Use of an extender

Discussion in 'Photography Forums' started by chrishull3, Feb 20, 2014.

  1. chrishull3

    chrishull3
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    Any help will be appreciated ,It Says below
    1. Canon EF-S 55-250mm f/4-5.6 IS STM Lens Review
      The-Digital-Picture.com features Canon DSLR Camera and Lens Reviews, News, Deals and TipsReviews/Canon-EF-S-55-250mm-f-4-5.6-I...‎

      22 Oct 2013 - The Canon EF-S 55-250mm f/4-5.6 IS STM Lens is an inexpensive, light, entry level ..... This lens is not compatible with Canon Extenders.
    But is the lens compatible with any extenders,for instance a Kenko Teleplus Pro 300 AF DGX 2x review | Camera lenses Reviews | TechRadar
    This is a long shot i know but the price of very long lenses is beyond me at present.
     
  2. Dancook

    Dancook
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    TELEPLUS PRO 300 AF 1.4X DGX- KenkoTokina Global

    I believe the aperture will calculate as..

    2 x f4 = f8
    2 x f5.6 = f11.2

    So IF there is no compatibility issue with fitting it, you will not be able to use AF.
     
  3. chrishull3

    chrishull3
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    Yes i new about the maximum aperture being doubled with extenders,but i dont see how that affects AF,thanks for the reply.
     
  4. eddiewood

    eddiewood
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    Your cameras AF module requires a sufficient amount of light coming through the lens for it to work. If your lens maximum aperture is greater than f5.6, say f8 due to a teleconverter, then there may not be enough light hitting the AF module and you will lose AF.

    This is the reason why a f2.8 lens will AF, as even with a 2x teleconverter the maximum aperture is still within the f5.6 limit for the AF module to function.
     
  5. shotokan101

    shotokan101
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    As Eddie says - same as in poor light even at F5.6 some cameras/lenses will struggle/hunt for AF
     
  6. tapzilla2k

    tapzilla2k
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    Even with high end L lenses when an extender is used, the AF will not work properly. I think with a recent firmware update the 1DX will Auto Focus but at f/8 only (may have changed). Basically Canon disable AF when using the extenders for the above reasons mentioned , unless it's the 1D series. No idea about the 5D3 and if AF is disabled on that when using an extender. Some people tape the pins on lenses when using the 1.4 extender, probably something to attempt at your own risk. I doubt Canon would cover that under warranty.
     
  7. chrishull3

    chrishull3
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    Ok thanks,its a no go then,one thing of note my expensive Canon 1.5x Camcorder screw in lens works on the 55-250mm,it makes the lens a bit bulky though,the extra reach and less bulk of an extender like the Kenko would have been nice for wildlife.:(
     
  8. Bagger

    Bagger
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    I looked into this a while ago to see if I could use an extender with my ef-s 55-250 IS
    Its not just the auto focus at the smaller aperture. there's always manual if needed
    The ef-s lens (short back focus) physically sticks out further from the mount than an ef lens. So whether the lens will actually mount on the extender is the main problem. I've read you can use a short extension tube to get around this but you will lose infinity focus.
     
  9. shotokan101

    shotokan101
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    lens manufacturers sometimes manufacture a "dedicated" TC/"Extender" in such cases - know that a similar issue exists with some Sigma Lenses on Sony A-Mount......
     
  10. chrishull3

    chrishull3
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  11. Dancook

    Dancook
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    From Kenko's main PDF

    http://www.kenkoglobal.com/pdf/TELEPLUS_DGX_series_CompatibilityList.pdf
    So I assume this list is for both DG and DGX, I cannot be 100% sure.

    This list does not include the lens you have purchased, I can't find anything yet to suggest they are compatible - so good luck !
     
  12. shotokan101

    shotokan101
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    looks like the DG version is compatible so should work in MF mode...

    EDIT: - sorry - I misread it as the 70-300 EF-S - so as Dan says "good luck" - and let us know how you get on :)
     

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