Reason for so many focus errors we see today?

Discussion in 'Digital Photography' started by RichA, Jun 23, 2009.

  1. RichA

    RichA Guest

    Plastic? Thermal expansion of plastic is much greater than metal and
    it could very well be why we are seeing focus issues that need "lens
    re-calibration" at service depots or that we see the need for in-
    camera focus fine-tuning. Even cameras and lenses that appear to be
    metal today may have plastic cells holding lenses, components in
    cameras. The cameras are produced in a control temp environment but
    that isn't real life use where temps can vary by 10's of degrees. I
    don't remember all metal AF SLRs needing focus fine-tuning (or having
    that facility) in the film days.
    RichA, Jun 23, 2009
    #1
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  2. RichA

    Pete D Guest

    "RichA" <> wrote in message
    news:...
    > Plastic? Thermal expansion of plastic is much greater than metal and
    > it could very well be why we are seeing focus issues that need "lens
    > re-calibration" at service depots or that we see the need for in-
    > camera focus fine-tuning. Even cameras and lenses that appear to be
    > metal today may have plastic cells holding lenses, components in
    > cameras. The cameras are produced in a control temp environment but
    > that isn't real life use where temps can vary by 10's of degrees. I
    > don't remember all metal AF SLRs needing focus fine-tuning (or having
    > that facility) in the film days.


    You mean like with Canon D1's and L glass, cos they all have this problem?

    Sometimes Rich even I think you are an idiot.
    Pete D, Jun 23, 2009
    #2
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  3. RichA

    Doug Jewell Guest

    RichA wrote:
    > Plastic? Thermal expansion of plastic is much greater than metal and

    Bzzt, wrong.
    Coefficients of Linear thermal expansion (10^-6 m/m/C):
    Aluminium 23.1
    Magnesium 26
    Brass 19
    Stainless Steel 17
    Steel 11-13
    Glass reinforced Polycarbonate 22
    So there's not a lot in it.

    > it could very well be why we are seeing focus issues that need "lens
    > re-calibration" at service depots or that we see the need for in-
    > camera focus fine-tuning. Even cameras and lenses that appear to be
    > metal today may have plastic cells holding lenses, components in
    > cameras. The cameras are produced in a control temp environment but
    > that isn't real life use where temps can vary by 10's of degrees. I

    To put expansion in perspective, a 30 degree C change in
    temp on a 300mm lens made of Magnesium would be a mere
    0.2mm. Every lens I've ever seen has that much play in it's
    movement if not more.

    > don't remember all metal AF SLRs needing focus fine-tuning (or having
    > that facility) in the film days.

    Because of the lower resolution of the sensor it wasn't as
    critical. Consider that a typical 35mm frame of film can
    resolve the equivalent of maybe 12-15MP. Modern DSLR's will
    cram 12-15MP on a sensor that has half the surface area, or
    are putting 24MP onto the 35mm frame. Because of this higher
    resolution they require more critical focus from the lens,
    and so errors that have always existed are now noticed.




    --
    Don't blame me - I didn't vote for Kevin Rudd or Anna Bligh!
    Doug Jewell, Jun 23, 2009
    #3
  4. RichA

    Don Stauffer Guest

    RichA wrote:
    > Plastic? Thermal expansion of plastic is much greater than metal and
    > it could very well be why we are seeing focus issues that need "lens
    > re-calibration" at service depots or that we see the need for in-
    > camera focus fine-tuning. Even cameras and lenses that appear to be
    > metal today may have plastic cells holding lenses, components in
    > cameras. The cameras are produced in a control temp environment but
    > that isn't real life use where temps can vary by 10's of degrees. I
    > don't remember all metal AF SLRs needing focus fine-tuning (or having
    > that facility) in the film days.



    I can see that in open loop focusing, where you estimate the distance
    and dial that distance on lens. However, in any closed loop operation
    that source of error would not lead to a focus error. Also, there are a
    some plastics that have a thermal expansion less than many metals. So
    one cannot use generalities on this.
    Don Stauffer, Jun 23, 2009
    #4
  5. RichA

    Nobody Guest

    "Doug Jewell" <> wrote in message
    news:4a40c593$0$2602$...
    > > don't remember all metal AF SLRs needing focus fine-tuning (or having
    >> that facility) in the film days.

    > Because of the lower resolution of the sensor it wasn't as critical.
    > Consider that a typical 35mm frame of film can resolve the equivalent of
    > maybe 12-15MP. Modern DSLR's will cram 12-15MP on a sensor that has half
    > the surface area, or are putting 24MP onto the 35mm frame. Because of this
    > higher resolution they require more critical focus from the lens, and so
    > errors that have always existed are now noticed.
    >

    How thick is a film emulsion, versus the sensor plane of a chip. I would
    hazard to suggest a CCD/CMOS is more critical than film.
    Nobody, Jun 23, 2009
    #5
  6. RichA

    Charles Guest

    "John O'Flaherty" <> wrote in message
    news:...
    > On Tue, 23 Jun 2009 08:56:14 -0500, Don Stauffer
    > <> wrote:



    > Focusing with a phase contrast system isn't closed loop with regard
    > to the picture sensor, since it uses a separate, simple sensor array
    > for focusing. Thus the focus system can get out of calibration.


    Agreed about the separate sensor array. However, the phase system (at least
    on some cameras) seems to be a hybrid servo (open loop for fast response,
    then switches to closed loop for the final tweak ... that's where the
    hunting comes in). There was a protracted debate about this on one Canon
    forum and it never was resolved, since some of the information is
    proprietary.
    Charles, Jun 23, 2009
    #6
  7. In rec.photo.digital.slr-systems John O'Flaherty <> wrote:
    > On Tue, 23 Jun 2009 08:56:14 -0500, Don Stauffer
    > <> wrote:


    >>RichA wrote:
    >>> Plastic? Thermal expansion of plastic is much greater than metal and
    >>> it could very well be why we are seeing focus issues that need "lens
    >>> re-calibration" at service depots or that we see the need for in-
    >>> camera focus fine-tuning. Even cameras and lenses that appear to be
    >>> metal today may have plastic cells holding lenses, components in
    >>> cameras. The cameras are produced in a control temp environment but
    >>> that isn't real life use where temps can vary by 10's of degrees. I
    >>> don't remember all metal AF SLRs needing focus fine-tuning (or having
    >>> that facility) in the film days.

    >>
    >>
    >>I can see that in open loop focusing, where you estimate the distance
    >>and dial that distance on lens. However, in any closed loop operation
    >>that source of error would not lead to a focus error. Also, there are a
    >>some plastics that have a thermal expansion less than many metals. So
    >>one cannot use generalities on this.


    > Focusing with a phase contrast system isn't closed loop with regard
    > to the picture sensor, since it uses a separate, simple sensor array
    > for focusing. Thus the focus system can get out of calibration.


    True, but thermal expansion in the lens *is* within the AF closed
    loop, so that particular problem won't give rise to focus errors in an
    AF system.

    --
    Chris Malcolm
    Chris Malcolm, Jun 23, 2009
    #7
  8. John Navas wrote:
    []
    > It's the dark side (secret) of phase detection. Fast focusing
    > inevitably involves some focus error, since it's predictive, and
    > affected by lens errors. To fix that requires fine tuning, which can
    > slow down focusing considerably. The reason more people don't notice
    > is that it's lens sensitive, so focusing with a good lens, as in the
    > case of most reviews, may still be fast. The issue doesn't exist for
    > contrast detection, which is now fast enough for speed not to be an
    > issue.


    But, contrast detection relies on detecting a maximum, with no information
    about what direction the focus system should be driven. With phase
    detection you are seeking a zero, and the sensor output tell you which way
    to drive the focus, making a very fast, one-shot, open-loop movement
    possible. Iterate further /i/f there is any need. On the other hand,
    detecting a maximum can be quite a lot slower as you need to seek on
    either side of the maximum and make a best guess as to the peak. Swings
    and roundabouts for both systems.

    David
    David J Taylor, Jun 24, 2009
    #8
  9. RichA

    Rich Guest

    On Jun 23, 8:07 am, Doug Jewell <> wrote:
    > RichA wrote:
    > > Plastic?  Thermal expansion of plastic is much greater than metal and

    >
    > Bzzt, wrong.
    > Coefficients of Linear thermal expansion (10^-6 m/m/C):
    > Aluminium 23.1
    > Magnesium 26
    > Brass 19
    > Stainless Steel 17
    > Steel 11-13
    > Glass reinforced Polycarbonate 22
    > So there's not a lot in it.


    That is for glass-filled. Non-glass filled is three times that. Not
    all polycarbs are glass-filled. It is
    also the differential of expansion between two different materials
    that is the problem. All aluminum and maybe all plasic on their own
    might be ok, but combined it causes problems, like the binding of lens
    elements when temperatures drop.
    Rich, Jun 24, 2009
    #9
  10. In rec.photo.digital.slr-systems John Navas <> wrote:
    > On 23 Jun 2009 20:38:58 GMT, Chris Malcolm <> wrote
    > in <>:


    >>In rec.photo.digital.slr-systems John O'Flaherty <> wrote:


    >>> Focusing with a phase contrast system isn't closed loop with regard
    >>> to the picture sensor, since it uses a separate, simple sensor array
    >>> for focusing. Thus the focus system can get out of calibration.

    >>
    >>True, but thermal expansion in the lens *is* within the AF closed
    >>loop, so that particular problem won't give rise to focus errors in an
    >>AF system.


    > What closed loop? Many (most?) phase detection autofocus is open loop.


    Most is open loop with respect to focus on the image sensor, and
    closed loop for at least the final approach on the AF sensor. There's
    a lot of misunderstanding and misinformation on this topic. Try the
    experiment of locking focus with a half press on something near when a
    big slow focusing lens is at infinity. Then complete the press, and
    after the lens has started to move, but before it has stopped, remove
    the thing it's focussed on from the view of the AF sensor. If the lens
    runs past that point without stopping then it's a closed loop system
    whose terminating condition has not been found. If it's a predictive
    system it will stop focused on the distance the object was earlier
    found to be at, even though it's no longer there.

    --
    Chris Malcolm
    Chris Malcolm, Jun 24, 2009
    #10
  11. John Navas <> wrote:

    > Fast focusing
    > inevitably involves some focus error, since it's predictive, and
    > affected by lens errors.


    Please explain how lens errors are affecting focus detection in
    DSLRs, but not when using contrast detection.

    > To fix that requires fine tuning, which can
    > slow down focusing considerably. The reason more people don't notice is
    > that it's lens sensitive, so focusing with a good lens, as in the case
    > of most reviews, may still be fast. The issue doesn't exist for
    > contrast detection, which is now fast enough for speed not to be an
    > issue.


    Sure, and P&S cameras focus near instantly, too. Pull the
    other one.

    -Wolfgang
    Wolfgang Weisselberg, Jun 24, 2009
    #11
  12. RichA

    Don Stauffer Guest

    John O'Flaherty wrote:
    > On Tue, 23 Jun 2009 08:56:14 -0500, Don Stauffer
    > <> wrote:
    >
    >> RichA wrote:
    >>> Plastic? Thermal expansion of plastic is much greater than metal and
    >>> it could very well be why we are seeing focus issues that need "lens
    >>> re-calibration" at service depots or that we see the need for in-
    >>> camera focus fine-tuning. Even cameras and lenses that appear to be
    >>> metal today may have plastic cells holding lenses, components in
    >>> cameras. The cameras are produced in a control temp environment but
    >>> that isn't real life use where temps can vary by 10's of degrees. I
    >>> don't remember all metal AF SLRs needing focus fine-tuning (or having
    >>> that facility) in the film days.

    >>
    >> I can see that in open loop focusing, where you estimate the distance
    >> and dial that distance on lens. However, in any closed loop operation
    >> that source of error would not lead to a focus error. Also, there are a
    >> some plastics that have a thermal expansion less than many metals. So
    >> one cannot use generalities on this.

    >
    > Focusing with a phase contrast system isn't closed loop with regard
    > to the picture sensor, since it uses a separate, simple sensor array
    > for focusing. Thus the focus system can get out of calibration.


    I was under the impression that the OP was talking about lens cell
    materials. The structure holding the image chip and the focusing chip
    is in the body of the camera, so a movement of something within the lens
    itself should affect both chips the same, shouldn't it?
    Don Stauffer, Jun 24, 2009
    #12
  13. In rec.photo.digital.slr-systems John O'Flaherty <> wrote:
    > On Wed, 24 Jun 2009 09:04:14 -0500, Don Stauffer
    > <> wrote:


    >>John O'Flaherty wrote:
    >>> On Tue, 23 Jun 2009 08:56:14 -0500, Don Stauffer
    >>> <> wrote:
    >>>
    >>>> RichA wrote:
    >>>>> Plastic? Thermal expansion of plastic is much greater than metal and
    >>>>> it could very well be why we are seeing focus issues that need "lens
    >>>>> re-calibration" at service depots or that we see the need for in-
    >>>>> camera focus fine-tuning. Even cameras and lenses that appear to be
    >>>>> metal today may have plastic cells holding lenses, components in
    >>>>> cameras. The cameras are produced in a control temp environment but
    >>>>> that isn't real life use where temps can vary by 10's of degrees. I
    >>>>> don't remember all metal AF SLRs needing focus fine-tuning (or having
    >>>>> that facility) in the film days.
    >>>>
    >>>> I can see that in open loop focusing, where you estimate the distance
    >>>> and dial that distance on lens. However, in any closed loop operation
    >>>> that source of error would not lead to a focus error. Also, there are a
    >>>> some plastics that have a thermal expansion less than many metals. So
    >>>> one cannot use generalities on this.
    >>>
    >>> Focusing with a phase contrast system isn't closed loop with regard
    >>> to the picture sensor, since it uses a separate, simple sensor array
    >>> for focusing. Thus the focus system can get out of calibration.

    >>
    >>I was under the impression that the OP was talking about lens cell
    >>materials. The structure holding the image chip and the focusing chip
    >>is in the body of the camera, so a movement of something within the lens
    >>itself should affect both chips the same, shouldn't it?


    > My impression of the o.p. was that it was about the camera in general,
    > anything that could require recalibration of focus. Anyway, I think a
    > phase system is open loop in general, since it moves the lens focus in
    > a direction and amount indicated by the comparison of two adjacent
    > sensor strips (at least for a first pass). So, maybe changes in the
    > lens itself will affect the accuracy.


    I think rather than open loop "in general" you mean "at first". It's
    difficult getting at the technical details of phase detection
    autofocus, since it's both highly technical, and at least in some
    cases the details are regarded as a trade secret by the
    manufacturer. However, having read the workshop repair manual for one
    set of Canon lenses, which in passing mentioned various aspects of
    autofocus as relevent to a service engineer, the impression I was left
    with was that in those particular lenses, which were made for specially
    fast focusing, what happens is as follows.

    The AF phase detection makes a first measurement of the direction
    and approximate distance to focus. The focus motor control then sets
    up the parameters for the focus movement. If the distance is long
    enough to warrant it this is a four phase movement.

    The first phase is an acceleration of the lens up to its maximum speed
    of focus travel. This is terminated automatically when the motor is
    spinning at maximum speed, and the second phase begun. The second
    phase travels at maximum speed until it gets to the deceleration
    position, at which point it automatically starts the third phase, the
    deceleration ramp down to the final focus approach speed. That final
    fourth phase approach speed is slow enough to allow a closed loop
    approach to focus detection by the AF sensor which given the inertia
    of the lens etc.. can be stopped close enough to exact focus that
    there will be no overshoot.

    If the lens overshot the focus point it would have to
    reverse. Reversal of direction is expensive in time, so like a car
    approaching a stop light it decelerates at a speed at which it can
    reliably stop close enough to the line. In the case of these lenses
    "close enough" is a permissible error parameter previously read by the
    camera from a table in ROM in the lens, and which is alterable by
    service engineers in the lens focus calibration procedure. That
    parameter may also be adjusted by the camera depending on the chosen
    aperture. In that way smaller apertures can focus the lens a bit
    faster. That parameter may also incorporate an early stop factor to
    take account for the delays, inertia, etc. in the system, which mean
    that it will always stop a little bit further on than where it was
    when the software loop decided to stop the motor.

    When the deceleration phase finishes the lens is now not quite at the
    required focus point, and moving slowly enough to operate in closed
    loop manner, closed on good enough focus detection by the AF
    sensor. That'a the fourth final closed loop phase. It drives on at
    that speed reading the sensor, and stops when it detects near enough
    focus. Of course sometimes it won't detect focus, because the squirrel
    may have moved away or the light changed enough to lose the necessary
    contrast in the sensor while the lens was moving. So there is also a
    timing watchdog to terminate this loop if it goes on for too
    long. Other lenses/AF systems don't use a watchdog and simply keep
    running the lens until it hits the end stop. Simpler, but slower.
    Termination on the final focus approach loop on a focus find failure
    condition will automatically initiate another complete focus from
    scratch loop. This is how "hunting" happens, and whether it runs from
    end to end of complete focus travel, or dithers about the focus point,
    depends on whether the system uses timer watchdog or end stop failure,
    and what kind of outer loop control system is operating.

    Of course if the camera is doing a more complicated kind of focus such
    as predictive focus of a moving object, or approaching a compromise
    focus between the readings from a number of previously selected AF
    sensors, a more complicated procedure is used. I'm describing here the
    simplest long distance high speed AF procedure. If the focus point is
    close to where the lens is of course it will only use the final
    approach phase.

    The manual also made it clear that not all Canon lenses were
    sophisticated enough to use this sophisticated long distance high
    speed focus method. Simpler modelds have only a single speed focus
    system.

    I also get the impression that there is another two speed AF system
    used by some lens/body combinations, where the high speed checks the
    AF sensor only every several motor steps, and when it gets near slows
    down to checking every step.

    I think it's an oversimplification to talk of THE phase detection AF
    system of DSLRs, since in the search for highest speed and highest
    accuracy the camera makers have kept improving the sophistication of
    both their AF sensors and the focus control loops using them. In some
    cases we've seen a camera maker offer a camera model software upgrade
    which has improved focus performance not by fixing a bug but by
    introducing a more sophisticated control system.

    There are a number of different phase detection AF systems out there,
    of different levels of sophistication and accuracy. Some, I suspect
    these days at least most, always operate a closed loop approach of
    monitoring the AF sensor during the final approach to the focus point.

    Some camera makers have caused confusion on this question of whether
    their DSLR AF systems are open or closed loop by describing them as
    open loop because the closed loop they operate is closed around the AF
    sensor and not the image sensor, whereas their compact cameras operate
    a loop closed around the image sensor. In terms of control theory it's
    technically correct to describe DSLR phase detection autofocus systems
    as open loop, because they don't close the loop by measuring the
    achievement of the purpose of the system, which is an image focused on
    the image sensor. Instead they close the loop around the proxy of the
    AF sensor. Hence all the focus calibration problems of DSLR autofocus.

    Unfortunately that technically correct description of DSLR autofocus
    as "open loop" without qualification has misled a lot of camera users
    unfamiliar with the technicalities of control systems theory into
    supposing that that "open loop" means that no DSLRs use the AF sensor
    in a closed loop fashion.

    --
    Chris Malcolm
    Chris Malcolm, Jun 25, 2009
    #13
  14. RichA

    Wilba Guest

    Chris Malcolm wrote:

    > I think rather than open loop "in general" you mean "at first". It's
    > difficult getting at the technical details of phase detection
    > autofocus, since it's both highly technical, and at least in some
    > cases the details are regarded as a trade secret by the
    > manufacturer. However, having read the workshop repair manual for one
    > set of Canon lenses, which in passing mentioned various aspects of
    > autofocus as relevent to a service engineer, the impression I was left
    > with was that in those particular lenses, which were made for specially
    > fast focusing, what happens is as follows.
    >
    > The AF phase detection makes a first measurement of the direction
    > and approximate distance to focus. The focus motor control then sets
    > up the parameters for the focus movement. If the distance is long
    > enough to warrant it this is a four phase movement.
    >
    > The first phase is an acceleration of the lens up to its maximum speed
    > of focus travel. This is terminated automatically when the motor is
    > spinning at maximum speed, and the second phase begun. The second
    > phase travels at maximum speed until it gets to the deceleration
    > position, at which point it automatically starts the third phase, the
    > deceleration ramp down to the final focus approach speed. That final
    > fourth phase approach speed is slow enough to allow a closed loop
    > approach to focus detection by the AF sensor which given the inertia
    > of the lens etc.. can be stopped close enough to exact focus that
    > there will be no overshoot.
    >
    > If the lens overshot the focus point it would have to
    > reverse. Reversal of direction is expensive in time, so like a car
    > approaching a stop light it decelerates at a speed at which it can
    > reliably stop close enough to the line. In the case of these lenses
    > "close enough" is a permissible error parameter previously read by the
    > camera from a table in ROM in the lens, and which is alterable by
    > service engineers in the lens focus calibration procedure. That
    > parameter may also be adjusted by the camera depending on the chosen
    > aperture. In that way smaller apertures can focus the lens a bit
    > faster. That parameter may also incorporate an early stop factor to
    > take account for the delays, inertia, etc. in the system, which mean
    > that it will always stop a little bit further on than where it was
    > when the software loop decided to stop the motor.
    >
    > When the deceleration phase finishes the lens is now not quite at the
    > required focus point, and moving slowly enough to operate in closed
    > loop manner, closed on good enough focus detection by the AF
    > sensor. That'a the fourth final closed loop phase. It drives on at
    > that speed reading the sensor, and stops when it detects near enough
    > focus. Of course sometimes it won't detect focus, because the squirrel
    > may have moved away or the light changed enough to lose the necessary
    > contrast in the sensor while the lens was moving. So there is also a
    > timing watchdog to terminate this loop if it goes on for too
    > long. Other lenses/AF systems don't use a watchdog and simply keep
    > running the lens until it hits the end stop. Simpler, but slower.
    > Termination on the final focus approach loop on a focus find failure
    > condition will automatically initiate another complete focus from
    > scratch loop. This is how "hunting" happens, and whether it runs from
    > end to end of complete focus travel, or dithers about the focus point,
    > depends on whether the system uses timer watchdog or end stop failure,
    > and what kind of outer loop control system is operating.
    >
    > Of course if the camera is doing a more complicated kind of focus such
    > as predictive focus of a moving object, or approaching a compromise
    > focus between the readings from a number of previously selected AF
    > sensors, a more complicated procedure is used. I'm describing here the
    > simplest long distance high speed AF procedure. If the focus point is
    > close to where the lens is of course it will only use the final
    > approach phase.
    >
    > The manual also made it clear that not all Canon lenses were
    > sophisticated enough to use this sophisticated long distance high
    > speed focus method. Simpler modelds have only a single speed focus
    > system.
    >
    > I also get the impression that there is another two speed AF system
    > used by some lens/body combinations, where the high speed checks the
    > AF sensor only every several motor steps, and when it gets near slows
    > down to checking every step.
    >
    > I think it's an oversimplification to talk of THE phase detection AF
    > system of DSLRs, since in the search for highest speed and highest
    > accuracy the camera makers have kept improving the sophistication of
    > both their AF sensors and the focus control loops using them. In some
    > cases we've seen a camera maker offer a camera model software upgrade
    > which has improved focus performance not by fixing a bug but by
    > introducing a more sophisticated control system.
    >
    > There are a number of different phase detection AF systems out there,
    > of different levels of sophistication and accuracy. Some, I suspect
    > these days at least most, always operate a closed loop approach of
    > monitoring the AF sensor during the final approach to the focus point.
    >
    > Some camera makers have caused confusion on this question of whether
    > their DSLR AF systems are open or closed loop by describing them as
    > open loop because the closed loop they operate is closed around the AF
    > sensor and not the image sensor, whereas their compact cameras operate
    > a loop closed around the image sensor. In terms of control theory it's
    > technically correct to describe DSLR phase detection autofocus systems
    > as open loop, because they don't close the loop by measuring the
    > achievement of the purpose of the system, which is an image focused on
    > the image sensor. Instead they close the loop around the proxy of the
    > AF sensor. Hence all the focus calibration problems of DSLR autofocus.
    >
    > Unfortunately that technically correct description of DSLR autofocus
    > as "open loop" without qualification has misled a lot of camera users
    > unfamiliar with the technicalities of control systems theory into
    > supposing that that "open loop" means that no DSLRs use the AF sensor
    > in a closed loop fashion.


    Thanks for that Chris. There's a lot of stuff there I didn't know.

    Is that "workshop repair manual" available online? I have a copy of the "EF
    50mm 1.8, 28mm 2.8, and 15mm 2.8 Service Manual", but AFAIK that doesn't go
    into the operation like you described.
    Wilba, Jun 25, 2009
    #14
  15. RichA

    Don Stauffer Guest

    Chris Malcolm wrote:

    >
    > I think rather than open loop "in general" you mean "at first". It's
    > difficult getting at the technical details of phase detection
    > autofocus, since it's both highly technical, and at least in some
    > cases the details are regarded as a trade secret by the
    > manufacturer. However, having read the workshop repair manual for one
    > set of Canon lenses, which in passing mentioned various aspects of
    > autofocus as relevent to a service engineer, the impression I was left
    > with was that in those particular lenses, which were made for specially
    > fast focusing, what happens is as follows.
    >

    There was a big patent fight between Honeywell and someone (I forget who
    right at the moment. I followed the case because I worked for Honeywell
    at the time. The lawyers even gave a noontime seminar one day for folks
    interested in the case). It was over the details of that particular
    autofocus method. The material disclosed in court is voluminous, but is
    at least part of public record.
    Don Stauffer, Jun 25, 2009
    #15
  16. RichA

    nospam Guest

    In article <4a437ae0$0$1331$>, Don Stauffer
    <> wrote:

    > There was a big patent fight between Honeywell and someone (I forget who
    > right at the moment. I followed the case because I worked for Honeywell
    > at the time. The lawyers even gave a noontime seminar one day for folks
    > interested in the case). It was over the details of that particular
    > autofocus method. The material disclosed in court is voluminous, but is
    > at least part of public record.


    minolta.
    nospam, Jun 25, 2009
    #16
  17. In article <4a42325f$0$48219$>, Don Stauffer
    <> writes
    >
    >I was under the impression that the OP was talking about lens cell
    >materials.


    No, the OP was continuing a decade long rant about something he has
    little knowledge of but finds it a convenient subject to troll with.
    --
    Kennedy
    Yes, Socrates himself is particularly missed;
    A lovely little thinker, but a bugger when he's pissed.
    Python Philosophers (replace 'nospam' with 'kennedym' when replying)
    Kennedy McEwen, Jun 25, 2009
    #17
  18. RichA

    Lloyd W. Guest

    Re: How To Detect Snapshooters from Photographers

    "Truer Dat" <> wrote in message
    news:...

    [Demented ramblings deleted]
    >
    > The list goes on and on. All you have to do is stop to realize why they
    > NEED those camera features. Each and every time it points directly to them
    > being nothing but a talentless-hack, point and shoot, snapshooter; or
    > total
    > gear-head, not even a lowly snapshooter; crippled and dependent on their
    > automated point and shoot cameras.
    >


    The list may go on and on but so do you. This smells like that pompous
    blowhard, Semi-Yawning from the "Anything for a Perfect Shot" thread.

    LloydW.
    Lloyd W., Jun 25, 2009
    #18
  19. Re: How To Detect Snapshooters from Photographers

    Please don't feed the pests.

    --
    lsmft

    "Andre, a simple peasant, had only one thing on his mind as he crept
    along the East wall: 'Andre creep ... Andre creep ... Andre creep'."
    John McWilliams, Jun 25, 2009
    #19
  20. RichA

    John Navas Guest

    Re: How To Detect Snapshooters from Photographers

    On Thu, 25 Jun 2009 14:17:43 -0500, Ron Hunter <>
    wrote in <>:

    >Truer Dat wrote:
    >> On Tue, 23 Jun 2009 03:50:05 -0700 (PDT), RichA <>
    >> wrote:
    >>
    >>[HUGE SNIP]
    >>

    >I think you will find that the focusing systems on modern cameras are
    >faster, and more accurate than most humans. Now if you have something
    >like a case where something large is closer than your subject, the
    >camera can be confused, and the photographer can compensate. I always
    >take note of this situation, and allow the camera to focus on my
    >subject, then lock the focus, and recompose the shot.


    Please trim huge quotes to just a relevant portion, not the whole thing.
    Thanks.

    --
    Best regards,
    John (Panasonic DMC-FZ28, and several others)
    John Navas, Jun 25, 2009
    #20
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