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Thread: Is this sigma 17-70 ok?

  1. #1

    Default Is this sigma 17-70 ok?

    is below the correct way to check for FF and BF issue? is the below sigma 17-70 ok?
    if this is ok, does it means the focussing will also be ok for taking group photo using wide angle?

    17mm, 100% crop, focus on the dot


    70mm, 100% crop, focus on the dot
    Last edited by lizzy; 17th June 2007 at 03:01 PM.

  2. #2
    Member roentarre's Avatar
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    Default Re: Is this sigma 17-70 ok?

    Ideally, FF/BF should be checked on a testing chart with metering ...

    This lens is a good buy and I doubt FF/BF is less of an issue given its focal length range being quite "normal".

    Otherwise it is quite an performer (a bit large in size personally).

  3. #3

    Default Re: Is this sigma 17-70 ok?

    Quote Originally Posted by roentarre View Post
    Ideally, FF/BF should be checked on a testing chart with metering ...

    This lens is a good buy and I doubt FF/BF is less of an issue given its focal length range being quite "normal".

    Otherwise it is quite an performer (a bit large in size personally).
    thanks for the tip... i tested using the below and it looks fine
    http://focustestchart.com/chart.html

  4. #4

    Default Re: Is this sigma 17-70 ok?

    Quote Originally Posted by lizzy View Post
    is below the correct way to check for FF and BF issue? is the below sigma 17-70 ok?
    if this is ok, does it means the focussing will also be ok for taking group photo using wide angle?
    Although it might not be the best way to test FF or BF with a chart like what you used, I still think the lens seems more than okay

    Now go out and take some photos. If you are satisfied w/ what you get in the real world, then the lens is a good one

  5. #5

    Default Re: Is this sigma 17-70 ok?

    Quote Originally Posted by fengwei View Post
    Although it might not be the best way to test FF or BF with a chart like what you used, I still think the lens seems more than okay

    Now go out and take some photos. If you are satisfied w/ what you get in the real world, then the lens is a good one
    you are right! but testing is faster to determine if the lens is ok before the 1 to 1 exchange period is over..

  6. #6

    Default Re: Is this sigma 17-70 ok?

    I'd say it's off by about 0.5mm.. Time for exchange.. LOL

  7. #7
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    Default Re: Is this sigma 17-70 ok?

    The only way is to keep shooting photos, because when you start nitpicking on your photos you will know whether there is any FF/BF issues.

  8. #8

    Default Re: Is this sigma 17-70 ok?

    Hi
    This may not be related but I also did a test using a 50f1.4 with the following results some time back. Any comments on it?
    Cheers







  9. #9

    Default Re: Is this sigma 17-70 ok?

    looks ok to me, the focussing point is in focus...

    Quote Originally Posted by airconvent View Post
    Hi
    This may not be related but I also did a test using a 50f1.4 with the following results some time back. Any comments on it?
    Cheers







  10. #10

    Default Re: Is this sigma 17-70 ok?

    Thanks lizzy
    that's what I can see also but there is a variation between forward and backward focus.
    I am wondering if both sides of the focus should be symmetrical...

  11. #11
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    Default Re: Is this sigma 17-70 ok?

    Aiyah don't worry man, to be honest if there is any really big FF/BF issues you will only see it when you take proper actual photos.

  12. #12
    Senior Member creampuff's Avatar
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    Default Re: Is this sigma 17-70 ok?

    Quote Originally Posted by airconvent View Post
    Thanks lizzy
    that's what I can see also but there is a variation between forward and backward focus.
    I am wondering if both sides of the focus should be symmetrical...
    How can it be symmetrical? If you understand depth of field you will know that it always extends beyond more than forward of the point of focus.

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