I just shined a flashlight on one of my "new" lenses tonight...and wow, it was dirty! A lot of dust and random particles on it... I tried using my Nikon lens pen to clean it, but there were still specks that look like it was dirty, but not scratches or marks in the lens. So, I was wondering, how do you guys keep your lenses clean without scratching it? I would love to get it absolutely perfect if I can. Thanks in advance!