Autofocus Problem: I have Nikon D300 - with 55 lens the autofocus works just fine. However, it fails to function at all when I use the 200 lens. With the 200 the camera takes the picture but it is totally blurry, and does not make the usual autofocus beeping noise that accompanies the improved focus. When I try to manually focus with the 200 it also fails to focus. I am a novice but would appreciate any advice with troubleshooting.

SOURCE: autofocus will not work,

Camera wont let you take a picture until focus is locked, why are you using M (manual focus) if you expect autofocus to do it for you? In M mode it is up to you to focus correctly or camera will not take the picture.

SOURCE: Nikon 18-200 autofocus lens won't

OK I just fixed it, thanks to Ken Rockwell.com who says:

"Once in a blue moon my Nikon 18-200mm won't focus on my D200. Manual focus works fine, but the lens won't autofocus no matter what I do. It's annoying!
Of course the camera needs to be pointed at something with contrast, lines or texture. Point it at the sky and nothing autofocuses. That's normal.
One time this was so bad I thought for sure I was going to have to send my lens in for service, since nothing would get it to go.
Then I discovered the problem: I had knocked the AF switch on my D200 to M. This switch is easy to knock and I had forgotten to check the obvious. There also is a switch on the lens which is not easy to knock, but I have left the lens set to M shooting at night, and I forgot to return it to A/M the next morning.
This fixes most of my problems.
Rarer is when the lens honestly won't focus. When this happens I turn the camera off and on. If this doesn't fix it, turn the camera off, press the lens release button and rotate the lens back and fourth a couple of times. This will clear any dust off the electrical contacts and focus returns."

Steven Pepen

• 133 Answers
• Posted on Jan 03, 2011

SOURCE: Nikon d3000 autofocus issue

you should change the focus lock to AF-S, instead of AF-C