Wonder why old 4/3rd lenses are slow on m4/3rd bodies?

Discussion in 'Digital Photography' started by RichA, Feb 27, 2012.

  1. RichA

    RichA Guest

    RichA, Feb 27, 2012
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  2. RichA

    Me Guest

    Perhaps there isn't any conspiracy, and perhaps it was already explained
    in an interview with a Panasonic executive a year or two ago.
    I haven't looked for the link, but IIRC his explanation was that they
    designed lenses for PD AF from the ground up with low mass moving
    elements for focus, with focus motors optimised for multiple fast
    incremental movements, as needed for fast CDAF.
    Which is /possibly/ why Canon and Nikon have seemed to be tardy with
    implementation of MILC in APS-c and FX formats. Perhaps Nikon are
    closer, as the "1" series hybrid AF system might work with their
    existing lens ranges in PD mode.
    Will be interesting when the big two do make a move, whether they use
    existing mounts (with extension tube) or new mounts.
    Me, Feb 27, 2012
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  3. RichA

    Bruce Guest

    The official explanation is that 4/3 lenses are designed for use with
    the phase detect AF systems of E-System DSLRs whereas m4/3 cameras and
    lenses use contrast detect AF.

    No, there isn't a conspiracy. You're being paranoid as usual.

    The article linked in that posting would have told you what I wrote
    Bruce, Feb 27, 2012
  4. RichA

    RichA Guest

    That really doesn't specifically answer why the lenses are so
    sluggish. Since you mention it, it appears they didn't implement
    circuitry in the new cameras that can distinguish between the phase
    and contrast focusing "features" of the lenses. This omission is due
    to one of two thing: They didn't have room or money for the circuitry
    in the new cameras, or they left it off on purpose, as they have focus
    confirmation with non m4/3rd lenses, a feature Nikon has had since (I
    believe) the D1X/D100.
    RichA, Feb 27, 2012
  5. RichA

    Bruce Guest

    I didn't say it did. I said that was the official explanation. In
    practice, the contrast detect AF system works exceptionally well with
    lenses that are designed for it.

    However, when you use a 4/3 lens that was designed for phase detect AF
    with a m4/3 body that has only contrast detect AF, the AF system
    hunts, often wildly, and can take as much several seconds to reach
    correct focus. Typically it takes about a second, which is really

    The problem seems to be that, when faced with an out of focus image
    from a lens that isn't optimised for contrast detect, the camera's AF
    system isn't able to decide which way to go to obtain correct focus.
    So it spends valuable time using trial and error instead - hence the

    Somehow, on the other hand, a lens designed for contrast detect will
    work together with the AF system to deliver near-instantaneous focus,
    because it not only knows which way to go but can tell approximately
    how far it needs to go. Even while it is moving towards correct
    focus, it is checking and re-checking the rate of increase of contrast
    and re-evaluating how far to go. All this seems to happen in the
    blink of an eye, because the AF systems on the latest Panasonic bodies
    are unbelievably fast and accurate.

    I don't pretend to know the detail of how the electronics in the lens
    and camera body work together. All I know is that it works, and at a
    speed I have never previously experienced. The G3, GH2 and GX1 all
    have this super fast AF, as does the Olympus E-P3 and possibly the
    E-PL3 and E-PM1, but I'm not sure about the last two.

    Now add a lens that doesn't have the necessary CPU, such as one from a
    4/3 DSLR, and you are back to good old-fashioned trial and error,
    which takes time. Typically a second, sometimes less, sometimes a lot
    more. And that's why people are frustrated and dissatisfied.

    But put a 4/3 lens on a 4/3 DSLR and it focuses quickly and accurately
    using phase detect AF.

    If you are going to put phase detect circuitry in to the cameras, you
    need phase detect sensors. Olympus and Panasonic won't be doing that,
    as it will add complication and cost that customers won't pay for.
    There is also the issue of royalty payments for in-sensor phase detect
    AF as used in the Nikon 1 System.

    I don't pretend to be an expert here. I am a very satisfied user of
    m4/3 and don't have any 4/3 lenses. I am told that we haven't had any
    complaints from customers - they seem happy to be able to use their
    4/3 lenses on their new m4/3 even if the AF is slow. So I think it is
    a problem that exists more online than in the real world, with people
    getting aerated about theoretical issues that don't have quite such an
    impact as they think on real life shooters.

    We have seen this phenomenon on newsgroups for years. People get
    extremely worked up about theoretical problems that are barely noticed
    in the real world. They obsess about things like the Nyquist
    frequency and MTF that may be of some relevance to designers of photo
    equipment but have far less relevance (often zero) to people who shoot
    images. Unfortunately, they cannot see the wood for the trees, and
    translating their claimed knowledge of the technology into capturing
    images that please, entertain and move people seems far beyond their
    Bruce, Feb 27, 2012
  6. RichA

    RichA Guest

    Remember when the Hubble telescope was first lauched? It has a very
    fine primary mirror, the most accurate figure and polish ever, but it
    was the wrong figure so it was spherically aberrated. Then they built
    the "Costar" which was an add-on corrective optics set that fixed the
    problem. What is surprising is that they literally can't work with
    the camera electronics to "adapt" the 4/3rd lens CPU outputs to work
    with the new contrast focus cameras. Nikon's V1 apparently works very
    well with phase lenses with the adapter they have.
    RichA, Feb 27, 2012
  7. RichA

    Bruce Guest

    That's because the Nikon V1 has phase detect AF. It would be very
    surprising if phase detect lenses did not work well on it.


    "Thanks to the lightweight elements inside their lenses, the J1 and V1
    focus very swiftly in good lighting using phase-detection AF. In poor
    light, autofocus switches to contrast-detection, but although still
    reasonably responsive, both cameras struggle much more to get an
    accurate focus 'lock'."
    Bruce, Feb 27, 2012
  8. RichA

    Bruce Guest

    I don't know if Panasonic or Olympus even entertained the idea. The
    on-sensor phase detect AF of the Nikon 1 system is (as far as I know)
    unique, and will be subject to very high royalties. So it can't have
    been an option for m4/3.

    True, but for the reasons I stated above, it was never going to
    happen. That's probably why Panasonic, Olympus and others have chosen
    to develop contrast detect AF to its full potential, and why the
    contrast detect AF in m4/3 is so much better than the contrast detect
    AF in Nikon's 1 System.
    Bruce, Feb 28, 2012
  9. So far, so fine.
    That would mean that the lens has an inbuild phase detection
    focus unit (or something to that effect). I know there were
    some AF lenses that AFfed on their own (without the camera),
    so that's not impossible --- just very unlikely in that case.

    What I'd assume is a very fast AF motor designed for near-instant
    accelleration and stopping of the (as light as possible) focus
    group. That would allow the camera to very quick get to the
    next test stop and reverse the direction near instantly if they
    overshot or went the wrong way. Add some heuristics with
    distance guessing, mix with an adapted binary search to
    update and confirm the heuristic guesses ...

    A phase detection optimized lens doesn't need instant stop
    and start, but would need high "long distance" moving speeds
    and stopping exactly on the right spot[1] (else a correction is
    needed, which takes time). Which also means the minimizing
    the focus group weight is not as pressing.
    Of course.
    Hmmm. Accurate --- well, if the focus stops are close enough
    to each other, then yes. (Imagine there are only 15 positions
    where the lens can/will stop. With a large sensor that's gonna
    not be enough.)

    Unbelievable fast --- for contrast AF. Not so for phase AF.
    Unfortunately. (At least that's what I hear.) But better contrast
    AF should "help" the phase AF makers to keep on improving and
    think of new ways to faster, more accurate AF.
    Of course, if contrast AF is 'fast enough', then customers won't
    pay. If the alleged speeds (I don't have first hand experience,
    so there) are as reported, that will be fast enough for many,
    maybe even most use cases (only excluding the real highest AF
    speed needs) --- which is fine! (I'll probably stay with
    DSLRs for a long time --- and the more camera companies make
    money, the more they have for developing better cameras,
    inclusive DSLRs.
    And maybe I want a better pocketable camera.
    And there are those who ignore well known problems because they
    are fanbois of some company, technology or feature, and see only
    the real or imagined or theoretical advantages. Like a --- purely
    hypothetical --- scene with --- imaginary --- light where only
    red pixels in bayer patterns would be triggered by the light,
    causing much less resolution, being a clear proof that Foveon
    is oh so much better. Or claiming that AA filters are, ah,
    not really needed on DSLRs.


    [1] which is distinct from instantly stopping. Though faster
    start and brake times can help, of course.
    Wolfgang Weisselberg, Mar 2, 2012
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