Pentax ist ds infinity focus problem

Discussion in 'Digital Photography' started by grevillea, May 16, 2005.

  1. grevillea

    grevillea Guest

    Pentax ist ds---camera repaired for autofocus problem---reverted to
    closest focus most of the time.

    Now infinity seems to be out---infinity is slightly off the far right
    turn stop---tested using the landscape mode and autofocus and confirmed
    with manual focus. expected infinity to be as far to the right as I
    could go.

    Is this a problem? does it need to go back for more repairs (the last
    set took 4 weeks!!!)?

    anyone else have this problem?
     
    grevillea, May 16, 2005
    #1
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  2. grevillea

    Justin Thyme Guest

    It is normal for lenses to focus slightly beyond infinity (if that makes
    sense). If the lens was designed so that infinity fcous was at it's extreme
    position of operation, you would find situations where you wouldn't be able
    to achieve infinity focus. For example temperature changes or even a bit of
    crud on the lens mount would be sufficient to stop the lens focussing to
    infinity. Therefore they design the lens to focus a little beyond infinity
    so that there is enough provision left in it to allow for temp changes etc.
    it ain't a problem - every single SLR lens is designed like this, if it
    wasn't then you would have problems.
     
    Justin Thyme, May 16, 2005
    #2
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  3. grevillea

    grevillea Guest

    Thanks for the info---this is my first SLR digital---guess I have alot
    to learn.
     
    grevillea, May 16, 2005
    #3
  4. grevillea

    Colin D Guest

    Autofocus needs the 'beyond infinity' space to operate properly.

    Colin
     
    Colin D, May 17, 2005
    #4
  5. grevillea

    JohnR66 Guest

    I've always heard this and it does make sense, but all my older Pentax and
    Nikkors would stop right at infinity. These lenses seemed to be much finer
    quality (and very sharp) optical instruments with tight tolerances. Now
    everything has lots of plastics in the design and some of the lenses feel
    somewhat loose. I'd say the extra focus adjustment past infinity is
    allowance for slop in the design and possible the extra coefficient of
    thermal expansion of plastics as compared to metals.

    John
     
    JohnR66, May 17, 2005
    #5
  6. grevillea

    Paul Furman Guest


    I heard people talk about carefully manually focusing on the moon. WTF?
    I don't get that? Shouldn't infinity be good enough???? I think they
    were dead serious though. I have no clue.
     
    Paul Furman, May 17, 2005
    #6
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