Tuesday, June 9, 2009

Canon and Rear Curtain Sync

GT Kung Fu Kicks
A few nights ago, I was taking shots of a friend, using a slow shutter speed to try and capture some nice night lighting. But (of course!) we had a sword, and hoodies galore, so fast action martial arts was the call of the day. What to do?

Use flash to 'freeze' the action. No biggy. But what about the ambient exposure blur during the frame? Well, everyone knows, you just use 2nd (rear) curtain sync, so the movement happens during the early part of the exposure, and then the flash goes at the end, giving a nice sharp final image. Easy!

The problem is, Canon (in their wisdom?!) decided that the only way you can do 2nd curtain sync is if you have a flash on the camera, and NO other flashes.

I'll let that sink(sync?) in for a moment. WTF? Seriously.

Rear Curtain Sync Solution
As soon as you add a second flash, and have the on-camera flash acting as master, you just lost 2nd curtain sync capability. WTF?

As soon as you put an unrecognized flash, or a remote trigger on the camera, you lose 2nd curtain sync.

Obviously unacceptable to any strobists.

The solution? Use an optical trigger. Thanks goes to Rαfα on flickr.

Now I've tested this, and a few things I've worked out:

  • It works with Cactus V4 triggers.

  • If you go faster than 1/25th, the 40D (and I'm going to assume others) switch back to 1st curtain sync anyway.

  • If you plug a PC sync cable into the side (with a flash on top) you get 1st curtain on the PC sync port, and 2nd curtain on the flash.

  • It works with an OC-E3 cable. Get a long one and half your problems are solved.

  • Nikon SB-26 slave mode also works a treat!

In this final picture, I used a 5 second exposure (to get nice burn in of the ambient tungsten lights), and had a 580EXII on OC-E3 (left) triggering via the Cactus the 580EXII at rear, and the Nikon SB-26 (right) triggering via its optical slave mode. All fired on the second curtain, at the end of the 5 seconds.

Rear Curtain SyncProblem solved.


  1. Hmm

    I have tried to replicate with pocket wizards but no joy so far.


  2. Hello,
    Was your camera also firing 2 flashes on each photo at that time (pre-flash and real/fill flash)?

    I have Canon 40D and Civica, small ext flash with built-in optical slave.
    I can only trigger Civica by Canon 40D int flash on rear-curtain flash mode max at 0.8s. At 1/3 stop longer (1s), Civica won't trigger at all.
    As you know, Canon 40D int flash on rear-curtain flash mode fire 2 flashes (pre-flash and real/fill flash) at each shot whatever E-TTL II mode is (Evaluative or Average). I also tried to disable the pre-flash but no avail thus far.
    My Civica's optical slave is rather smart device. It will ignore pre-flash from Canon 40D internal flash, and only trigger when real/fill flash from Canon 40D internal flash fire. Thus max time between pre-flash and real/fill flash that triggering Civica is 0.8s, slower than that Civica won't trigger at all.
    Then regarding my incapable abobe I was wondering how can you possibly using 5s exposure time!
    Is there really exist optical slave trigger that ignore pre-flash & recognize real/fill flash in 5s exposure long? Or is there other trick behind this?
    I hope you can give me some enlightenment here ^_^
    Best regard

  3. Denni, I didn't use ETTL, so no pre-flash at all. The Optical slave I was using is very simple - it doesn't detect pre-flash :)