canon 20D flash sync at 1/320?

Discussion in 'Canon' started by peter, May 19, 2007.

  1. peter

    peter Guest

    When I attach a canon speedlite 550ex (high speed sync off) on a 20D, the
    shutter speed automatically reduced to 1/250s if I had it faster.

    Is there a way to override this?

    I found by experiment, I can flash sync at 1/320s (the experiment is done
    with a 3rd party flash that does not change the shutter speed). So I would
    like to use this speed with the canon speedlite, but it won't let me.

    Any ideas? I checked all the custom functions and none of them look like it
    would help.
    peter, May 19, 2007
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  2. High speed synch should be turned on.
    John McWilliams, May 19, 2007
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  3. peter

    Alan Browne Guest

    As I'm sure you know, flash sync speed is driven by shutter mechanics.
    Faster shutters allow faster sync speeds, the best for FP shutters being
    1/300 (Minolta, Nikon). Canon max sync speeds are 1/250. (Some Nikon
    dslr's like the D70 also have electronic shuttering in the way they use
    the sensor thereby achieving 1/500 flash sync).

    It's tough doing fast shutters. Nikon have reduced the max sync in the
    F6 to 1/250 from 1/300 (F5). OTOH, the added value is also questionable.

    With my Maxxum 9 (flash sync=1/300) I can get 1/350 shots using the
    flash sync terminal. With my Maxxum 7D (flash sync=1/160) I can get
    1/200. With a Maxxum flash it of course limits it to 1/300 and 1/160
    respectively (and 1/125 with anti-shake activated).

    With that and your experience it's reasonable to assume that the max
    shutter speed is conservative by 1/3 to 2/3 of a stop to allow for
    manufacturing variance, environment (temperature) and aging.

    Bret and John recommend high-speed sync but that reduces your available
    power considerably, esp. when you get to 1/1000 and faster. Most of the
    flash light is wasted on the shutter curtains... it remains a good way
    to get shallow DOF on bright scenes where you want some action freeze
    and fill in the foreground.

    But then so does a ND filter with normal sync flash... and paradoxically
    due to the great inefficiency of HSS, you'll actually save flash
    batteries with a 2 stop ND in place once you're at 1/1000 (or so) and

    Alan Browne, May 19, 2007
  4. peter

    Ray Fischer Guest

    It's hard to know why you would want to.
    That's because 1/250s is the flash sync speed for that camera, and it
    will adjust the sutter speed accordingly.

    And, as a practical matter, it rarely matters much anyway sicne the
    flash speed it so much faster than the shutter. If you want to reduce
    non-flash light then you can also reduce the aperture or use a neutral
    density filter. Or turn off the lights.
    Ray Fischer, May 19, 2007
  5. peter

    peter Guest

    I don't want to, that why I turn it off.
    High speed sync is less powerful than low speed sync. Cheating the sync
    speed is equivalent to boosting the flash's output power when used as a fill

    Don't know why canon won't allow it even in manual mode. Why is it called
    manual mode if the shutter speed is changed automatically for me??
    peter, May 19, 2007
  6. peter

    peter Guest

    Thanks, you're the only reply that understands my need (almost). I do plan
    to use a ND filter to reduce DOF.

    If I can cheat the sync speed, I could effectively reduce the sunlight's
    intensity and enable fill-in flash at greater shooting distance, or save
    flash power at the same distance (battery pack last longer), and less
    blinding flash into the subjects' eyes.

    This auto-limiting sync speed in *manual mode* reminds me of parents who
    tell their child they can do whatever they want, and then meddle in the
    child's business.
    peter, May 19, 2007
  7. $Don't know why canon won't allow it even in manual mode. Why is it called
    $manual mode if the shutter speed is changed automatically for me??

    Remember that the output of a flash is controlled not by adjusting
    its intensity but by adjusting its duration. The more power you want,
    the longer the flash is on. The camera's maximum X-sync speed has to
    be designed such that it will not cause problems with the longest
    possible flash burst, which will depend on the flash unit but is
    usually more than 1 ms and perhaps as much as 2 ms. With the flash
    taking that long, that means that in order to achieve a maximum X-sync
    speed of 1/250, the shutter curtains must be able to make their full
    motion in 2 ms (during the first 2 ms, the first curtain opens; for
    the next 2 ms, the shutter is fully open; during the next 2 ms, the
    second curtain closes). 2 ms isn't a lot of time to take a physical
    device, accelerate it from rest to full speed and have it
    traverse the opening.

    Chances are that if you fire a full-power flash burst with the
    shutter speed set to 1/320, the second curtain is going to start
    closing before the flash has completed firing. Now, since flash
    output rises rapidly and falls slowly, the part of the flash burst
    that you're blocking as the second curtain starts to close is quite
    dim and likely will be very hard to spot in the results - but it's
    nevertheless not syncing correctly.

    On the other hand, if you fire a partial-power burst, it will take
    quite a bit less time, perhaps much less than 1 ms, and in this case
    there *is* enough time for the flash to complete before the second
    curtain starts to close, even at a shutter speed above maximum X-sync.

    As for why the camera doesn't allow you to pick a higher sync speed
    at least some of the time, well, the camera doesn't know how long the
    flash burst will be. That's controlled by the flash. And the flash
    may not know, either; among other things, it depends on whether you let
    the capacitor charge fully before firing the flash. The camera and
    the flash don't even know at what strength to fire the flash until
    flash metering is done, which (unless you use flash exposure lock)
    doesn't happen until after the ambient exposure value has already
    been set.

    Anyway, the bottom line is that the camera's specs clearly indicate
    that 1/250 is the maximum X-sync speed. If you expected something
    else, you were mistaken. If you absolutely need to use a flash along
    with a shutter speed that's only a third of a stop above what the
    specs say, go ahead and use a non-dedicated flash (the camera doesn't
    know it's there and therefore will not impose the maximum X-sync
    limit) and hope for the best.[/QUOTE]
    Stephen M. Dunn, May 20, 2007
  8. peter

    John Sheehy Guest

    High speed sync has many problems. It has a much lower GN, even at just
    1/3 stop faster than the x-sync (and gets progressively worse with faster
    shutter speeds). It wastes power, with the majority of light at any given
    time falling on the shutter curtains instead of the sensor. It has no
    action-stopping power, beyond the shutter speed, as it is basically just an
    auxilliary pulsing lamp.

    John Sheehy, May 20, 2007
  9. peter

    ASAAR Guest

    You should know the answer to that quite well. A larger aperture
    produces a smaller DOF. Depending on conditions (lack of tripod,
    slow shutter speed required for shot, already using lowest ISO,
    excessively bright day) it may be difficult or impossible to
    increase the aperture unless an ND filter is available.

    Technically, and rather obviously, an ND filter by itself has no
    effect on the DOF. Cameras have many interrelated attributes (think
    ISO/noise), but in the process of trying to show your mastery of all
    things photographic by winning an easy debating point, you show that
    once again a clear response that actually helps people probably
    isn't the primary goal. The flash complicates matters, and if you
    think that it would somehow prevent an ND filter from helping the OP
    to get a shallower DOF, it would have been nice to explain why,
    rather than baiting the OP with your question. You have better
    things to do, and as I've said elsewhere, Floyd is currently on a
    roll. Why not help him out. He needs you, desperately. :)
    ASAAR, May 20, 2007
  10. peter

    ASAAR Guest

    And of course you saw my reply as an "attack", just as I predicted
    you would.

    And as usual, your knee-jerk reaction is not to open the dialog
    that you profess to prefer, but to turn an imaginary attack into a
    real one.
    ASAAR, May 20, 2007
  11. peter

    ASAAR Guest


    The various games played by so many people under the guise of
    simple humor, flame wars, making sport, inventing lies, and other
    forms of believed light-hearted fun will stop immediately wrt to

    I will no longer tolerate any aspersions cast at me, my family,
    my career at work or in the military, or . . . or . . . oops.

    Whew! Please excuse. I don't know what came over me. Maybe it's
    the resemblence. Very slight. Very slight. No indication yet that
    meds are called for. :)
    ASAAR, May 21, 2007
  12. peter

    ASAAR Guest

    Interestingly, he made similar accusations a couple of months ago
    several hours after I praised him for posting the kind of helpful
    reply I was trying to nudge him towards, and which I knew he was
    knew he was capable of making. He sees things differently of
    course, but what I see is that he has a really hard time accepting
    criticism, seeing most positive criticism as negative, going so far
    as to equate it with "attacks". Contrast that with a number of
    others, especially from the much more mature Wayne J. Cosshall, who
    finds ways to recognize useful suggestions even from those that go
    out of their way to reply with insulting comments.
    ASAAR, May 21, 2007
  13. peter

    ASAAR Guest

    On 21 May 2007 15:23:00 -0700, acl wrote:

    OP :)::)
    ::: If I can cheat the sync speed, I could effectively reduce the sunlight's
    ::: intensity and enable fill-in flash at greater shooting distance, or save
    ::: flash power at the same distance (battery pack last longer), and less
    ::: blinding flash into the subjects' eyes.
    You didn't miss anything and the OP gave every indication that he
    fully understands the tradeoffs of using an ND filter. Proving my
    contention that if Roger had any useful, helpful, unobvious
    information to provide, he should have simply posted it, and it
    would have been to everyone's benefit. He later claimed that his
    reply was simply an "honest question", but his final, 'obvious'
    explanation shows otherwise, the condescending "How does an ND
    filter reduce depth of field?" was more likely asked for the reason
    I gave than Roger's face saving after-the-fact explanation.

    I showed how the ND filter could reduce DOF, said that Roger
    should also know the answer "quite well" and I'd be amazed if the OP
    hasn't also known that for many years, as well as most people that
    have purchased ND filters. As you've shown, owning and using an ND
    filter (or flash) is no great obstacle to understanding such a
    simple concept.
    ASAAR, May 21, 2007
  14. peter

    ASAAR Guest

    The problem is that you find it extremely difficult to admit the
    obvious. If a complete newbie asked "How does an ND filter reduce
    depth of field?" I'd have no problem believing that it was a simple,
    honest question. That you'd ask such a question and feign ignorance
    given your history of knowing and writing papers delving into the
    most minute, esoteric camera and photography details, such as
    (remember this?) trying to prove or demonstrate that DSLRs have as
    much DOF as point & shoot cameras, and then expect us to believe
    that you're asking someone to explain to you how a ND filter can
    reduce DOF? Give us a break! Whether we get along or rub each
    other the wrong way is of no matter in this instance. I readily
    admit that you know more about photographic minutia than most people
    here, and most ng regulars that have read your messages probably
    agree. But that doesn't mean that you can get away with pretending
    to not understand such a basic concept as to how an ND filter can be
    used to reduce the DOF. That's so simple one might almost expect it
    to be rejected from a "Dummies" manual. And all this to avoid
    having to admit the real motive for your question. Sheesh.
    ASAAR, May 22, 2007
  15. peter

    ASAAR Guest

    English translation: I remain no less resolute than SeƱor Bush
    when it comes to admitting no error or deception, despite
    overwhelming evidence sufficient to embarrass a Wolfowitz.
    ASAAR, May 22, 2007
  16. peter

    Alan Browne Guest

    I simply never came back to this NG since that posting, but the use of
    an ND to reduce DOF (by forcing a larger aperture) should be quite
    evident to most, whether or not flash is used. Yes, more flash power
    will be required, but it's still less than wasteful HSS.

    Alan Browne, May 22, 2007
  17. peter

    Rod Guest

    My 580EX has a high speed sync mode and I can pick
    any shutter speed I want. Don't know about your
    flash. I have found that using a slower shutter
    speed helps use more ambient light.
    Rod, May 23, 2007
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