scratched in a pretty major way before ANYTHING is visible. This is FAR more than what you will find with virtually any kind of dust or dirt.
_____ Brian... a bicoastal Nikonian and Team Member
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