flash sync

Hummingbirds in Sequim

Let's try something new!

competing hummingbirds

As previously mentioned, I was out in Sequim, WA last week to teach a lighting workshop. I stayed overnight at a friend’s place and about 15 minutes before we had to drive over to the workshop I decided to try to make a photo of some hummingbirds flying around the deck. I grabbed one of my Interfit Photographic S1 battery operated strobes out of its case along with its standard 7” reflector and a light stand. I set it up about 3 feet from the bird feeder and then popped a Canon EOS M5 camera onto a tripod with the 70-200mm f/4 IS L lens and a cable release. In just a few of minutes I captured some photos and then had to quickly pack up and head to the workshop (more on the workshop coming soon). For these the flash was in manual mode with the power dialed down to its lowest setting (2.0). The S1 uses IGBT technology* to control the flash, so dialing down gives the shortest flash duration to help avoid motion blur. The camera was also in manual mode and the settings were ISO 100, Shutter speed 1/160, and aperture f/6.3

No, these aren’t the best hummingbird photos. If I were to do this again I would give myself more than 15 minutes and would use at least 2, possibly three, lights for more dimensionality. I would also set up a backdrop behind the birds (where the third light might be used). Here the backdrop was a stand of dark trees about 60 yards away that went completely black. For this morning I was mostly interested in seeing if the flash could capture the wings of the hummingbirds and I think they did well. 

In lieu of the mediocre photograph, let’s make this a learning experience.

High Speed Sync?
Some might ask why I used normal sync at 1/160 shutter speed instead of putting the flash into High Speed Sync (HSS) mode. In my experience, HSS is great for matching the flash to the ambient light to photograph at larger apertures (f/4 to f/1.2) to get limited depth of field in an outdoor flash photograph (I didn't need that here, I actually wanted a smaller aperture for more depth of field). But it doesn’t help with freezing motion. Here is a series of photos made with a Canon 430EX II speedlite in normal and HSS modes where you can see what happens to the motion using HSS to photograph a spinning fan.

Notice that at normal sync speeds, even as slow as 1/15 second, the flash duration is fast enough to freeze the motion of the spinning fan blades. As long as the room is dark enough, the ambient light won't affect the photo and the short flash duration becomes your effective "shutter speed" even if the shutter is open for a full second or more. When you get into the HSS zone there is a lot of blur, even though the shutter speeds are faster.

How Flash and Shutter Speed Sync

If you are not familiar with High Speed Sync, what it does is pulses the flash rapidly during the exposure to enable it to synchronize with the moving blades of your camera’s shutter. In normal sync mode you press the shutter button, the first curtain of the shutter opens, the flash fires, then the second (rear) curtain closes. When you go above your camera sync speed (which could be anywhere from 1/60 to 1/250 second) the first curtain opens, the second curtain starts to close, then the flash fires.

With the shutter speed set at or below the sync speed

Shutter speed is set higher than the sync speed

flash sync black band

If you are just a step or two above your sync speed you get a dark band across one edge of your photo. At higher speeds the flash doesn’t register at all, as the second curtain starts closing as soon and fast as the first curtain opens. 

High Speed Sync fires a series of lower powered flashes in perfect synchronization with the moving curtains so that the image looks like it was made with one flash.

How flash and shutter speed sync with each other. Click on the image to view it larger.

Downsides to High Speed Sync

The series of flashes, while being great for letting you photograph at wide open apertures, does have some downsides. The most noticeable is the reduction in power output. Normally the strobe fires and needs a second or two for the capacitors to recycle and be ready to fire again. In HSS the flash doesn’t have any time for recycling, so it puts out a series of very low powered flashes. The light usually has to be close to your subject. You will lose a stop of power every time you double the shutter speed above the sync speed. The second downside is that it doesn’t help much with freezing action. Third is that it goes through batteries quicker. And fourth is that over time the rapid flashing can lead to a lower life expectancy of the flash tube. A note on that, though, is that I have some studio flash units here that are close to or even more than 40 years old and the flash tubes are still working on them (but they’ve never been used for HSS, which didn’t exist 40 years ago). 

*IGBT = Insulated Gate Bipolar Transistor
Different flash technologies go about controlling power output and flash duration differently. Large studio pack and head systems usually control power by switching banks of capacitors on or off (capacitor switching). Lowering the power on the pack will shorten the flash duration.
Until recently, most monoblock strobes would vary the voltage of the capacitors (voltage lowering) to control power. In these lowering the power leads to longer flash duration with some change in the color temperature of the light.
IGBT units have constant voltage, but have the ability to shut off the flash tube (tail trimming) when the desired amount of light has been emitted. Here flash duration gets faster as the power is decreased. Color temperature should be a little more consistent at different power levels and by cutting off the tail of the flash the ability to freeze motion is increased. When using IGBT flashes, going to half power or lower gives the faster flash durations. 

DISCLOSURE: I am part of the Interfit CreativePros Team

 

More shutter speed and speed lights

Speed lights

Thanks for all the feedback on yesterday's shutter speed post here and on social media. Some folks wondered about the action stopping capabilities of the speed light. I only have one speed light to test with, a Canon 430 EXii. So here are some more photos of the fan.

First, I will start out with this series of photos taken with no flash. Here only the shutter speed of the camera is affecting the amount of motion blur in the fan blades. Shutter speeds range from 1/8 second to 1/1000 second using window light.

No flash, just window light at the indicated shutter speeds

No flash, just window light at the indicated shutter speeds

The next series was taken with the flash on Manual power control and the camera shutter set to 1/15th second. The first image is without flash to show the ambient light at 1/15 second at f/8. The images then progress from 1/64 power to full power. The f/stop was adjusted for each frame to give the same exposure.

flash-15th-second

This next series is the same as the above, except that the shutter speed was increased to 1/125 second. I want you to notice that most of the images look exactly the same, despite the three step difference in shutter speed. Where you will see a difference is in the low powered shots where the aperture had to be opened up to compensate for the low power flash, causing more ambient light to be recorded at 1/15th than at 1/125th. But the edges of the blades are still about the same, despite the ghosting.

flash-125-second

Here are close-ups of the fan blades at 1/4 power on the flash. On the left is 1/15 second at f/11 and on the right is 1/125 second at f/11. The motion blur is the same. The flash duration is the effective shutter speed in the studio. The flash doesn't care how long the shutter is open, and the flash isn't affected by how long the shutter is open (as long as the shutter speed is at or below the sync speed). If the room was completely dark the camera shutter could be set to 30 seconds or more and the exposure would still be the same as at 1/125. The only light hitting the fan is the brief flash from the speed light.

15-vs-125.jpg

One more series of photo and then I hope we're done with the fan and can get back to more creative endeavors. This time the flash is in eTTL mode at a range of shutter speeds. The aperture is the same (f/5.6) in the 6 flash lit shots, the output of the speed light is controlled by the eTTL circuitry. The seventh image is the fan at 1/2000 second with no flash for comparison.

ettl-flash

One of the things to notice in this series is that at 1/15 and 1/125 (the first two images) the flash is in normal mode and the speed of the flash freezes the blades. Above 1/200 second the flash is in high-speed sync mode where the flash fires a series of flashes (too quick in succession for the eye to see) as the shutter curtains move across the sensor. Because of the rapid movement of the fan blades, they are in different positions for each of the flashes and the fan blades show more motion at the faster shutter speeds (1/250, 1/500, 1/1000 second). At 1/2000 second the shutter speed alone stops the blades, as you can see by comparing the last two images, both taken at 1/2000 second. One is with the and one is without the flash.

As pointed out by Paul in the comments on yesterday's post, most subjects probably won't be moving as fast as the fan is, so you might not get a lot of subject motion blur using high-speed sync. I am exaggerating the effect here to make the point that high-speed sync is a tool used to help balance outdoor exposures between flash and sunlight while maintaining large apertures for shallow depth of field. It isn't meant to help stop subject motion, and, as can be seen here, may actually show more motion in extreme conditions.

Shutter Speed with Flash or Strobes

Avoiding Motion Blur

In response to some questions in the comments section about power settings and freezing motion with a speed light I added a new post to the blog today.

Yesterday I got a question from a friend on Facebook asking how to get their flash to sync with their camera at a shutter speed higher than 1/125 so they could freeze the motion of their subject (children in this case). This question also comes up in almost every CreativeLive strobe lighting class that I've worked on. I hope that this post can help clear up the big misconceptions about shutter speed and flash photography.

Instead of using children, I decided on something that moves even faster--a box fan.

In the first series of images below we see 6 images of the fan. The first one (1) was  taken without a flash. The rest were taken with different brands and models of studio strobes. And the most important thing to recognize here is that all 6 images were taken at 1/15 of a second, and the fan was running at the same speed in all the images. What I hope to show you here is that in the studio with strobes the shutter speed is pretty much irrelevant as long as it isn't so slow that ambient light infiltrates the exposure or isn't too fast that the camera's shutter cannot synchronize with the flash, which will leave a black band across one side of the image (see my previous post on sync speed for more information on that).

shutter-speed-strobe-motion

As noted above, photo 1 was taken at 1/15th second with no flash
#2 was with a Speedotron 805 pack and a model 102 head (1/670 second flash duration)
#3 was with the same Speedotron 805 pack, but with a model 202 head (1/900 second flash duration)
#4 was taken with an SPS Systems Excalibur 1600 monolight (unknown flash duration)
#5 was taken with a Speedotron Force 5 monolight (1/1500 second flash duration)
#6 was taken with a Paul C. Buff Einstein monolight in Action mode (1/4826 second flash duration, and yes, the fan was spinning)

studio-shutter-speed-strobe

In the above series of images, the shutter speeds in both rows go from 1/15 to 1/30 to 1/60, and finally 1/125 (all at f/7.1). In the top row the studio strobe was not turned on, so you can see the base exposure. There is a slight rendering of the subject in the 1/15 and even the 1/30 second shots, but not enough to affect the exposure when the strobe is turned on (second row). At 1/60 and 1/125 there is no ambient light at all in the exposure. All of the images in the bottom row show the same exposure, controlled by the ISO, flash power, and aperture. The shutter speed is inconsequential to the overall exposure in a reasonably dark studio setting.

What about speedlights? What about high-speed sync and speed lights? Let's look at another set of images. As above, #1 is the same reference image as used above at 1/15 second with no flash.

flash-sync-speedlight-shutter-speed-blur

#2 was taken with a Canon 430EXii flash at 1/15 second
#3 was taken with a Canon 430EXii flash in high-speed sync mode at 1/500 second

Here you can see that engaging high-speed sync does not help stop subject motion. It actually led to more subject motion, even though the shutter speed was at 1/500 second. Additionally, high-speed sync robs the flash of power, leading to an underexposed image. This is because high-speed sync works by pulsing the flash multiple times at a lower power during the exposure. This makes the speed light less bright, helps burn through batteries, and does not help stop motion blur.

I hope that this helps clarify why shutter speed is usually not an important factor in determining exposure or in stopping motion when working in a studio with speedlights or strobes. The important factor here is the flash duration of your strobes or speed lights.


Taking it outside

Shutter speed with flash does play an important role in outdoor flash photography with a lot of ambient light. There your ISO and aperture control the exposure on the flash-lit subject and the shutter speed affects the brightness of the background. By slowing down your shutter speed in this situation you will make the background brighter. By speeding it up, you darken the background.

This situation (outdoor flash photography) is where high-speed sync (HSS) comes into play. Without HSS you are limited to shutter speeds at or below the camera's sync speed. Depending on the camera, this could typically be anywhere from 1/60 to 1/250. You will need to consult the owner's manual for your particular camera to find the sync speed.

The usual situation here is that you want to take a flash photo outdoors on a sunny day and want to use a large aperture (maybe 2.8 or faster) to blur out the background. The base exposure, without flash in this situation might be something like 1/5000 second at f/2.0. If you add a flash that doesn't have HSS your shutter speed is limited to, in this example, 1/160 second. This means that you cannot shoot at f/2.0, you need to stop down to f/11. But this gives you too much depth of field (the background objects are too in focus and distracting). By engaging HSS on your speed light you can now sync the camera at 1/2000, but your flash will need to be in close to your subject because of the reduction in output power that enables HSS.

fill-flash-no-high-speed-sync

The image on the left above is at 1/160 second at f/11 with no flash
The middle image is 1/160 at f/11 with flash
In both images, the background is too distracting. To fix that, we want to shoot at f/2.0
The image on the right is 1/5000 at f/2.0 with no flash to give shallow depth of field. But the eyes are in shadow. We would like to use a flash to fill in the shadows.

fill-flash-high-speed-sync

Here we start with the last image from the last series. 1/5000 at f/2.0 with no flash
In the middle image I turned on the flash without high-speed sync which dropped the shutter speed to 1/200 second (maximum sync speed on the Canon 5D mkIII). Because I am at f/2.0 for the background, the image is way overexposed.

On the right I turned on high-speed sync which let the camera and speedlight sync at 1/5000 second at f/2.0. Now there is some light in the eyes, shadows are opened up a bit, and the background is nicely blurred to help make the subject stand out.

Controlling the ambient exposure

Earlier I mentioned controlling the ambient exposure via shutter speed. Let's take a look at that. Here I have combined high speed sync, manual exposure, and manual flash settings.

The base setting for the sky exposure is 1/2000 at f/4. My on-camera flash is set to full power so that it has enough reach for high-speed sync. The images above are shot at 1/640, 1/1000, 1/2000, and 1/4000 with flash. Notice that the background is lighter in the first two images, normal in the third, and darker in the last image. The last image, at 1/4000 shows a darker subject because the flash didn't have enough power to handle high-speed sync even at full power at this distance and at such a high shutter speed.

Questions? Comments? Thanks for following along!