Fig. 1–Shot during the Peter Read Miller Sports Photography Workshop in Denver. A pair of Speedlites working in high-speed sync provide essential fill flash for these fast-action cycling shots. Canon 5D Mk III, 17-40mm F/4L at 17mm, 1/500″, f/8, ISO 100. Two 600EX-RT Speedlites triggered by ST-E3-RT Transmitter.

High-speed action in broad daylight requires high-speed fill flash.  High-speed in this case means two things: the fast shutter speeds enabled by Speedlites in high-speed sync AND speeding up the flash recycling time by using an external power pack to recharge the Speedlites.

I’ve covered high-speed sync (HSS) many times on PixSylated. [For an introduction to HSS, check out this Simple Truths article.] The short version is that HSS changes the way the Speedlite fires. HSS enables the use of shutter speeds faster than the camera’s sync speed—1/250″ on most DSLRs.

The downside to HSS is that turning the Speedlite into a near-continuous light source (even for a fraction of a second) consumes a bunch of power. My tests have shown that HSS consumes 2.5 stops of light—which is the equivalent of turning a Speedlite’s maximum output from full-power down to 1/6 power. For fill flash, this power loss is not a big issue. It’s only when you are shooting day-for-night that you need to overcome the HSS hit by using an arsenal of Speedlites (like I did here).

To stop the motion of the cyclists speeding downhill, I had to shoot at 1/500″ or faster. The flash sync speed for my 5D Mk III is 1/200″. So, in order to have fill flash at this shutter speed, I had to activate HSS on my Speedlites–which requires one button push. Then, by stacking a couple of Speedlites, I was able to recover a bit of the HSS power loss (not all of it, but enough to extend the effective range of the fill light).

Other advantages of stacking Speedlites (whether using HSS or not) include:

  • each Speedlite fires at lower power, so they recycle faster
  • if one flash goes down during the shoot, you can keep shooting
  • there are no double shadows (which is an issue when shooting multi-flash brackets, check out the wall shadows in this example shot)

My Stacked Speedlite Rig


Fig. 2–A pair of Canon 600EX-RT Speedlites bound together with a Velcro strap. The external power cords on the sides are connected to the Bolt Cyclone DR PP-400DR Dual Port Battery Pack.

I’ve tried lots of ways to stack Speedlites over the years—gaffer’s tape, bungie cords, belts, etc. By far, the most reliable system (in terms of strength and ease) uses fat straps like these 1″ x 18″ Velcro straps on Amazon. One strap easily cinches the heads together in just a couple of seconds. The key is to use a strap that has a plastic loop sewn into one end. You gain a good bit of leverage by passing the strap through the loop and then pulling it back on itself to secure it. Just wrapping a strap around and around the heads is not enough. The strap has to pull back on itself to be truly tight around the Speedlites.


Fig. 3–My stacked Speedlite rig provided a wide field of fill light. I controlled the entire system from the LCD on the back of my camera—via the ST-E3-RT Transmitter in my camera’s hotshoe.

The Bolt Cyclone PP-400DR Dual Outlet Power Pack is the other vital part of my stacked Speedlite rig. This pro-grade, lithium-ion pack cuts my Speedlite recycle time to the bare minimum. With two outlets, I am able to power both Speedlites from a single pack. If your budget is more limited, you could use a Bolt CBP-C1 battery pack and 8 AA batteries on each Speedlite. However, everything on the PP-400DR is more robust, from the size of the power cords to the size of the battery. Regardless of whether you shoot Canon, Nikon, or Sony, there are Bolt cables made for your gear. Additionally, with this cool USB adapter, you can recharge your phone or power a wide range of electronics devices in the field.

Bolt DP PP-400DR Dual Outlet Power Pack

Fig. 4–The Bolt Cyclone PP-400DR runs on a 4500mAh lithium-ion battery and provides external power to two Speedlites. An optional USB adapter allows the battery to be used with a wide range of electronic devices, like cell phones and tablets.


The Look of High-Speed Fill Flash


Fig. 5–The subtle look of fill flash—the photo still looks like it was lit by the sun. The fill flash allows us to see important shadow details (like a sponsor name on the side of a jersey).

 In today’s digital era, it is always worthwhile to ask whether it’s better to light during the shoot or back home on your computer. The right answer, for me, is to light during the shoot.  Fig. 5, above, is lit with fill flash from the stacked Speedlite rig shown above. As you can see, the fill flash blends naturally with the sunlight and allows us to see into the shadows. This shot looks like the sunlight we see on location. Fig. 6, below, is virtually the same shot without any fill flash. By comparison, the natural light-only shot is so contrasty that it looks unnatural.


Fig. 6–Without fill flash the shadows are too dark and the details are lost.

So, can we create the look of fill flash on a computer? I am a huge fan of the Shadows slider in Lightroom. It provides magic when just a bit of additional “light” is needed in the shadows. However, lifting shadows in Lightroom is no replacement for fill flash. As you can see in Fig. 7, below, even pulling the Shadows slider to +100% does not look as natural as the fill flash in Fig. 5—the muscles and clothing lack the definition of the fill flash shot. To my way of thinking, it is always better to light on location so as to maximize the options for fine-tuning the shot in post.


Fig. 7–This is about as good as it gets without fill flash. Here, I reworked Fig. 6 by moving the Shadows slider in Lightroom to +100%. Still, this shot lacks the vibrant lighting that fill flash provides.


Learn These Lighting Techniques

I have two lighting workshops this summer that cover these techniques.

The photos for this article were shot during a lighting demo I did this spring at the Peter Read Miller Sports Photography Workshop in Denver. Peter holds several workshops around the country each year. Check out his site for more information.


8 Responses to Stacking Speedlites For High-Speed Fill Flash

  1. Tim Farrell says:

    I thought the SL’s had to be hard wire synced for the HSS to work. Didn’t think you could use the ST-E3-RT with HSS. Confused.

    • Syl Arena says:

      Tim—I’ve never had issues with HSS working via radio on my 5D Mk II or my 5D Mk III cameras (I know that the manual says otherwise about the 5D Mk II). I’ve used HSS successfully via radio with a 600EX-RT Speedlite as a master and with the ST-E3-RT Transmitter as the master. I’ve no idea why the manual was written the way it was. So, I share your confusion.

  2. Martin Del Vecchio says:

    The Bolt battery unit costs $400 at B&H.

    It is identical to the Godox PB960 unit that Amazon is selling for $204.

    I have four of the Godox units, and they are fantastic. The only problem with them is that they allow you to fire your flash so often that you can easily overheat your flashes.

    • Syl Arena says:

      Martin—Thanks for sharing this info. Overheating is an issue when external battery packs are used. While not widely discussed, one of the new features of the 600EX-RT Speedlite is a much-improved temperature monitor. The 580EX has no sensor and will literally melt. The 580EX II shuts off completely when the sensor is activated by excessive heat. The 600EX-RT has a two-stage heat system that slows the recycling time down when excess heat is monitored. If the heat continues to rise, the the Speedlite shuts itself off completely.

  3. Nicolas says:

    Hi, Syl,
    Just a quick one. With such available light, why not taking the picture with the sun in the back rather than facing the sun with the use of the flash?
    Thanks a lot for sharing, I have learned so much about lighting reading your book/blog.

    • Syl Arena says:

      Nicolas—This is a really great question–why not just swing around and shoot with the sun over my back rather that into it. I’ll give two different answers–one that deals with the geography of the site and one that deals with lighting. In terms of the location, this was a hairpin on a hillside turn that the cyclists skidded around. If I had jumped to the other side of the road, they would have been looking away from the camera. As importantly, the camera would have been shooting into the hillside rather than into the sky. So the rider would get lost against the background. In terms of lighting, it’s important to remember that shape, depth, and texture are all created by shadows. Light shows you the subject. Shadows allow you to see the details–like muscle tone and fabric texture. When the sun is coming in over my back, it hits the subject on both sides of the lens equally–which minimizes the shadows, which makes the image look flat. For really interesting light and shadows in your shots, fire two lights at each other and put your subject in between. Adjust the power of one or both lights until you get the shadows that you want. For this shoot, the two lights were the sun and my Speedlites. Thanks for asking!

  4. Syl,
    Do I take it that you recommend the Bolt battery pack unequivocally for use with the 600ex flashes? The old Canon compact battery flash packs just don’t handle the 600ex well at all. Close to 3 second recharge time when working at plus 1 or more. Total bummer.

    • Syl Arena says:

      I’ve had great success with the Bolt battery packs — both the AA packs and the larger lith-ion units.

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