Teleconverter: blurred at short focal length

Discussion in 'Nikon Lenses' started by Mamuang, Apr 28, 2017.

  1. Mamuang

    Mamuang TPF Noob!

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    Hi! I am using the 1,7x Nikon teleconverter with a 70-200mm/f2.8 and paradoxically the photos are blurred at a short focal length (e.g. 119mm) at a big aperture until I stop down up to f10 or so - but they are not when at 340mm under the same settings - so it is not a matter of depth of field or motion blur. How come??


     
  2. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Have you checked for back-focus?
     
  3. Mamuang

    Mamuang TPF Noob!

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    Well, there is no focus problem with the lens as such, and even with a long focal length at a wide aperture it is sharp. So it shouldn't be a back or front focus issue.
     
  4. PaulWog

    PaulWog No longer a newbie, moving up!

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    Minimum focus distance?

    Sample photos?
     
  5. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Which TC?

    Don't assume that focusing without the TC means there won't be focus issue with it. Check for back-focus to either confirm or eliminate it as the problem.
     
  6. table1349

    table1349 Been spending a lot of time on here!

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  7. Mamuang

    Mamuang TPF Noob!

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    I am using the Nikon AF-S Teleconverter TC-17E II with a Nikon 70-200mm/f2.8 VRII on a D810.
    There are no AF problems when shooting wide open at 340mm under the same conditions - so I exclude this as the culprit.
    The minimal focus distance is not undercut. It occurs with objects many meters away as well as with closer objects.
    I don't have a photo handy right now, but it's just an unsharp object anyway - no motion blur and no signs of front or back focus. These should be way more obvious at 340mm with f4.8 anyway...

    Could it be that the optimal aperture at 119mm with the teleconverter is just much smaller than with the other setting??
     
    Last edited: Apr 29, 2017
  8. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    But,........... how do you know this?
     
  9. Mamuang

    Mamuang TPF Noob!

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    Hm. Shouldn't that be much more apparent with the long focal length? I don't have a problem there at all - even at f4.8 ...
     
  10. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    The only way to know if it's back- or front-focusing is to test it.
     
    • Agree Agree x 1
  11. Mamuang

    Mamuang TPF Noob!

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    Well..... After a lot of puzzling out I now discovered that there actually is a front focus - but only at shorter focal length - with AF fine tuning "+3" it is better, but this is not the case with longer focal length. As I said, at 340mm and wide open it is sharp - without fine tuning only. How can this be? Do I have to activate fine tuning every time I want to shoot at the lower focal length range? ;(
    The lens itself, without the teleconverter doesn't have any front or back focus issues.
     
  12. Mamuang

    Mamuang TPF Noob!

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    I guess I'll send it back then...
    Thanks for your replies!
     

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