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Thread: Lens Calibration

  1. #1

    Default Lens Calibration

    Well after shooting almost a year with my tamron 17-50 on my pentax camera, i do sometimes feel that my camera/lens is not focusing on the right target. So being a lazy person, i decided to do some calibration on this lens after a year. Did read up some guide in CS forum / youtube on how to calibrate. Although i do not have the optimum equipment (spyder calibration tools), i try to use a ruler on a white back grounded. Camera mounted on tripod adjusted to my so call 45 degree angle.
    focus is on the 2inch on the ruler.

    As per guide, people recommend to do a micro adjustment based on tele of the zoom lens (my case is 50mm) as DOF is more critical when focal length is at its tele range instead of wide. But i do find that on wide, it back focus too much when my tele is on focus. What do you guys think. Will making a trip to Tamron service Centre solved this problem or will they just blame it on camera issue and ,y way of testing?

    50mm at default (front focus)


    50mm at -10 micro adjustment ( spot on.. to my standard very happy almost going to celebrate)


    switch to wide angle and test
    17mm at -10 micro adjustment (alamak back focus.. WTH)


    17mm at default (change to default.. oei not bad although still got a bit of back focus)
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  2. #2

    Default Re: Lens Calibration

    Hi, To better understand how a lens focus mechanism work,have a read of how cnc (computer numerical control) machine system works.
    In principle it is similar.

    Precision ACME Leadscrew Nut

    The screw or leadscrew as it is known have backlash or error and anti-backlash nut is used to compensate.Similarly the lens group that is moving is
    part of this anti backlash assembly probably made of plastic and spring.Remember the lens assembly is moving forwards and backwards so there
    are 2 directions of error.I notice there is only a negative compensation value,is there no positive value? Or the design is such that error is in
    one direction only? As the default seems the best setting,what does that mean? Mechanical wear and tear? Which means no amount of compensation
    can correct? Which leads to the conclusion that replacement is neccessary? Is is worth the cost? Or something needs tightening? Worst case senario- live with it? That's why I like vintage manual lenses.I can "compensate" by eye and viewfinder but auto focus does have it's advantages and convenience.

  3. #3
    Moderator daredevil123's Avatar
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    Default Re: Lens Calibration

    TS, you really need to print a focus test chart to perform the test. You also need to mount your camera on a tripod, and you need good light. These things are required so your results can be consistent and accurate.

    You can download a free focus test chart here:
    focustestchart.com/focus21.pdf

    Follow the instructions attached.
    Last edited by daredevil123; 26th February 2012 at 03:20 PM.

  4. #4
    Moderator Octarine's Avatar
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    Default Re: Lens Calibration

    Spyder calibration for lens focus? Are you sure you were reading properly and the right stuffs? AFAIK, Spyder equipment is for monitor calibration, color reproduction. For the focus error on wide angle setting, do calculate the resulting DOF when your lens is at the wide end.
    Do use the focus test chart, the AF system is easily distracted if other lines are present as it is the case here with the ruler.
    EOS

  5. #5

    Default Re: Lens Calibration

    Focusing calibration for zoom lens is usually done on the wide & tele end at the service centres. For your case it is 17 & 50 mm.

    Unfortunately current bodies do not offer a separate zoom position micro-adjustment value so if you are unsatisfied you will either need to send it in to tamron or find an average adjustment value which gives acceptable performance for both tele & wide.

    Also I don't recommended calibrating too close to MFD... the minimum you should calibrate at is 25X the focal length which would be 1.25 m. It is also a common misconception that calibration is more crucial closer to MFD. Middle ranges suffer the most because there is lesser depth positions & too much depth at times which can throw AF off.
    Last edited by surrephoto; 27th February 2012 at 12:28 AM.

  6. #6

    Default

    Quote Originally Posted by Octarine
    Spyder calibration for lens focus? Are you sure you were reading properly and the right stuffs? AFAIK, Spyder equipment is for monitor calibration, color reproduction. For the focus error on wide angle setting, do calculate the resulting DOF when your lens is at the wide end.
    Do use the focus test chart, the AF system is easily distracted if other lines are present as it is the case here with the ruler.
    http://www.digital-photography-schoo...pyder-lenscal#
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  7. #7

    Default Re: Lens Calibration

    Quote Originally Posted by JinG14 View Post
    I didn't know such thing exist... isn't the test charts widely available online for free?
    Fujifilm X-Pro2 Graphite, X-Pro1
    XF 14/2.8, 18/2, 23/2, 35/1.4, 56/1.2, 60/2.4, 55-200/3.5-4.8

  8. #8
    Moderator Octarine's Avatar
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    Default Re: Lens Calibration

    Quote Originally Posted by JinG14 View Post
    Ah, ok.. another close of this device ..
    EOS

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