Rear Sync not working or I'm not working?

Discussion in 'Canon EOS' started by zvia_shever, Feb 18, 2008.

  1. I have been trying different techniques with flash to get away from the "deer in the headlights" look in
    indoor low light situations. I've practiced and had success with flash exposure compensation, dragging
    the shutter and bouncing off walls and far so good. But, I've been trying, and failing, to
    duplicate a tip I found in a book regarding rear sync and using it to balance flash and ambient light.

    I always thought rear sync was only used in "moving" affects like trailing headlights etc... But, according to
    this book, rear sync can open up your background in a dimly lit room and in addition make your subject
    less flashy looking. Simply set your flash to rear-sync and voila, the shutter stays open longer, the flash
    fires at the end and you've got a more balanced, less flashy picture. The problem is, this isn't working for
    me at all. I have tried setting the rear sync/2nd curtain on the flash, on the camera (custom function 15
    on 30D), on both etc...but I'm seeing no difference. I'm using P mode so the camera is setting the the
    shutter speed at 60 and the aperture at 2.8. My high speed sync is off. Am I using the wrong mode? Do I
    have to be in AV mode for this to work? If so, I absolutely can't hand hold as the AV mode is set to slow-
    sync in low light. Is it me? Is it the flash? Is it the camera?

    Also, looking for any advice on using flash in low light outdoors....again, trying to get rid of the deer in
    the headlights look. I know I could drag the shutter or use AV/slow sync and a tripod, but looking for tips
    on hand holding in low light with a flash.

    Finally (promise), does anyone use the Lumiquest softbox outdoors? I tried the StoFen Omnibounce but
    it's no use outdoors where there's nothing to bounce off. Wondering if the Lumiquest softbox is any better
    or just a waste. I'm just looking for something to soften the light when I use a flash as fill in bright
    daylight and to diffuse the flash in low light situations where I cannot bounce.

    Sorry for the long post and multiple questions....Zvia
  2. Did the book say rear sync? Not slow sync? Most of the time for rear sync to be effective the shutter has to drag a bit to allow for the ambient light motion blur. It doesn't guarantee a slow enough shutter to expose for the available light. Especially in P mode. Kelby uses Nikons and if you turn the camera to rear sync it automatically goes to rear/slow. Funny thing is with a canon all you have to do is put the camera in Av mode and it will automatically expose for the ambient light even with a flash on (perfect for your given situation but usually a bad thing for most occasions). No settings are necessary. (just make sure you haven't set the cust func for the 200th sec min shutter speed in Av mode).

    This is actually one of the problems I have with Canon is no ability to set a floor shutter speed aside from 200th of a sec in Av mode. If you are hand holding in Av mode in low light the shutter may drag for seconds ruining any chances for a usable shot and locking your camera up for ? seconds. Your only option to expose the background is to to it yourself manually. If you expose the background manually you can set a hand holdable shutter to expose as much of the background as possible while the flash does the rest of the work.

    You can use the sto phen without bouncing it off of anything. Just point the flash head up and shoot, but you have to be close. The
    lumiquest boxes aren't really good in my opinion. They looked pretty harsh for a soft box.
  3. I'm absolutely not an expert when it comes to your flash - I'm much more of an outdoors natural light kind fo guy. That said, every Canon EOS system I've owned or laid my hands on (a couple of film rebels, ELAN & ELAN II, Rebel XTI, 20D, 5D) essentially defaults to the "flash setting" of aperture and shutter speed when in the P mode. If you want your aperture and shutter speed to capture the abient light, and then fill with the flash, you must use the Tv or Av or M modes.

    I've heard some say that the P mode is essentially the same as the green idiot box mode - I'm not sure I'd go that far. It's a pretty handy way to get a middle of the road exposure and quickly tweak to what you need. However, with regard to flash photography, I believe the P mode is essentaily the same as the green box mode.

    Try one of the other shooting modes and see what you get.
  4. I've never heard of rear sync, perhaps the book meant 2nd curtain sync.
    Manual exposure is the best way to make this work, where you set both the aperture and the shutter speed to match the ambient light, that way you know your shutter will be at a duration that you can hand hold.
    Shutter priority may also work for you, but I would really recommend manual.
  5. Your problem is the "P" mode - it overrides any settings you dial in because the camera auctomatically switches to the synch speed and determines the aperture. You should work in M mode, or at least in Av. If you've all along used P then therein lies your problem. Use Av and the camera will expose for the ambient lighting plus use flash to expose your main subject.
  6. Thanks for all the responses.

    The book said rear sync, not slow sync....but it was Kelby, so Tak, your explanation about
    the Nikons going into rear/slow in rear sync makes complete sense. I had a feeling he
    meant slow sync, especially as he mentioned to keep the camera still as the shutter speed
    would slow down.

    As far as P mode vs. Av vs. M, I agree with you Denny, that P mode is sort of like the green
    idiot box mode (which, I promise I never touch :). I use AV mode 90% of the time and
    have been playing around with M and trying to get used to it. But in low light, it's simply
    hard to get a fast enough shutter speed to handhold without raising the ISO so much that
    I get really noisy pictures. So far, the only thing that comes close to working for me is
    what Kelby calls 'dragging the shutter'. I put the camera in P mode (with flash on) and
    plug in those numbers into manual but instead of using the P mode's recommended
    shutter, I lower it from 1/60 to 1/15. I've tried it and it does let in more ambient light, but
    again, 1/15 is not easy to hand hold, but at least easier than slow-sync in AV mode.

    Any more advice on M mode in low light would be greatly appreciated. Thanks again, Zvia
  7. I shot nearly all of my wedding formals and candids with rear synch, which I've also understood to be called 2d curtain synch - first curtain is when (front) curtain opens and second curtain is when (rear) shutter closes.

    I've never read the book you mentioned, but I learned years ago that images do indeed look much less "flashed" using this technique.

    I always shoot in Manual for weddings (Canon 1D3's and 1Ds3's) with Quantum (formals, groups and dancing, etc) and speedlights for candids, etc. The rear curtain synch will not work with wireless operation of the speedlights, wireless operation must be turned off for the rear synch to function properly (or at all with new 580EX2).
  8. Chris, I'll do some experimenting in manual mode with a higher ISO and 2nd curtain/rear
    sync and see what I get.
  9. Zvia,
    I am not an expert, but someone like you who is learning the flash. I worked with the 2nd curtain sync and had the same problems. What I learned (hopefully someone will chime in to say if I am right or wrong) is that the shutter speed of 1/60 or even 1/15 will be to fast for your eyes to see the difference in the flash speed. It's probably working, just your eyes are seeing it go off just after you press the button. I think the shutter is going down and back up to quick for you to see a difference at that speed. I had to drop my shutter speeds below a second to see a difference. You'll need a tripod. The second thing on the Canon flashes make sure you have the 2nd curtain sync setting on. Its the high speed flash/2nd curtain sync (>>>, my attempt to use the key board to copy the manual). Give it a try, drop the shutter speed down some more and put it on a tripod, this way you can see it working.
  10. Aaron, thanks for the suggestion. While in Program Mode, I set the the 2nd curtain in the
    camera and on the flash (>>>)....tried all kinds of combinations. I think the answer comes
    down to exactly what you said, ie: at 1/60 or even 1/15, unless one has bionic eyes, it's
    too quick to tell when the flash goes off. As others pointed out, Program mode is a
    problem as the shutter speed is set to 1/60 when using flash...definitely too fast to see the
    effects of rear-sync/2nd curtain.

    I am going to try your suggestion with the tripod and also set it in Manual mode per the
    advice of the others.

    Thanks everyone! Zvia
  11. I've read several discussion of 2nd curtain (aka rear-sync) flash, and am still confused. I understand how the choice of 1st- (normal) or 2nd-curtain flash affects motion, but I don't understand how it affects--if at all--background exposure, unless exposure itself is affected by the choice of when the flash fires.
    I want to know what the camera is thinking when 2nd-curtain has been selected (with flash set on, and, let's say, AP selected). Is it thinking, "since 2nd-curtain is the setting, I'll assume the photographer wants to expose the picture properly with ambient light before I fire the flash, so, as well as delaying the flash, I'll set the shutter speed based on ambient light alone"? If it doesn't think this way--i.e., if it bases the exposure on the flash--and if there is no motion, the choice of 1st- or 2nd-curtain flash would have no bearing on the shot, yet I've seen side-by-side comparisons where the background (in a night shot, for example) is much brighter with 2nd-curtain than with 1st-curtain. If the camera does choose exposure based on ambient light alone when using 2nd-curtain, might I sometimes want to expose for the background, lock the exposure, then recompose on the foreground subject (and possibly dial-down exposure compensation)?
    Zvia mentioned another approach: "I put the camera in P mode (with flash on) and plug in those numbers into manual but instead of using the P mode's recommended shutter, I lower it from 1/60 to 1/15." (Zvia, I assume you meant "with flash off", and you'd then turn the flash back on after getting the exposure. Correct?) In the previous paragrah I'm asking if 2nd-curtain works pretty much like this, except for when the flash goes off, and recognizing the shutter speed/aperture combination may be different, but would give the same exposure.
    Does any of this depend on camera make, e.g., Nikon vs. Canon?
  12. Boy, was I ever off-base (see previous message above). As a relative newbie, I should have known to do more research ("Part II" of the so-called Canon flash bible, at, was especially useful), and to make some tests with my camera (a Canon G10). What I found was that background exposure with a flash depends mainly the shooting mode (P, Av, Tv, M), and appears to be independent of whether 1st or 2nd-curtain has been selected (Tv being shutter-priority.)
    For Canon DSLR's, I've read that, in P mode, the camera assumes it is being hand-held, and accordingly chooses a shutter speed no slower than 1/60 second (and up to the sync-speed, e.g., 1/250 sec.), resulting in a dark background in low-light conditions. In Av mode, it exposes the background correctly, even if this means a very slow shutter speed. It works similarly in Tv mode, except, of course, there might be insufficient light to expose the background at the widest aperture. It appears that, to expose the background correctly, the camera looks at the outer metering zones (since it is using the flash to light the subject). Just how it (and other mfgs.) do this seems to be proprietary information.
    I expected my Canon G10 to work the same way, but found it operates a little differently. In Tv and M modes it works the same, but to properly expose the background in Av mode, I must turn on "Slow synchro" (and slow sync can also be used with P mode). In effect, slow synchro is always on in M and Av modes.

Share This Page