Lens ? Stupid question -- But I really need HELP.

Discussion in 'Photography Equipment & Products' started by zendianah, Oct 31, 2007.

  1. zendianah

    zendianah TPF Noob!

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    Hi there,
    I purchased a Sigma - 24-70mm 2.8 lens.... I hear that the Sigmas have good batches and bad batches... blah blah blah. My images seem to NEVER be sharp. I tryed all the advice that I get here.

    (kids -- use F11 with a faster shutter speed)

    Heres the stupid question part.... How can I test the lens for sharpness?-- Besides stating the obvious... take a picture and see if its sharp..obvious... I'm really embarrased about this question.. BUT I dont know who else to ask?

    Mods - If this idiotic question needs to be moved to beginners feel free.. I had no idea where to post.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    You can check to see if it's front or back focusing. An easy way to check is to put the camera on a tripod and shoot a ruler at a 45 degree angle. Set the focus on a particular point and shoot wide open. Then open the image and examine it...you are looking to see if the point that you focused on, is actually the sharpest part of the image. You could also use a book, magazine or newspaper...and just focus on a particular line of text.

    There are other ways to test a lens, try a Google search for 'lens test'.
     
  3. EOS_JD

    EOS_JD TPF Noob!

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    My Sigma 24-70 f2.8EX was soft wide open. Sharpened up well as it was stopped down. this was why I bought the Tamron 28-75 f2.8 and it was much better however I now use the 24-105 and the Tamron rarely gets out the bag (my brother has it at the moment)!
     
  4. zendianah

    zendianah TPF Noob!

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    Thanks Mike!! I'll try it out ! :)
     
  5. JerryPH

    JerryPH No longer a newbie, moving up!

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    My favorite was the focus test. You can download for free a PDF file, print ONE page out, and follow the instructions from the others... this is an easy test to do and will tell you right away if your lens front or back focuses.

    http://focustestchart.com/chart.html

    Enjoy!
     
  6. zendianah

    zendianah TPF Noob!

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    Thank you !! That is very useful!!! I just printed it out!
     
  7. itoncool

    itoncool TPF Noob!

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    Well, it's not a stupid question and I'm grateful you started this thread, zendianah. And thanks to you all.

    PS : I'm in the middle of the preparation, just printed out the chart too ;)
     
  8. zendianah

    zendianah TPF Noob!

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    I used the tutorial.. and my 2 main lens are sharp so its user error. :)

    Now I need to test my very used 80-200 lens -- I bought that one used so now I would have to work with the softness.
     
  9. JerryPH

    JerryPH No longer a newbie, moving up!

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    All my lenses (excluding the 30mm F/1.4 that I just ordered yesterday) are focusing properly too. I have seen a verson of the Sigma 18-50 with the Canon mount that front focuses about 10-12mm using that same test page... he is planning on sending it in with the test sheet to be hopefully re-adjusted.

    I'm glad to see that all your lenses are focusing properly!
     
  10. JerryPH

    JerryPH No longer a newbie, moving up!

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    The Sigma 18-50 is very sharp at F/2.8, but it is a completely other lens.

    [​IMG]

    [​IMG]
     
  11. kundalini

    kundalini Been spending a lot of time on here!

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    Front focusing - Back focusing. What should the lens be? If it's the other, how do you do the ring around - i.e. work with what you've got. Or should it be returned?
     
  12. Garbz

    Garbz No longer a newbie, moving up!

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    Sorry to nudge the topic a bit but the thread is all over the place anyway. How could back / front focusing possible be the fault of the lens? I don't see how this could be anything other than a camera fault and only something to do with the focusing screen being a different distance away from the mirror as the film plane. Yet I have seen constant discussions regarding lenses which are backfocusing.
     

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