Have you ever heard of someone scratching their lens with a lens hood when putting it back on in reverse? The other night I was putting the lens hood on my 70-300 back on in reverse for storage, and accidentally slipped and I think it hit the glass. I am extremely OCD with my equipment and paranoid.... so now every time I use the lens I look at it from every angle in every bit of light that I can. Sometimes I think I see something... but then when I move slightly I can't find it again.
So, do you think its possible for a plastic lens hood to damage the lens or would it take much more than that to cause a scratch?

