Panasonic's contrast focusing puts them miles ahead of anycompetition

Discussion in 'Digital Photography' started by RichA, Sep 24, 2009.

  1. RichA

    RichA Guest

    Sony and Samsung are now talking about going with a mirror-less
    interchangeable lens camera. But the focusing system in the
    Panasonic's is better than anything in DSLRs at the moment. If there
    is a large shift to mirror-less systems, companies like Nikon which
    boast outstanding phase focusing systems will likely work harder on
    their rather pedestrian contrast focusing systems used in current
    products with live view.
     
    RichA, Sep 24, 2009
    #1
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  2. RichA

    Miles Bader Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    RichA <> writes:
    > But the focusing system in the Panasonic's is better than anything in
    > DSLRs at the moment.


    Is it? How does that work anyway?

    My understanding is that using the information read from the focusing
    sensor in a phase-based system, you can deduce the direction and amount
    of adjustment needed (to some degree anyway), and also whether or not
    you're at the point of best focus; this information helps a lot to
    reduce hunting.

    The information available from the sensor in a contrast-based system, on
    the other hand, is much harder to interpret -- you can't even really
    tell if you're at the point of best focus or not without adjusting the
    lens and seeing whether the contrast is reduced or not.

    That makes it sound _very_ difficult for a contrast-based system to be
    as good as a phase-based system, since there's going to inherently be
    some hunting with the contrast-based system. The only way I can think
    of is to make the focusing motor so fast and powerful that the hunting
    becomes unnoticeably fast...

    -miles

    --
    P.S. All information contained in the above letter is false,
    for reasons of military security.
     
    Miles Bader, Sep 24, 2009
    #2
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  3. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, Miles Bader
    <> wrote:

    > RichA <> writes:
    > > But the focusing system in the Panasonic's is better than anything in
    > > DSLRs at the moment.

    >
    > Is it? How does that work anyway?


    it's better than other contrast detect systems and comparable to entry
    level dslrs, but it is certainly *not* 'better than anything in dslrs
    at the moment' nor is it anywhere close to top end dslrs such as the
    nikon d3.

    > That makes it sound _very_ difficult for a contrast-based system to be
    > as good as a phase-based system, since there's going to inherently be
    > some hunting with the contrast-based system. The only way I can think
    > of is to make the focusing motor so fast and powerful that the hunting
    > becomes unnoticeably fast...


    part of it is the lens motor. the panasonic g1 does not focus as fast
    with older 4/3rds lenses.
     
    nospam, Sep 24, 2009
    #3
  4. RichA

    Miles Bader Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    John Navas <> writes:
    >>My understanding is that using the information read from the focusing
    >>sensor in a phase-based system, you can deduce the direction and amount
    >>of adjustment needed (to some degree anyway) ...

    >
    > That's the theory, but it's not that simple in practice. The direction
    > and amount of focusing depends on the lens and focusing mechanism, and
    > to prevent focus error, a good phase detection system will touch up
    > (hunt) focus.
    >
    >>The information available from the sensor in a contrast-based system, on
    >>the other hand, is much harder to interpret -- you can't even really
    >>tell if you're at the point of best focus or not without adjusting the
    >>lens and seeing whether the contrast is reduced or not.

    >
    > Again, it's not that simple in practice. A good contrast detection
    > system can use such things as predictive focus, focus tracking, and
    > continuous focusing, making focusing very fast in many cases.

    ....

    Yeah, of course things are always more complicated in practice, but the
    point is that there's inherently more information available with
    phase-based auto-focus systems. Even very rough information that lets
    you guess how far out of focus you are, and in which direction, is very
    useful (especially the "which direction" bit!), and contrast-based
    sensors don't provide anything like it.

    Of course you can use the techniques you mention to try and speed up the
    "hunting" process, but they're at best educated guesses, and a poor
    substitute for getting more useful information from the sensor.

    Moreover, you can of course use the same techniques to make a
    phase-based focusing system even better, so the original claim that a
    contrast-based system on a relatively low-priced camera is better than
    phase-based systems on expensive cameras seems ... rather dubious.

    -Miles

    --
    Genealogy, n. An account of one's descent from an ancestor who did not
    particularly care to trace his own.
     
    Miles Bader, Sep 24, 2009
    #4
  5. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, John Navas
    <> wrote:

    > The reality is that both systems have pros and cons, that good
    > implementations of both systems involve some hunting, that both systems
    > can be made to work very well, and that claiming one is "better" than
    > the other is silly and pointless trolling.


    nonsense. it's not trolling. phase detection is faster.

    currently, the fastest contrast detect autofocus is about as good as
    the slowest phase detect autofocus.

    until contrast detection is as fast or faster than the fastest phase
    detection, phase detection is very clearly better.

    whether someone wants fast autofocus is another story. some people
    prefer manual focus, which can be 'better' in certain scenarios, such
    as macro.
     
    nospam, Sep 24, 2009
    #5
  6. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, John Navas
    <> wrote:

    > >> The reality is that both systems have pros and cons, that good
    > >> implementations of both systems involve some hunting, that both systems
    > >> can be made to work very well, and that claiming one is "better" than
    > >> the other is silly and pointless trolling.

    > >
    > >nonsense. it's not trolling. phase detection is faster.
    > >
    > >currently, the fastest contrast detect autofocus is about as good as
    > >the slowest phase detect autofocus.

    >
    > Simply not true.


    it's exactly true.
     
    nospam, Sep 24, 2009
    #6
  7. RichA

    Miles Bader Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    John Navas <> writes:
    >>Yeah, of course things are always more complicated in practice, but the
    >>point is that there's inherently more information available with
    >>phase-based auto-focus systems. Even very rough information that lets
    >>you guess how far out of focus you are, and in which direction, is very
    >>useful (especially the "which direction" bit!), and contrast-based
    >>sensors don't provide anything like it.
    >>
    >>Of course you can use the techniques you mention to try and speed up the
    >>"hunting" process, but they're at best educated guesses, and a poor
    >>substitute for getting more useful information from the sensor.

    >
    > They work actually very well in practice.


    I'm predictive methods help, but let's just say, that I'm skeptical that
    they help enough to make contrast-based focusing as good as phase-based
    focusing.

    Remember that the original poster's claim was: "the focusing system in
    the Panasonic's is better than anything in DSLRs at the moment."

    _That_ seems very surprising, and hard to understand. Since the
    original poster didn't offer much in the way of evidence or explanation,
    I'm trying to figure out if what he said is actually true, and if so,
    how they pulled it off given the inherent speed deficiencies of the
    contrast-based method.

    Do you see _why_ a phase-based system offers more information? The
    sensors in a phase-based system give you information about "out of
    focusness". That makes it easier to know (1) when you should stop
    focusing, (2) the likely direction the focus should change (3) how fast
    you should try to change the focus to correct the focus.

    The sensor in a contrast-based system doesn't tell you any of that. It
    merely gives you a contrast measurement, which is only meaningful for
    focusing purposes if you compare it with a contrast measurement at
    another focus setting -- so the contrast-based system cannot actually
    tell you anything without at least some movement of the focus, and
    perhaps more crucially doesn't give you information about when you
    should stop or how fast you should go. By taking measurements at
    multiple points of focus you can build up the required info, but it
    inherently requires the focus motor to keep moving beyond the point of
    correct focus (because it can only tell if it's gone too far by noticing
    that the contrast starts to drop again). It also doesn't know how fast
    it should move, and if it drives the focusing motor very fast, it can
    easily overshoot and may not realize it!

    Anyway, it certainly seems _possible_, with a very fast focusing motor
    and high sampling rate, to make this work reasonably well, but it's very
    surprising if it works better than the phase-based system used in DSLRs.

    -Miles

    --
    "Suppose He doesn't give a shit? Suppose there is a God but He
    just doesn't give a shit?" [George Carlin]
     
    Miles Bader, Sep 25, 2009
    #7
  8. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, Miles Bader <>
    wrote:

    > Remember that the original poster's claim was: "the focusing system in
    > the Panasonic's is better than anything in DSLRs at the moment."
    >
    > _That_ seems very surprising, and hard to understand. Since the
    > original poster didn't offer much in the way of evidence or explanation,
    > I'm trying to figure out if what he said is actually true, and if so,
    > how they pulled it off given the inherent speed deficiencies of the
    > contrast-based method.


    that claim is not true. the panasonic g1 is among the fastest contrast
    detection systems and comparable to low end dslrs, but it is not faster
    than every dslr available.

    <http://www.dpreview.com/reviews/panasonicdmcg1/>

    And our initial tests would suggest that they have solved at least
    one of the technological problems mentioned earlier (the
    contrast-detect autofocus is easily as fast as any other entry-level
    DSLR).
     
    nospam, Sep 25, 2009
    #8
  9. Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In rec.photo.digital John Navas <> wrote:
    > On Thu, 24 Sep 2009 17:22:14 +0900, Miles Bader <> wrote in
    > <>:


    >>RichA <> writes:
    >>> But the focusing system in the Panasonic's is better than anything in
    >>> DSLRs at the moment.

    >>
    >>Is it? How does that work anyway?
    >>
    >>My understanding is that using the information read from the focusing
    >>sensor in a phase-based system, you can deduce the direction and amount
    >>of adjustment needed (to some degree anyway), and also whether or not
    >>you're at the point of best focus; this information helps a lot to
    >>reduce hunting.


    > That's the theory, but it's not that simple in practice. The direction
    > and amount of focusing depends on the lens and focusing mechanism, and
    > to prevent focus error, a good phase detection system will touch up
    > (hunt) focus.


    The problem with doing that is that it might involve a change of
    direction, which would involve taking up the backlash in the focus
    motor drive. A switch of direction which involves drive backlash is
    too much for an efficient tightly wound servo control loop to handle,
    so it's done as separate a invocation of the "start focussing again
    from scratch" general focus routine. Which all takes a little time.

    That's why even better phase focus systems will drop the focus motor
    speed down in the final approach to the focus destination so that the
    destination can be approached with maximum precision by monitoring the
    phase readings during the final approach. That way the best focus is
    achieved without having to restart (and possibly reverse) the
    focusing. Also copes with minor relative movements of camera or
    focussed object during the focus procedure.

    --
    Chris Malcolm
     
    Chris Malcolm, Sep 25, 2009
    #9
  10. RichA

    Rich Guest

    On Sep 24, 12:35 pm, nospam <> wrote:
    > In article <>, Miles Bader
    >
    > <> wrote:
    > > RichA <> writes:
    > > > But the focusing system in the Panasonic's is better than anything in
    > > > DSLRs at the moment.

    >
    > > Is it?  How does that work anyway?

    >
    > it's better than other contrast detect systems and comparable to entry
    > level dslrs, but it is certainly *not* 'better than anything in dslrs
    > at the moment' nor is it anywhere close to top end dslrs such as the
    > nikon d3.


    Yes, my apologies, I worded that wrong, I mean live view contrast
    systems in DSLRs.
     
    Rich, Sep 25, 2009
    #10
  11. RichA

    Wilba Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    Miles Bader wrote:
    >
    > Anyway, it certainly seems _possible_, with a very fast focusing motor
    > and high sampling rate, to make this work reasonably well, but it's very
    > surprising if it works better than the phase-based system used in DSLRs.


    True for certain definitions of "better", but not all. You seem to be
    speaking only of speed and efficiency.

    In my experience with getting the phase detect AF of a 450D sorted, the PD
    system is never more accurate than the contrast detect system (with
    reasonably well lit subjects). The accuracy of the PD system is directly
    dependent on careful calibration of all components, whereas the accuracy of
    the CD system is not.
     
    Wilba, Sep 26, 2009
    #11
  12. RichA

    Miles Bader Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    "Wilba" <> writes:
    > The accuracy of the PD system is directly dependent on careful
    > calibration of all components, whereas the accuracy of the CD system
    > is not.


    Hmm, it's certainly dependent on the alternate optical path (to the PD
    sensors) having the same length as the actual image path, but that's
    true of all traditional focusing systems (SLR focusing screens,
    rangefinder optics, etc), so it's obviously an issue that's been well
    handled for a very long time.

    For that reason, though, a CD system may be a better choice for very
    cheap cameras, as it's less affected by poor tolerances in construction.

    -Miles

    --
    Rational, adj. Devoid of all delusions save those of observation, experience
    and reflection.
     
    Miles Bader, Sep 26, 2009
    #12
  13. RichA

    Wilba Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    Miles Bader wrote:
    > Wilba writes:
    >>
    >> The accuracy of the PD system is directly dependent on careful
    >> calibration of all components, whereas the accuracy of the CD
    >> system is not.

    >
    > Hmm, it's certainly dependent on the alternate optical path (to the PD
    > sensors) having the same length as the actual image path, but that's
    > true of all traditional focusing systems (SLR focusing screens,
    > rangefinder optics, etc), so it's obviously an issue that's been well
    > handled for a very long time.


    Not always well handled. A significant number of 450Ds (including mine) need
    to be returned to Canon for calibration before their PD AF works within
    Canon's specification. I don't know if the defect rate is very different for
    that model compared to others, or it's just that the 450D has become
    renowned for it.

    > For that reason, though, a CD system may be a better choice for very
    > cheap cameras, as it's less affected by poor tolerances in construction.


    And for the same reason CD AF is the choice for ultimate accuracy when speed
    isn't a requirement.
     
    Wilba, Sep 26, 2009
    #13
  14. Miles Bader <> wrote:

    > Hmm, it's certainly dependent on the alternate optical path (to the PD
    > sensors) having the same length as the actual image path,


    Actually, not for AF. A PDAF depends on knowing the correct
    offset. If the alternate optical path is 1mm longer and the
    lens gives the best *overall* results for all wavelengths when
    defocussed a tiny amount from the wavelenghts the AF is most
    sensitive for --- no problem, just add up the 2 offsets, don't
    drive the focus motor to where the AF sees most clearly but to
    the combined offset from that position and all is well.

    > but that's
    > true of all traditional focusing systems (SLR focusing screens,
    > rangefinder optics, etc), so it's obviously an issue that's been well
    > handled for a very long time.


    That's true.

    > For that reason, though, a CD system may be a better choice for very
    > cheap cameras, as it's less affected by poor tolerances in construction.


    It's certainly cheaper. Large format uses a form of CD focussing,
    it's called ground glass and is then replaced by the sensor
    plate/film box/whatever. :) That works well, but is not really
    suited to action photography.

    -Wolfgang
     
    Wolfgang Weisselberg, Sep 27, 2009
    #14
  15. Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In rec.photo.digital Wilba <> wrote:
    > Miles Bader wrote:
    >> Wilba writes:
    >>>
    >>> The accuracy of the PD system is directly dependent on careful
    >>> calibration of all components, whereas the accuracy of the CD
    >>> system is not.

    >>
    >> Hmm, it's certainly dependent on the alternate optical path (to the PD
    >> sensors) having the same length as the actual image path, but that's
    >> true of all traditional focusing systems (SLR focusing screens,
    >> rangefinder optics, etc), so it's obviously an issue that's been well
    >> handled for a very long time.


    > Not always well handled. A significant number of 450Ds (including mine) need
    > to be returned to Canon for calibration before their PD AF works within
    > Canon's specification. I don't know if the defect rate is very different for
    > that model compared to others, or it's just that the 450D has become
    > renowned for it.


    Some of Sony's cheaper DSLRs also seem often to show AF calibration
    problems when used with very critical lenses with very shallow depths
    of field. It could be argued that Sony expect people buying such
    critical and expensive lenses to be using them with more expensive
    camera bodies. The kind of small AF errors which show up with very
    critical lenses at their extremes won't be noticeable with kit zoom
    lenses. The depth of field will simply always swallow them.

    It wouldn't be surprising if other camera makers spend a little less
    care in calibrating the AF in their less expensive models for the same
    reasons. Fortunately on the Sony alpha models the trimming screws
    which adjust the distance and orientation of the AF sensor plane are
    externally accessible and can be trimmed by owners with the technical
    skills. Some of those who have done so claim to be able with care to
    trim to greater AF precision than you often get by sending the
    camera back to the maker for calibration.

    That's why "have you got accessible AF trimming screws?" is one of
    the questions I ask of a new DSLR which wants me to buy it :)

    --
    Chris Malcolm
     
    Chris Malcolm, Sep 27, 2009
    #15
  16. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, John Navas
    <> wrote:

    > That's all speculation, and it doesn't take into consideration such
    > critical factors as the effectiveness of the focusing algorithms, the
    > data they have on the systems*, the speed and power of the focusing
    > motors, the masses they need to move, and the distance they need to move
    > it. As we say in computers, GIGO.
    >
    > * An advantage of a non-interchangeable lens camera is that the focusing
    > system can know exactly how the entire focusing system behaves. An
    > interchangeable lens system (SLR) inevitably has _less_ information
    > available.


    that's wrong. interchangeable lenses contain a rom chip that holds all
    of the parameters of the given lens so that the focusing system knows
    how to properly control it.

    in addition to the obvious data such as focal length and f/stop are the
    ballistics of the motor and/or gearing, so the camera can accurately
    determine how much to turn the motor.

    either system can have all the necessary information. there is no
    advantage to a fixed lens camera.

    > >but it's very
    > >surprising if it works better than the phase-based system used in DSLRs.

    >
    > Both contrast and phase based systems can be made to work very well in
    > practice, and it's silly and pointless to make sweeping claims about one
    > being "better" than the other.


    although both can work well, real world cameras that exist today show
    that the best phase detect systems outperform the best contrast detect
    systems. maybe one day that will change, but *today* that's how it is.
     
    nospam, Sep 28, 2009
    #16
  17. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, John Navas
    <> wrote:

    > >> * An advantage of a non-interchangeable lens camera is that the focusing
    > >> system can know exactly how the entire focusing system behaves. An
    > >> interchangeable lens system (SLR) inevitably has _less_ information
    > >> available.

    > >
    > >that's wrong. interchangeable lenses contain a rom chip that holds all
    > >of the parameters of the given lens so that the focusing system knows
    > >how to properly control it.

    >
    > A few parameters, yes, but far from all, whereas the non-interchangeable
    > lens camera does have _all_ the data.


    there is nothing precluding having all the data in an interchangeable
    lens, nor is there any guarantee that a fixed lens camera will have all
    the data.

    it is entirely possible that an interchangeable lens having *more* data
    than a fixed lens system, or it may have the same or less data. unless
    you have specifics of a given pair of products (which you don't), no
    conclusion can be made.

    > >either system can have all the necessary information. there is no
    > >advantage to a fixed lens camera.

    >
    > Simply not true.


    just the opposite, no many how many times you try to claim otherwise.
    where have i read that line before?

    > >> Both contrast and phase based systems can be made to work very well in
    > >> practice, and it's silly and pointless to make sweeping claims about one
    > >> being "better" than the other.

    > >
    > >although both can work well, real world cameras that exist today show
    > >that the best phase detect systems outperform the best contrast detect
    > >systems. maybe one day that will change, but *today* that's how it is.

    >
    > Again, simply not true, not to mention childish and pointless.
    > Do you also brag continually about the length of your manhood? ;)


    nice attempt at a diversion but that won't cut it. and i'm not the one
    with the 'twelve inches behind the camera' in his sig.
     
    nospam, Sep 28, 2009
    #17
  18. RichA

    nospam Guest

    Re: Panasonic's contrast focusing puts them miles ahead of any competition

    In article <>, John Navas
    <> wrote:

    > >> A few parameters, yes, but far from all, whereas the non-interchangeable
    > >> lens camera does have _all_ the data.

    > >
    > >there is nothing precluding having all the data in an interchangeable
    > >lens,

    >
    > Speculation is meaningless.
    > I'm only interested in real world implementations.


    and that's *exactly* why i said that absent a particular pair of
    products and an analysis of what data is *actually there* (especially
    since there's no defined list of what 'all the data' actually
    includes), no conclusion can be made. anything else is speculation.

    > >nor is there any guarantee that a fixed lens camera will have all
    > >the data.

    >
    > On the contrary -- it's built into the system.


    and it's built into the interchangeable lens.
     
    nospam, Sep 29, 2009
    #18
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