Re: Help please - Optical image stabilization with telephoto adapter?

Discussion in 'Digital Photography' started by David J Taylor, May 15, 2008.

  1. Bob Cunningham wrote:
    > Some cameras, like Canon G9 and Canon S5 IS, have provision
    > for attaching a telephoto adapter or a wide-angle adapter.
    >
    > If the camera has optical image stabilization, as do those
    > two cameras, will that stabilization still be effective with
    > the added zoom adapter?


    Yes.

    David
     
    David J Taylor, May 15, 2008
    #1
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  2. Paul Allen wrote:
    > On Thu, 15 May 2008 10:02:48 +0000, David J Taylor wrote:
    >
    >> Bob Cunningham wrote:
    >>> Some cameras, like Canon G9 and Canon S5 IS, have provision for
    >>> attaching a telephoto adapter or a wide-angle adapter.
    >>>
    >>> If the camera has optical image stabilization, as do those two
    >>> cameras, will that stabilization still be effective with the added
    >>> zoom adapter?

    >>
    >> Yes.

    >
    > What David meant was that a zoom adapter will have no effect on the
    > proper functioning of image stabilization. He should have added that
    > any shaking that gets past the stabilizer will be magnified by the
    > added zoom.
    >
    > I use a tripod when I care about my pictures, but that's just me. :)
    >
    > Paul Allen


    I don't carry a tripod around in my pocket, or on a field trip or visit to
    the races. I find that Image Stabilised lenses suit my needs admirably.

    When I want a much longer exposure I just find some natural object against
    which I can brace the camera.

    David
     
    David J Taylor, May 18, 2008
    #2
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  3. "David J Taylor" <-this-bit.nor-this-bit.co.uk> writes:
    >Bob Cunningham wrote:
    >> Some cameras, like Canon G9 and Canon S5 IS, have provision
    >> for attaching a telephoto adapter or a wide-angle adapter.


    >> If the camera has optical image stabilization, as do those
    >> two cameras, will that stabilization still be effective with
    >> the added zoom adapter?


    >Yes.


    Are you certain of that? It's not what I'd expect, though I don't have
    such a camera to test.

    Here's my reasoning: Suppose the adapter is a 2X telephoto adapter.
    Suppose your hand holding the camera shakes +- 1 degree in one axis.
    Because of the angular magnification of the telephoto adapter, the main
    lens of the camera, looking through the adapter, sees +- 2 degrees of
    angular motion, not 1 degree. The camera's acceleration sensors
    detect the camera shake and move an internal lens element (or prism) by
    the appropriate amount to cancel 1 degree of shake - not 2 degrees. To
    properly cancel the larger apparent shake, the stabilization system
    needs to double the gain of the system, in terms of compensation per
    degree of shake motion.

    The anti-shake system will automatically adjust its gain as required as
    the main lens changes focal length via zooming, but it doesn't know that
    the tele or wideangle converter is there.

    Now, if the camera has a menu item to tell the camera that the tele or
    wideangle adapter is currently mounted, ignore what I said above - the
    camera does have the required information to set the antishake system
    properly.

    Also, if the magnifiying device is rigidly mounted and only the camera
    shakes, then the stabilization would still work correctly. This might
    be the case if you are handholding the camera at the eyepiece of a
    telescope or microscope, shooting through the eyepiece. But not when
    the camera and other optics are both shaking.

    Dave
     
    Dave Martindale, May 18, 2008
    #3
  4. Dave Martindale wrote:
    > "David J Taylor"
    > <-this-bit.nor-this-bit.co.uk> writes:
    >> Bob Cunningham wrote:
    >>> Some cameras, like Canon G9 and Canon S5 IS, have provision
    >>> for attaching a telephoto adapter or a wide-angle adapter.

    >
    >>> If the camera has optical image stabilization, as do those
    >>> two cameras, will that stabilization still be effective with
    >>> the added zoom adapter?

    >
    >> Yes.

    >
    > Are you certain of that? It's not what I'd expect, though I don't
    > have
    > such a camera to test.
    >
    > Here's my reasoning: Suppose the adapter is a 2X telephoto adapter.
    > Suppose your hand holding the camera shakes +- 1 degree in one axis.
    > Because of the angular magnification of the telephoto adapter, the
    > main
    > lens of the camera, looking through the adapter, sees +- 2 degrees of
    > angular motion, not 1 degree. The camera's acceleration sensors
    > detect the camera shake and move an internal lens element (or prism)
    > by
    > the appropriate amount to cancel 1 degree of shake - not 2 degrees.
    > To
    > properly cancel the larger apparent shake, the stabilization system
    > needs to double the gain of the system, in terms of compensation per
    > degree of shake motion.
    >
    > The anti-shake system will automatically adjust its gain as required
    > as
    > the main lens changes focal length via zooming, but it doesn't know
    > that
    > the tele or wideangle converter is there.
    >
    > Now, if the camera has a menu item to tell the camera that the tele or
    > wideangle adapter is currently mounted, ignore what I said above - the
    > camera does have the required information to set the antishake system
    > properly.
    >
    > Also, if the magnifiying device is rigidly mounted and only the camera
    > shakes, then the stabilization would still work correctly. This might
    > be the case if you are handholding the camera at the eyepiece of a
    > telescope or microscope, shooting through the eyepiece. But not when
    > the camera and other optics are both shaking.
    >
    > Dave


    Dave,

    Thanks for your input. I had been assuming that the magnification of the
    adaptor would not affect the stabilisation, and whilst I am still unsure
    about exactly what happens (in that isn't the stabilisation magnified by
    as much as the image?), I do accept that for best results you would need
    to tell the camera that the optical chain had changed via a menu. I note
    that the Panasonic FZ20, for example, has just such a menu item.

    Cheers,
    David
     
    David J Taylor, May 18, 2008
    #4
  5. David J Taylor

    Archibald Guest

    On Sun, 18 May 2008 15:52:42 -0700, Bob Cunningham
    <> wrote:

    >We need to keep in mind that the stabilization technique
    >used on a given camera may react to vertical and horizontal
    >movements only, so that angular movement of the longitudinal
    >lens axis could not be compensated. In a Wikipedia article
    >about image stabilization at http://tinyurl.com/5jm42k *, it
    >says in part
    >
    > In Nikon and Canon's implementation, it works by
    > using a floating lens element that is moved
    > orthogonally to the optical axis of the lens, using
    > electromagnets. The vibration signal which is
    > compensated for by the stabilizing lens element is
    > typically acquired using two piezoelectric angular
    > velocity sensors (often called gyroscopic sensors),
    > one to detect horizontal movement and the other to
    > detect vertical movement.
    >
    >In a review of the Canon G9 at
    >it says
    >
    > Lens-Shift type optical image stabilization system
    >
    >About the S5IS, it says at
    >http://www.dpreview.com/news/0705/07050703canons5is.asp
    >
    > Image stabilization Yes (Lens shift-type)
    >
    >To counter the angular motion that DM discussed, wouldn't
    >the system have to rotate the lens rather than just shift
    >it.


    Horizontal and vertical movement of the camera isn't going to blur
    images much, except for stuff that is close to the camera. So IS must
    be able to deal with angular movement, I think.

    Archibald
     
    Archibald, May 19, 2008
    #5
  6. Bob Cunningham wrote:
    []
    > To counter the angular motion that DM discussed, wouldn't
    > the system have to rotate the lens rather than just shift
    > it.


    Bob,

    The lens senses an angular motion, and then uses a shift of elements
    within the lens to produce an angular displacement of the image. If you
    like to look at it this way, a linear shift, at a finite distance, becomes
    an angular shift.

    Cheers,
    David
     
    David J Taylor, May 19, 2008
    #6
  7. David J Taylor <-this-bit.nor-this-bit.co.uk> wrote:
    > Dave Martindale wrote:
    >> "David J Taylor"
    >> <-this-bit.nor-this-bit.co.uk> writes:
    >>> Bob Cunningham wrote:
    >>>> Some cameras, like Canon G9 and Canon S5 IS, have provision
    >>>> for attaching a telephoto adapter or a wide-angle adapter.

    >>
    >>>> If the camera has optical image stabilization, as do those
    >>>> two cameras, will that stabilization still be effective with
    >>>> the added zoom adapter?

    >>
    >>> Yes.

    >>
    >> Are you certain of that? It's not what I'd expect, though I don't
    >> have
    >> such a camera to test.
    >>
    >> Here's my reasoning: Suppose the adapter is a 2X telephoto adapter.
    >> Suppose your hand holding the camera shakes +- 1 degree in one axis.
    >> Because of the angular magnification of the telephoto adapter, the
    >> main
    >> lens of the camera, looking through the adapter, sees +- 2 degrees of
    >> angular motion, not 1 degree. The camera's acceleration sensors
    >> detect the camera shake and move an internal lens element (or prism)
    >> by
    >> the appropriate amount to cancel 1 degree of shake - not 2 degrees.
    >> To
    >> properly cancel the larger apparent shake, the stabilization system
    >> needs to double the gain of the system, in terms of compensation per
    >> degree of shake motion.
    >>
    >> The anti-shake system will automatically adjust its gain as required
    >> as
    >> the main lens changes focal length via zooming, but it doesn't know
    >> that
    >> the tele or wideangle converter is there.
    >>
    >> Now, if the camera has a menu item to tell the camera that the tele or
    >> wideangle adapter is currently mounted, ignore what I said above - the
    >> camera does have the required information to set the antishake system
    >> properly.
    >>
    >> Also, if the magnifiying device is rigidly mounted and only the camera
    >> shakes, then the stabilization would still work correctly. This might
    >> be the case if you are handholding the camera at the eyepiece of a
    >> telescope or microscope, shooting through the eyepiece. But not when
    >> the camera and other optics are both shaking.
    >>
    >> Dave


    > Dave,


    > Thanks for your input. I had been assuming that the magnification of the
    > adaptor would not affect the stabilisation, and whilst I am still unsure
    > about exactly what happens (in that isn't the stabilisation magnified by
    > as much as the image?), I do accept that for best results you would need
    > to tell the camera that the optical chain had changed via a menu.


    Unless the IS system was adaptive, noting its over- and underestimates
    and adapting to cancel them out. I don't know if any camera maker uses
    such a system, but it's well understood how to do that well, and it
    automatically avoids the problems of being improperly informed.

    --
    Chris Malcolm DoD #205
    IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
    [http://www.dai.ed.ac.uk/homes/cam/]
     
    Chris Malcolm, May 19, 2008
    #7
  8. "David J Taylor" <-this-bit.nor-this-bit.co.uk> writes:

    >Dave,


    >Thanks for your input. I had been assuming that the magnification of the
    >adaptor would not affect the stabilisation, and whilst I am still unsure
    >about exactly what happens (in that isn't the stabilisation magnified by
    >as much as the image?), I do accept that for best results you would need
    >to tell the camera that the optical chain had changed via a menu. I note
    >that the Panasonic FZ20, for example, has just such a menu item.


    The stabilization happens behind the adaptor, so its effect is *not*
    magnified by the adaptor. But the effect of shake is magnified by a
    tele adaptor (and reduced by a wideangle one) because, to the camera, it
    looks like the world is shaking and the adaptor magnifies the apparent
    movement of the world.

    Dave
     
    Dave Martindale, May 20, 2008
    #8
  9. writes:

    >We need to keep in mind that the stabilization technique
    >used on a given camera may react to vertical and horizontal
    >movements only, so that angular movement of the longitudinal
    >lens axis could not be compensated.


    No, you're thinking of the wrong motions. Shake can cause the camera to
    move in any combination of 6 directions. There are 3 translation
    directions (left-right, up-down, near-far) and three angular motion
    diretions (pitch, yaw, and roll).

    Now, when you're using a long focal length lens (the usual place where
    stabilization is used), none of the translation motions are significant
    sources of blur. When the subject is much further away from the camera
    than the lens focal length, the small translational movements due to
    shake produce *much smaller* motions of the image on the film plane, not
    enough to worry about.

    It is the pitch and yaw rotations that matter most. The longer the
    focal length, the more apparent motion you get at the image plane for a
    small amount of rotation. And that's what lens stabilization systems
    correct for. They measure pitch and yaw *rotations* of the lens or
    camera body, and move a lens element or prism to shift the image an
    amount that approximately compensates for the shake-caused shift.

    In theory, you could also cause blur by roll around the camera optical
    axis, but (a) the amount of blur is not magnified by the lens focal
    length, and (b) there's no simple way to compensate for this anyway.
    So stabilized lenses do not correct for roll motion, to the best of my
    knowledge.

    >In a Wikipedia article
    >about image stabilization at http://tinyurl.com/5jm42k *, it
    >says in part


    > In Nikon and Canon's implementation, it works by
    > using a floating lens element that is moved
    > orthogonally to the optical axis of the lens, using
    > electromagnets. The vibration signal which is
    > compensated for by the stabilizing lens element is
    > typically acquired using two piezoelectric angular
    > velocity sensors (often called gyroscopic sensors),
    > one to detect horizontal movement and the other to
    > detect vertical movement.


    Right. It measures rotation around pitch and yaw axes, and compensates
    by Y and X-direction image shift.

    >In a review of the Canon G9 at
    >it says


    > Lens-Shift type optical image stabilization system


    Ditto. They say "lens shift" to distinguish it from the sensor-shifting
    systems in the bodies of some other manufacturers.

    >About the S5IS, it says at
    >http://www.dpreview.com/news/0705/07050703canons5is.asp


    > Image stabilization Yes (Lens shift-type)


    >To counter the angular motion that DM discussed, wouldn't
    >the system have to rotate the lens rather than just shift
    >it.


    But I wasn't talking about roll, I mean pitch and yaw.

    Dave
     
    Dave Martindale, May 20, 2008
    #9
  10. Chris Malcolm <> writes:

    >Unless the IS system was adaptive, noting its over- and underestimates
    >and adapting to cancel them out. I don't know if any camera maker uses
    >such a system, but it's well understood how to do that well, and it
    >automatically avoids the problems of being improperly informed.


    To do this, you'd need images fed back from the sensor to the
    stabilization system, plus some moderately powerful hardware to do the
    correlations. Doing this in a video camera would be relatively simple,
    since it's already producing 60 images per second. A P&S camera could
    do the same, likely at a somewhat slower frame rate.

    But a *film* camera cannot provide any image feedback at all, and most
    DSLRs provide only one image. A stabilization system for use on these
    cameras has to operate open-loop, without feedback, so that's what all
    the Canon and Nikon stabilized lenses must use. P&S cameras, and DSLRs
    with live LCD preview, *could* have IS with image feedback for
    self-tuning, but so far I haven't heard of one using it.

    Dave
     
    Dave Martindale, May 20, 2008
    #10
  11. "David J Taylor" <-this-bit.nor-this-bit.co.uk> writes:

    >I do accept that for best results you would need
    >to tell the camera that the optical chain had changed via a menu. I note
    >that the Panasonic FZ20, for example, has just such a menu item.


    I see that the Canon A720 *does* have a menu item for telling the camera
    that a particular Canon tele or wide adapter is mounted. So the A720's
    stabilization system would have the information needed to compensate for
    the magnification change. I wouldn't be surprised to find that the G9
    and S5, which are considerably more expensive cameras, have the same
    menu item as well.

    Dave
     
    Dave Martindale, May 20, 2008
    #11
  12. Dave Martindale wrote:
    > "David J Taylor"
    > <-this-bit.nor-this-bit.co.uk> writes:
    >
    >> Dave,

    >
    >> Thanks for your input. I had been assuming that the magnification
    >> of the adaptor would not affect the stabilisation, and whilst I am
    >> still unsure about exactly what happens (in that isn't the
    >> stabilisation magnified by as much as the image?), I do accept that
    >> for best results you would need to tell the camera that the optical
    >> chain had changed via a menu. I note that the Panasonic FZ20, for
    >> example, has just such a menu item.

    >
    > The stabilization happens behind the adaptor, so its effect is *not*
    > magnified by the adaptor. But the effect of shake is magnified by a
    > tele adaptor (and reduced by a wideangle one) because, to the camera,
    > it
    > looks like the world is shaking and the adaptor magnifies the apparent
    > movement of the world.
    >
    > Dave


    Thanks, Dave. IIRC, you said earlier that /if/ the adapter was fixed,
    then the stabilisation would work correctly. It's the effect of shaking
    the adapter which requires a change in the stabilisation? Just to
    clarify.

    Thanks,
    David
     
    David J Taylor, May 20, 2008
    #12
  13. Dave Martindale wrote:
    []
    > In theory, you could also cause blur by roll around the camera optical
    > axis, but (a) the amount of blur is not magnified by the lens focal
    > length, and (b) there's no simple way to compensate for this anyway.
    > So stabilized lenses do not correct for roll motion, to the best of my
    > knowledge.


    That's the one place where in-body IS wins over in-lens. In-body
    roll-correction would supplement the in-lens pitch and yaw quite nicely.
    Some people do poke at the shutter release, causing a roll of the camera
    just at taking time.

    Some Pentax cameras have in-body rotation correction, I believe.

    Cheers,
    David
     
    David J Taylor, May 20, 2008
    #13
  14. Woody Wordpecker <> wrote:
    > On 19 May 2008 22:31:46 GMT, Chris Malcolm
    > <> said:


    >> Chris Malcolm DoD #205


    > Interesting word there, "infirmatics". Is that a discipline
    > dealing with treatment of infirm people?


    > But the next line says "informatics".


    >> IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK


    > Was "infirmatics" originally a typo in the e-mail address, a
    > typo that may yet live long? Or is there a deeper meaning
    > that we can't comprehend without further enlightenment?


    I though it was a bit of obvious address munging which would defeat
    spamming robot address harvesters but be obvious to a human being.

    --
    Chris Malcolm DoD #205
    IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
    [http://www.dai.ed.ac.uk/homes/cam/]
     
    Chris Malcolm, May 20, 2008
    #14
  15. Dave Martindale <> wrote:
    > Chris Malcolm <> writes:


    >>Unless the IS system was adaptive, noting its over- and underestimates
    >>and adapting to cancel them out. I don't know if any camera maker uses
    >>such a system, but it's well understood how to do that well, and it
    >>automatically avoids the problems of being improperly informed.


    > To do this, you'd need images fed back from the sensor to the
    > stabilization system, plus some moderately powerful hardware to do the
    > correlations. Doing this in a video camera would be relatively simple,
    > since it's already producing 60 images per second. A P&S camera could
    > do the same, likely at a somewhat slower frame rate.


    You'd only need that kind of high speed adaptation if people were
    capable of changing their camera lenses frequently at sub-second
    speeds. In practice adaptation which took a whole second would be more
    than acceptable, which is a low enough loop to be no problem.

    > But a *film* camera cannot provide any image feedback at all, and most
    > DSLRs provide only one image.


    You don't need to keep historic images, only the errors in the
    feedback parameters, at most a few numbers.

    > A stabilization system for use on these
    > cameras has to operate open-loop, without feedback, so that's what all
    > the Canon and Nikon stabilized lenses must use. P&S cameras, and DSLRs
    > with live LCD preview, *could* have IS with image feedback for
    > self-tuning, but so far I haven't heard of one using it.


    It's quite possible to use open loops for high speed the parameters of
    which are checked and adapted over longer timescales in order to adapt
    to changing operating condititions. This is commonplace textbook stuff
    in control theory. Maybe no digital cameras currently use it, but all
    they'd need in order to use it would be an appropriately educated
    graduate.

    --
    Chris Malcolm DoD #205
    IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
    [http://www.dai.ed.ac.uk/homes/cam/]
     
    Chris Malcolm, May 20, 2008
    #15
  16. Chris Malcolm <> writes:

    >You'd only need that kind of high speed adaptation if people were
    >capable of changing their camera lenses frequently at sub-second
    >speeds. In practice adaptation which took a whole second would be more
    >than acceptable, which is a low enough loop to be no problem.


    Ok, so you're talking about continuing to run the stabilization
    open-loop, but having a slower closed loop to adjust the open-loop
    parameters.

    But you still need some sort of image feedback, to determine how
    much image motion remains given a measured amount of shake and a
    known amount of compensation for that shake. In other words, you need
    an error measure.

    >> But a *film* camera cannot provide any image feedback at all, and most
    >> DSLRs provide only one image.


    >You don't need to keep historic images, only the errors in the
    >feedback parameters, at most a few numbers.


    Right, if the stabilization continues to run open-loop when it's being
    used (not calibrated).

    But you still need image feedback for calibration. A film camera just
    doesn't provide that, so stabilized lenses designed for use on a film
    camera can't use this to adjust themselves. With a DSLR, you could
    provide a tuning mode, where you handhold the camera and intentionally
    provide a small amount of shake, while the camera fires the shutter
    repeatedly and adjusts the stabilization parameters. This should be
    eminently workable when the stabilization and image processing are in
    the camera body, and somewhat more difficult if the stabilization
    hardware is in the lens.

    >> A stabilization system for use on these
    >> cameras has to operate open-loop, without feedback, so that's what all
    >> the Canon and Nikon stabilized lenses must use. P&S cameras, and DSLRs
    >> with live LCD preview, *could* have IS with image feedback for
    >> self-tuning, but so far I haven't heard of one using it.


    >It's quite possible to use open loops for high speed the parameters of
    >which are checked and adapted over longer timescales in order to adapt
    >to changing operating condititions. This is commonplace textbook stuff
    >in control theory. Maybe no digital cameras currently use it, but all
    >they'd need in order to use it would be an appropriately educated
    >graduate.


    And, if the stabilization hardware is in the lens instead of the camera
    body, a redesign of the firmware in the lens so it can provide angle
    measurements and compensation data to the camera body, plus accept
    corrections to its stabilization parameters and store them in flash
    RAM.

    Most stabilized lenses for SLRs were probably designed in a time when
    their most common use was on film cameras, without external adjustment
    in mind. I agree it would make sense to add this in new designs.

    Dave
     
    Dave Martindale, May 20, 2008
    #16
  17. "David J Taylor" <-this-bit.nor-this-bit.co.uk> writes:

    >Thanks, Dave. IIRC, you said earlier that /if/ the adapter was fixed,
    >then the stabilisation would work correctly. It's the effect of shaking
    >the adapter which requires a change in the stabilisation? Just to
    >clarify.


    That's how I see it. The usual add-on adapter acts as a telescope,
    with a virtual output image projected at infinity. If the adapter is
    fixed, it will add no shake of its own and the virtual image will be
    stationary in the real world. A camera shooting through the fixed
    adapter would see shake, but the shake would only be produced by motion
    of the camera's own main lens, which its own stabilization system would
    be able to correct.

    (I'm ignoring for the moment any vignetting or distortion that would be
    cause by the optical axis of the camera lens not aligning with the
    optical axis of the adapter - these would likely prevent this method
    from being useful in practice).

    But when you mount the converter on the camera, and both move together,
    you change the amount of image shift you get for a given amount of
    camera shake, and the stabilization system needs to change the amount of
    correction it applies - so it needs to know the magnification of the
    adapter. I wouldn't describe it as "shaking the adapter" so much as the
    adapter modifying the effective focal length of the camera lens.

    However, if you did shake the adapter and camera *independently*, you'd
    need to measure the shake of both of them, as well as knowing the
    magnification of the adapter, in order to compensate.

    Also, note that all the above applies only to afocal adapters installed
    in front of the camera main lens, regardless of how the camera does its
    stabilization (lens element or sensor movement). Other optical
    configurations would have different properties. For example, if you
    use a teleconverter between the lens and a SLR camera, and the lens has
    internal stabilization, it doesn't need to know about the teleconverter.
    The TC magnifies the effect of the shake *and* the stabilization by the
    same amount, so no compensation is needed (but any remaining error will
    be doubled). But if the stabilization is done by moving the sensor, the
    teleconverter magnifies the effect of the shake and not the
    compensation, and the camera needs to know about the TC magnification
    factor to adjust the compensation correspondingly.

    Dave
     
    Dave Martindale, May 20, 2008
    #17
  18. Dave Martindale wrote:
    []
    > Also, note that all the above applies only to afocal adapters
    > installed
    > in front of the camera main lens, regardless of how the camera does
    > its
    > stabilization (lens element or sensor movement).

    []
    >
    > Dave


    Thanks, Dave. All understood and agreed.

    David
     
    David J Taylor, May 20, 2008
    #18
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