Tuesday, August 31, 2010

Pushing Flash Sync Speed

Pushing the Sync Speed?
Those from the B&W film era will remember push processing film. In digital we used to push the ISO in the days when cameras topped out at ISO 800 or lower. Today I want to demonstrate pushing the camera's flash sync speed. The result is a bit different from pushing ISO, as it is not uniform across the frame (okay, it isn't a perfect analogy). However, the effect is quite distinctive and can be put to good use.

Out of Sync Flashing
To demonstrate pushing the flash sync speed, I've shot some blank frames at various shutter speeds.

Here is an exposure at 1/200, f/4, triggering the off camera flash with a cable system. Since 1/200 is within the camera's maximum sync speed, the exposure is fully illuminated by the flash.

For this exposure I bumped up the shutter speed up to 1/400. Notice the black bar at the bottom. This results because the shutter is never fully opened above the maximum sync speed and the flash fires very fast, in this case somewhere around 1/10000 because it was at minimum power. In order to fully illuminate the frame, the flash would need to fire multiple times, which is what High Speed Sync (HSS) is all about. For more information on shutter/flash synchronization, take a look at this excellent post at the Digital Photography School.

This exposure was at 1/800. Note how even less of the frame is exposed.

As an aside to this little experiment, I was curious how much a wireless trigger would affect the flash synchronization, so this shot was made using the Yongnuo CTR-301P, again at f/4 and 1/800. As you can see, the flash doesn't happen until after the shutter is completely closed.

Again with the Yongnuo CTR-301P and at f/4, but this time at 1/400. The timing appears to be very similar to using wired triggering at 1/800.

Ever full of curiosity, I tried my other wireless trigger set, the Yongnuo RF-602 to see if this newer, improved model has an edge over the older triggers used for the previous exposures. At 1/800 you see just a sliver of light along the edge, which tells us that it is a little bit faster.

The RF-602 at 1/400 shows just a little more exposed area than with the CTR-301P at the same shutter speed, again confirming slightly faster triggering.

Mixing it Up, Flash & Ambient
Before putting pushed flash sync to practical use, let's take a look at what happens when ambient light is brought into the exposure. In this case the ambient light is my ceiling lights, which are bright enough to factor in with the exposure.

My ceiling lights at f/4 using flash (aimed poorly) and a shutter of 1/800. We get the familiar dark area, but you will notice that the lights show up in the frame even where the flash doesn't. This is of course because they are a continuous light source, so synchronization is not an issue. Keep this in mind for the next section where this concept gets put to some practical use.

Naturally Lit with Flash (pushing the sync speed)
This picture was taken with an 85 mm lens at f/2 and 1/800 supplemented with flash. The flash, a Vivitar 285, was mounted on a swivel bracket and set to auto-meter at f/2 using a camera mounted sensor via an extension cable. The maximum sync speed for this camera is 1/200, and since 1/800 exceeds the camera's sync speed, the bottom of the frame does not receive light from the flash, but since the camera is rotated clockwise, the bottom is now at the left. You can see that the left half of the frame is darker, as it only receives ambient light whereas the right side gets ambient plus flash.

The resulting image appears as if she is standing in partial shade. I think it works well and is a cool effect. I do have a confession to make. I stumbled upon this by using Aperture priority, which put the shutter at 1/800 causing this effect. However, once I realized what was happening I was able to use it to advantage.

A Smidgeon of Spot Editing
To finish the image I've burned down her left side (camera right) a little so that the light now appears to be a sliver hitting her directly in the middle. I think it adds a bit of interest and focuses attention even more directly on her face without appearing to be a retouch effect. That is, to my eye it still looks natural. Edits were done in Bibble 5 thanks to its spot editing features. Pretty cool, isn't it! What do you think? Have you ever used your camera's sync speed in this way? What other scenarios could benefit from this tool? I would like to hear your stories and ideas, so feel free to comment.

Coming Next
That's it for this post and this series. Hopefully you found this useful, or at least kind of interesting. I haven't worked out what to do next, so it looks like you get a grab bag.

Until then...



  1. Hi Gene. That's a nice use of this technique.

    I've used the technique (though not as artistically) in order to create an 'invisible flash' shot. I held an SB-800 with one hand, triggered via optical sync with a manual flash on-camera. Shooting above the sync speed, the rear curtain covered the flash (making it appear as if it didn't fire) while the flash illuminated my face. http://www.flickr.com/photos/13451101@N05/4947578084/

    I haven't found a practical, non-gimmicky use for this technique but yours is a great implementation of it.

  2. Hi Mic,

    That might be gimmicky, but it is creative and fun. Who knows, some day it could come in handy. One of those tricks you pull out of the bag that really wow someone.

  3. In a similar vain I discovered something about my Fuji S9000 hybrid camera by accident. It (apparently) has a leaf shutter that will sync with flash all the way up to it's 1/4000 top speed! I have to be hard-wired for this, but the interesting part is that you can use it to control your flash exposure by shutter speed instead of F. This opens up interesting possibilities.

    This of course will vary with flash unit model, I'm referring right now to battery-powered units such as a Canon 430EX running full power. I would imagine things would be interesting with a studio flash. I start getting attenuation typically above 1/500-1/640. I'm not sure if it's linear (as in actual per-stops) as I haven't experimented enough with this.

    I haven't checked it with optical triggers, but my cheapie Cowboy Studio radio trigger typically craps out around 1/400-1/500 or so, which certainly gives you additional triggering options versus focal-plane shutters.

    So anyway if you have a decent digital camera with a leaf shutter you may want to experiment with this technique.


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