Sigma 120-400 Hunting

cape codcape cod Registered Users Posts: 52 Big grins
edited November 25, 2011 in Cameras
Just recently noticed that when my Sigma 120-400 is focusing anything above 120 mm it is hunting for a focus area. Have done the usual .. checked that the AF was on the lens as well as my Nikon D300s ..changed focal areas ..it will definitely focus properly at 120mm but starts to act up soon as extend out .. don:dunno

Comments

  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited November 23, 2011
    Is this occurring mostly at lower light levels?
    What is the subject matter?
    Shine a pointilistic light source through the lens (off the camera), frontwards and backwards. Do you see any internal haze? (I use a small, single white LED flashlight for this purpose.)
    ziggy53
    Moderator of the Cameras and Accessories forums
  • cape codcape cod Registered Users Posts: 52 Big grins
    edited November 25, 2011
    ziggy53 wrote: »
    Is this occurring mostly at lower light levels?
    What is the subject matter?
    Shine a pointilistic light source through the lens (off the camera), frontwards and backwards. Do you see any internal haze? (I use a small, single white LED flashlight for this purpose.)

    Ziggy .. spent quite a bit of time this after .. light or dark conditions are the same .. subject doesn't make any difference .. keeping at 120 mm focus's as it should .. when I pull it out to a longer length it has all kinds of issue focusing , look carefully with a light source both directions. did not see any haze..thanks don
  • ThatCanonGuyThatCanonGuy Registered Users Posts: 1,778 Major grins
    edited November 25, 2011
    Maybe cleaning the contacts would help (if you haven't tried it already).
  • cape codcape cod Registered Users Posts: 52 Big grins
    edited November 25, 2011
    That's a good point .. What would you suggest for a cleaner ..
  • ThatCanonGuyThatCanonGuy Registered Users Posts: 1,778 Major grins
    edited November 25, 2011
    A pencil eraser should work thumb.gif
  • ziggy53ziggy53 Super Moderators Posts: 24,156 moderator
    edited November 25, 2011
    cape cod wrote: »
    Ziggy .. spent quite a bit of time this after .. light or dark conditions are the same .. subject doesn't make any difference .. keeping at 120 mm focus's as it should .. when I pull it out to a longer length it has all kinds of issue focusing , look carefully with a light source both directions. did not see any haze..thanks don

    Double check to see if you are in continuous focus mode. (Should use one-shot AF mode for stationary subjects.)

    Put the lens in manual focus mode and see if you can achieve focus confirmation.
    ziggy53
    Moderator of the Cameras and Accessories forums
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