Will phase focusing go the way of the dinosaur?

Discussion in 'Digital Photography' started by RichA, Jun 6, 2010.

  1. RichA

    RichA Guest

    Forget for the moment the benefits of going away from phase focusing,
    such as much lower cost going to contrast focusing. Phase's main
    important claim to fame is speed. But that is diminishing, or
    contrast is improving. The main problem with phase focusing is the
    constant problems with back or front focusing with various lenses,
    doesn't matter what brand of camera. This is a pain, one that
    contrast focusing apparently does not have or if it does, the
    incidence is very small. Most decent DSLR's now come with
    compensation features for this, but who wants to have to go though the
    elimination process for each lens they own and how often has this
    compensation not even been enough, or consistent?
     
    RichA, Jun 6, 2010
    #1
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  2. RichA

    Bruce Guest


    Only one brand has significant, systematic problems with AF accuracy
    and repeatability, and that is Canon. With all brands, there are of
    course the usual quality control issues, especially with tolerances
    that can cause problems. But only Canon has a system in which the
    problems are inherent in the design of the AF system.

    Canon has worked very hard to minimise these problems with firmware
    updates and more careful calibration of cameras and lenses. They
    haven't been eliminated, but they have been minimised to the extent
    that the vast majority of Canon users are not even aware of them.
     
    Bruce, Jun 6, 2010
    #2
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  3. RichA

    Twibil Guest

    "Will phase focusing go the way of the dinosaur?"

    You mean "will phase focusing eventually evolve into birds and remain
    very much on the scene for the forseeable future?"

    Seems unlikely.
     
    Twibil, Jun 6, 2010
    #3
  4. RichA

    Ray Fischer Guest

    And how many contrast-detection focusing systems can track moving
    objects at 10 frames per second?
     
    Ray Fischer, Jun 6, 2010
    #4
  5. RichA

    GMAN Guest

    There wasn't any T Rex's left after the great extinction to evolve into the
    chicken!!!
     
    GMAN, Jun 6, 2010
    #5
  6. RichA

    John A. Guest

    Not all dinosaurs were T Rexes.
     
    John A., Jun 7, 2010
    #6
  7. RichA

    John A. Guest

    If contrast focusing is immune to such problems, I could see including
    a contrast-based calibration system to ease determining the
    compensation for each lens. After that's set, it's phase all the way.

    I wonder if it would be possible to add to existing cameras with a
    firmware update, or if hardware designs limit the firmware's access to
    the autofocus system to merely activating & deactivating it and maybe
    switching between single and continuous modes. I would imagine the
    ones that do offer compensation settings could at least run through
    those and check them with contrast.
     
    John A., Jun 7, 2010
    #7
  8. RichA

    Wilba Guest

    More information please.
     
    Wilba, Jun 7, 2010
    #8
  9. RichA

    Rich Guest

    None, yet.
     
    Rich, Jun 7, 2010
    #9
  10. RichA

    Twibil Guest

    Um, yes, and that's because birds had already evolved from the dinos
    clear back during the Jurrasic; some 100 million years before Rex and
    his pals went belly-up.
     
    Twibil, Jun 7, 2010
    #10
  11. RichA

    Ray Fischer Guest

    And after all, focusing doesn't have to be as accurate with a 2MP camera.

    By the way, we've all seen how fast video cameras are at adusting to
    sudden changes in focus.

    Not very.
     
    Ray Fischer, Jun 7, 2010
    #11
  12. RichA

    Ray Fischer Guest

    Wishful thinking doesn't count.
     
    Ray Fischer, Jun 7, 2010
    #12
  13. You appear to forget that phase-focusing provides an instantaneous and
    continuous measurement not only of the direction of the focus error, but
    its magnitude as well, so that the camera knows which direction to move
    the lens, and by exactly how much to move it. One lens move. Focus done.

    Contrast focus, by comparison, takes time to evaluate how much in focus an
    image is, moves the lens in an arbitrary direction, evaluates the focus
    once again, has a 50% chance of finding the focus is worse so has to move
    the lens in the other direction, has to evaluate the focus again, move the
    lens, etc. etc., until the focus is worse again, so it's moved past the
    point of best focus, and finally has to move the lens back to /about/ the
    correct focus.

    "Will phase focusing go the way of the dinosaur?"

    No

    David
     
    David J Taylor, Jun 7, 2010
    #13
  14. RichA

    Bruce Guest


    You have a point, but these are down to operator error and, perhaps,
    some manufacturing tolerance problems which are there in all brands.

    The issue with Canon is different; the fundamental design of Canon's
    AF systems, especially those in the EOS 1D Mark III/IV, gives rise to
    systematic errors. These errors are such that they can only be
    partially compensated for in firmware and/or by recalibration of the
    camera body and/or lens.
     
    Bruce, Jun 7, 2010
    #14
  15. RichA

    Bruce Guest


    It also provides an estimate of the rate of change of sensor to
    subject distance, enabling predictive autofocus. That is not
    practicable with contrast detection AF, which means that cameras thus
    fitted are fundamentally less well suited to sports and wildlife
    photography, and also making images of children.

    I suspect that an active child is a more difficult subject to focus on
    than a bird or a racing car. ;-)
     
    Bruce, Jun 7, 2010
    #15
  16. RichA

    James Nagler Guest

    You appear to forget that some contrast focusing cameras are just as fast
    as phase focusing cameras today. Your desperate diatribe to justify
    phase-focusing sounds good in theory but doesn't hold up to reality. Catch
    up with this decade.
     
    James Nagler, Jun 7, 2010
    #16
  17. RichA

    SMS Guest

    Still a long way off in terms of speed. Compare a D-SLR in
    contrast-detect AF mode (live view on) with phase detect AF (live view
    off). If you need fast AF and/or a high frame rate then you can't get by
    with contrast-detect.

    The real question is if there will be any more P&S cameras that include
    contrast detect AF. I only know of one (a Ricoh model) that ever existed.

    The main problem with phase focusing is the
    Not really. Both Canon and Nikon have minimized this problem through
    firmware tweaks (at least with their own lenses, maybe it exists to a
    larger degree with third party lenses).

    Some people still complain about the Nikon AF system, whose slowness
    caused so many professional journalists to move to Canon (film D-SLRs)
    back in the 1990's and never go back (that and the fluorite lenses) but
    in D-SLRs Nikon has caught up, and in some cases surpassed Canon in AF
    performance.
     
    SMS, Jun 7, 2010
    #17
  18. RichA

    whisky-dave Guest

    So how did KFC evolve from KFT.Rex ?
     
    whisky-dave, Jun 7, 2010
    #18
  19. Full HD video is 1920x1080, which equates to 2.4MP, considerably less
    than the 12MP or whatever that the camera does in still mode.

    - Solomon
     
    Stuffed Crust, Jun 7, 2010
    #19
  20. []
    []

    A typo, I guess?
     
    David J Taylor, Jun 7, 2010
    #20
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