Is X-Sync speed a "big deal" anymore - now that we have High-speed synch on powerful flash units?

Discussion in 'Digital SLR' started by C J Southern, Dec 24, 2005.

  1. C J Southern

    Jeremy Nixon Guest

    That doesn't make sense. For flash exposure the shutter speed is
    unimportant; exposure will be the same at 1/125 as at 1/250 or 1/60, with
    the same aperture, unless ambient light is also contributing. Getting
    f/2.8 with strobes has nothing whatever to do with the shutter speed.
    Jeremy Nixon, Dec 26, 2005
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  2. C J Southern

    JPS Guest

    In message <v55rf.10307$>,
    There is another limitation, which can be quite serious when trying to
    stop action. If you are set to 1/320, etc, the duration of the flash
    can be many times as long as it is with normal sync, so 1/320 can give
    much more motion blur *and* possibly staggered into vertical strips)
    than with normal sync (which can be as fast as something like 1/10000).
    After all, HP sync is merely a strobe that lights the scene for as long
    as the shutter is open; not a single pulse of light that illuminates the
    frame all at once.
    I don't know about the 580EX, but the 550EX works just that way. It
    only uses high-speed sync if it is enabled on the flash, *and* the
    camera is set to a fast shutter speed. If the flash is on, but
    high-speed sync is not, then the camera won't honor your chosen shutter
    speed, and give you the normal sync speed instead. If high-speed is on,
    and the shutter speed is less than the sync speed, then normal sync is
    always used.
    JPS, Dec 26, 2005
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  3. C J Southern

    JPS Guest

    In message <rA6rf.10321$>,
    1/320 is about 30x as long as the shortest normal sync flash possible,
    and will not stop a swung baseball bat, or the wing of a bird in motion
    (or even its head).

    In addition, the frame is exposed in vertical strips over a period
    slightly longer than the stated exposure time with high-speed (as is
    also true of ambient light exposures faster than the sync speed, as
    JPS, Dec 26, 2005
  4. C J Southern

    JPS Guest

    In message <1x6rf.10320$>,
    With the 20D and 550EX, normal-sync GN (at 105mm) is 55 (meters), and
    drops to 24.3 at 1/320. GN at 1/8000 is 4.9.
    JPS, Dec 26, 2005
  5. C J Southern

    Skip M Guest

    One thing I forgot about was ISO 50 on the 5D, that would get me an extra
    stop on the aperture. I'll have to try that.
    Part of my problem, besides the limited control, is the size of my "studio."
    It's my 11'x14' family room. Not enough room for a lot of devices.
    That, and I'm learning on the run...
    Skip M, Dec 27, 2005
  6. C J Southern

    Skip M Guest

    Like I said earlier, I'm still learning this part, not real experienced with
    studio strobes. I'll try that, next time.
    Skip M, Dec 27, 2005
  7. C J Southern

    Skip M Guest

    Thanks, like I said, I'm still learning on the run with some of this
    Skip M, Dec 27, 2005
  8. C J Southern

    Jeremy Nixon Guest

    With strobes, the exposure time is irrelevant because the exposure time is
    determined by the flash, which is (necessarily) of shorter duration than
    the actual shutter speed. You can set any speed up to the camera's maximum
    sync speed, and it doesn't matter in terms of exposure; the reading on the
    light meter for aperture is all that matters.

    The meter has a shutter speed indication because it also measures ambient
    light and determines the amount of contribution it makes to the overall
    exposure. Shutter speed does matter for any ambient light, of course.
    In a typical studio setup, the ambient light contribution will be zero.
    My meter indicates this by saying "100%" for the flash contribution.
    Decent studio strobes will shut off the modeling light when they flash,
    so even those won't affect the image. (What's interesting about that
    is that it's too fast to see; I "know" mine shuts off the modeling light
    because it says it does, but I never actually noticed it. I'd imagine
    that you could use a slow enough shutter speed to catch the modeling
    lights on; obviously the power pack has no idea what your shutter speed
    is set for.)

    Older flash meters like the ones I learned with don't have any shutter
    speed setting or indication because they measured only the flash.
    Jeremy Nixon, Dec 27, 2005
  9. C J Southern

    Skip M Guest

    Ok, I get that, now. I took a lighting class a few years ago, but didn't
    use strobes then, and that part of the class didn't penetrate, apparently.
    But it's coming back to me, as I read what you wrote.
    That makes sense, now. My meter does that, too. I'm guessing that my
    strobes do, too, but I've no confirmation of that. OTOH, the modeling light
    is so weak that I'm not sure what difference it would make. It's about 100
    I just started using strobes late last year, it's not something I'm familiar
    with, obviously. When I started working with studio stuff, strobes were out
    of my budget, so I stuck to floods. The price has come down, and my budget
    has gone up to meet it, but I appreciate the help. I have a shoot coming up
    that I'll put this to use for.
    Skip M, Dec 27, 2005
  10. C J Southern

    C J Southern Guest

    It works fine with the ST-E2 Transmitter and 580EX Flashes. It's a setting
    on the transmitter - you don't even have to adjust the 580s.
    C J Southern, Dec 27, 2005
  11. C J Southern

    C J Southern Guest

    I was thinking that the strobing wouldn't necessarily have to continue for
    the full duration of the shutter opening, but thinking about it I can now
    see that it would have to (another penny dropped!). Am I correct in assuming
    that the X-Sync speed is really nothing to do with timing per sec - it's
    simply the fastest speed that both shutter curtains are fully open for the
    complete duration of the exposure?

    I know that the flash is cycled at around 50,000 times per second, but can
    anyone tell me if the "brightness" is adjusted by changing the flash
    intensity, or by changing the on-time -v- off-time in each 1/50,000 cycle?


    C J Southern, Dec 27, 2005
  12. C J Southern

    C J Southern Guest

    I think another penny just dropped ...

    I've been thinking that ND filters are a thing of the past, but now that I
    think about it, if you're in a situation (say an outdoor wedding on a bright
    day with a very 'reflective' bride in white) where you want to use fill
    flash - you don't want to use HSS mode - and you don't want a large DOF then
    ND filters are the only way you're gunna get your speed below X-Sync?


    C J Southern, Dec 27, 2005
  13. C J Southern

    Skip M Guest

    That same penny dropped, here. Excellent suggestion, and an easy solution.
    Skip M, Dec 27, 2005
  14. C J Southern

    Alan Browne Guest

    The white dress should not expose improperly at EV 15 (sunny 16) in the
    sun. The usual problem with the white dress is the metering of it, not
    the recording of it. Incident metering is best in this case, or at
    least meter the brightest white and then open up 2 to 3 stops (color
    negative film. If you're shooting 160 at 100, then 2 stops should suffice).

    But indeed, if you want fill flash and/or a large aperture, and esp. if
    the 400 (from the church ceremony) is still loaded, then one recourse is
    the ND filter. I carry 2 and 3 stop 72mm filters in my bag giving me
    the flexibility to adjust. It doesn't happen all that often, but it
    does happen. In the studio too, esp. with my limited strobes (1/1, 1/2)
    it's neccesary to have them.

    Alan Browne, Dec 27, 2005
  15. C J Southern

    Alan Browne Guest

    That's a great advantage. A year or so ago I was at one of the stores I
    frequent and a Nikon oriented pro was looking at the Canon 20D (IIRC)
    because he needed the ISO 100. He had a D70 but the ISO 200 was causing
    Hmm, my studio, 14x14x14 is being converted into a "living room" at the
    insistance of my SO ...

    Additional point: damping the light of an Auto or TTL flash (with say a
    white cloth) does not work (unless it is in manual mode) as the system
    will pump out more light to overcome the dampening. With manual strobes
    or studio strobes, it works perfectly, of course.

    Alan Browne, Dec 27, 2005
  16. C J Southern

    Alan Browne Guest

    Not quite. Most recent meters calculate the flash to ambient ratio. So
    if the shutter speed is slow enough you will get overall exposure as
    well as an indication of the contribution from ambient in the shot.
    You're missing the point of the % indication when used with flash. It
    is sometimes desirable to include ambient light with flash light, and
    the % indication allows you to figure the conribution from each source.

    As to shutting off the modeling lights, that's irrelevant for most
    studio shooting, typically at 1/500 (or at least 1/250 for a high end
    SLR) as the ambient contribution from a few watts of tungsten (eg:
    1/500s X 200 W = 0.4W-s) v. the 100's W-s of flash power will not record
    on the film at all. For 1/60 shots, it may be a bit more useful, but
    again, the contribution v. the strobes is probably far too little to record.

    Alan Browne, Dec 27, 2005
  17. C J Southern

    Alan Browne Guest

    Yep. For bonus points, a front sync will fire when the first curtain is
    fully open and a rear sync will fire immediately before the rear curtain
    begins closing. This is important to record movement trails (ambient
    light) on moving subjects before "freezing" the subject.
    In HSS, it does cycle. In normal mode it is DC. The actual rate is
    manufacturer / model dependant.

    The duty cycle (% of time on and off of the 50,000 Hz pulses) determines
    overall brighness for HSS. The duty cycle may change with HSS shutter
    speed, I don't really know but that would be a good assumption.

    For normal thyristor shutoff flash (normal TTL), it discharges at full
    power and current and then keeps discharing at lower and lower power
    until the thyristor cuts it off or until drained.

    Alan Browne, Dec 27, 2005
  18. Flash intensity is set by the on-time anyway, so both possibilities
    are the same.

    Wolfgang Weisselberg, Dec 27, 2005
  19. C J Southern

    Patrick L Guest

    That is precisely what I was stating.

    Patrick L, Dec 29, 2005
  20. C J Southern

    Matt Clara Guest

    It sure does on my large-format, medium-format, and 35mm gear. Also, with
    the D70, it's possible to create some really weird artifacts pushing the
    sync to its limit (1/8000 of a second, baby).
    Matt Clara, Dec 29, 2005
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