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Phillipsmetal
Tinkerer
Username: Phillipsmetal

Post Number: 1
Registered: 12-2012

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Posted on Monday, December 10, 2012 - 01:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

I recently carried my Nikon MF 300mm f 2.8 ED on a cross country motorcycle trip and when I returned the lens would no longer focus to infinity. At infinity on the dial, the lens would be focused at perhaps 100 feet, but would focus at distances less than that.

I am guessing that something in the screw mechanism that adjusts the focus has jumped a thread, but do not have the first clue what it would be. Does anyone have any idea what the problem would be and most importantly, if I can fix it myself? I have searched for parts break downs, etc. with no luck and hoped someone with experience with lenses would get me going.

Thanks, John
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Rick_oleson
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Username: Rick_oleson

Post Number: 1260
Registered: 07-2006

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Posted on Thursday, December 13, 2012 - 05:24 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Ouch! I certainly hope you're guessing wrong. I am not familiar with the 300/2.8, but most lenses have some means of adjustment between the focusing ring and the actual helicals, and hopefully this has just slipped out of position. In some Nikkors, this consists of 3 screws at the front end of the focusing ring, which clamp its front face against the front face of the focusing barrel. In others, the focusing ring is split under the rubber grip band, and just held together with a strip of adhesive tape. I'm sure there may be other variations, and I don't know which method the 300/2.8 would have used.

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