Sunday, February 5, 2012

Canon Didn't Want Me to Take This Photo

The talented Tona "Moonkitty" Willet  (

One of the joys of learning the technical capabilities of your equipment is running up against manufacturer-imposed restrictions that make no sense.

In the case of Canon, it's the ridiculous inability to use rear-curtain (2nd curtain) sync and their wireless E-TTL system together. Nikon can do this, so there's no technical reason why Canon can't do it as well.

Quick technical note: most digital SLRs still use mechanical shutters, with two curtains. The first one opens at the start of the exposure, revealing the sensor, and the second one moves later to end the exposure. Rear curtain sync is when the flash starts firing as the second shutter curtain begins to move, and is almost always preferable to front-curtain sync.

This matters because the photos in this post simply don't work without being able to rear-curtain sync multiple off-camera strobes. The light patterns and movement trails just don't come out quite right if the flash comes and freeze the motion at the beginning of the exposure. For starters, the LED light trails from the hoop won't superimpose over the dancer's body so cleanly. Second, her motion trail, if she leaves one, will look all wrong.

So, working within Canon's E-TTL Wireless system, you can't shoot these photos right. And, Canon won't rear-curtain sync with just any old standard radio trigger. So, how did I make it work, despite Canon's best efforts, and without expensive, Pocket Wizard-class, radio triggers?

Optical slaves.

 I have a pair of LumoPro LP 160s, that feature built-in optical slaves (another Canon omission that has no technical justification). I used a Canon 430EX II on my Canon 60D, set to minimum power and rear-curtain sync, to trigger the LP 160s via their optical slaves. The LP 160s were set to the left and right of the stage to cross light the performer, zoomed to the 105mm setting, but bare of any modifiers.

This, plus a tripod and a 2-2.5 second exposure, gave me lovely light trails from the hoop, and a solid, sharp dancer in the center.

There is, of course a downside to using dumb optical slaves in any situation where there are other folks with cameras around, as there were here. To wit: every time their flashes go off, so do yours. This can be a great way to completely burn out a flash, or have your flashes go off at the wrong time, or have your flash be in recharge mode when they should be going off, causing you to miss a shot. Keep that in mind if your decide to try this for yourself.


  1. I absolutely love your blog and your work Paul.
    You have an artistic way at looking through your lens. Thanks for sharing the technicalities. Check out my blog with art and poetry
    I would love to know what you think about my art.
    I will try to find you on google+
    xx Maryla

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