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Thread: Buying a sharp copy lens from camerashop

  1. #1

    Default Buying a sharp copy lens from camerashop

    Hi,

    I am going to buy a Tamron 17-50 f2.8 for Pentax K-x. This is my 1st time buying lens only. i am thinking to buy it at SLR Revo. I am quite worried about getting a bad copy. how do you guys test the lens at the store? do you bring charts? Could anyone one give me advice? Thnks!

  2. #2
    Senior Member madmartian's Avatar
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    Default Re: Buying a sharp copy lens from camerashop

    Quote Originally Posted by Learnphotography View Post
    Hi,

    I am going to buy a Tamron 17-50 f2.8 for Pentax K-x. This is my 1st time buying lens only. i am thinking to buy it at SLR Revo. I am quite worried about getting a bad copy. how do you guys test the lens at the store? do you bring charts? Could anyone one give me advice? Thnks!
    Bring your camera there & test the lens with it. Take a few shots & zoom in from the preview screen to check its sharpness. Also make sure moving parts move smoothly.
    You don't need the whole lab team to be there just to purchase 1 lens
    Take the shot!

  3. #3

    Default Re: Buying a sharp copy lens from camerashop

    So i just
    1) use a simple test chart like this ---> lllllllllllllllllll
    2)with arms resting on a stable platform, focus the target at 45 degree with lens wide open at F2.8 and from 17mm, 35mm, 50mm
    3)using LCD, check if the target is the sharpest line

    is it a need to test with lens at F8 F22? just wide open will do?

    if the target is in focus but is NOT at the center of the focus range, is it suffering front/back focusing?

  4. #4
    Moderator Octarine's Avatar
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    Default Re: Buying a sharp copy lens from camerashop

    Quote Originally Posted by Learnphotography View Post
    is it a need to test with lens at F8 F22? just wide open will do?
    The very basics about Depth of Field should tell you why the test is done at the widest aperture. How does the DOF change when you close aperture? How likely is it to find a focusing error then?
    if the target is in focus but is NOT at the center of the focus range, is it suffering front/back focusing?
    This is provided there is no other error or problem in your test setup. Chances of human error are usually higher than chances of technical faults. Keep in mind that the focus sensors in the camera are bigger than viewfinder markings. Be careful when focusing, especially hand held. Also, before you setup all your test charts and block half the shop you can simply verify the 7 days 1:1 exchange policy that many other shops have. Get the lens and test at home. Don't forget a tripod.
    EOS

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