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Message: <blockquote data-quote="hark" data-source="post: 835318" data-attributes="member: 13196"><p>Glad you were able to resolve your issue. I was having AF problems with my Nikon 300mm f/4 PF and sent it out to Nikon repair. They couldn't find anything wrong and returned the lens. Eventually I used 99% Isopropyl Alcohol which is for technical use  (higher concentration of alcohol than Rubbing Alcohol but doesn't sanitize) to clean contacts on my lens. When applying it with a Q-Tip, I started to get black sticky stuff of the contacts which reminded me of tar. The lens works fine now. The thing is the black stuff wasn't visible to the naked eye so I had no idea it was even there. Somehow Nikon missed it or didn't bother to clean the contacts.</p></blockquote><p></p>