high speed sync

High Speed Sync vs Neutral Density Filters

HSS vs Neutral Density

I was reading online forums again (yeah, I know...)... I saw a discussion where a photographer was trying to figure out exposure settings for outdoor flash vs ambient light using neutral density filters. He was adamant that he did NOT want to use high speed sync (HSS) because HSS robs the flash of a lot of its power.

This got me thinking... Doesn't using ND filters also rob the flash of power? If you put a 6-stop ND filter over the lens you are effectively lowering the power of the flash 6 stops and also lowering the amount of ambient light 6 stops. If you use high speed sync to raise the shutter speed by six stops you lower the ambient light 6 stops. You also lose power in the flash, about the same 6 stops. Seems pretty much equivalent.


NOTE: Some of the links in this post are affiliate links and I might be compensated if you purchase equipment using the links. But you will also get a discount by using the link or the code CORNICELLO10 on the Interfit Photographic web site. Win/Win situation!


Testing:
So, time to do some testing. Camera is a Canon 5D mkIII with an 85mm f/1.8 lens. All of the photos were made with the white balance set to Daylight. Flash is an Interfit Photographic S1 with high speed sync capabilities modified with a 24-inch collapsible beauty dish. Ambient light meter reading was 1/125 at f/9 and the flash was a bit brighter (f/13). I wanted to make the photographs at f/1.8. 

I needed about 5 and 2/3 stops of neutral density. I had two 0.9 (3-stop) neutral density filters handy, so I stacked them on top of each other and made the first series of photos below with normal sync. Then I removed the filters and switched the Interfit S1 to high speed sync mode and made a similar set of images above the normal sync speed of the camera. The third set as the Interfit S1 in HSS mode plus TTL metering. All the photos were imported into Adobe Lightroom Classic with no adjustments made to them and then I made the following groups via the Print module. The power level on the strobe was not changed between shots in the first two sets of photos. In the third set the strobe was in TTL mode, so it did vary the power (raising it as the shutter speed increased) to maintain the proper exposure.

While this test isn't super scientific, the things I notice are a definite color cast in the photos made with the ND filter, the ND photos do not appear to be quite as sharp as the HSS photos (a complaint I often hear about variable density ND filters, but these were two single density filters), and the ND filters I used required me to take off the lens shade (something I rarely if ever do) to attach them. The ND filters make it more difficult to see through the viewfinder (6 stops more difficult, I don't want to do the math to figure out how many times darker that is). I could/should have bumped the flash power up a third of a stop or so because of the extra density. The background would have remained the same with the subject being a little bit brighter. But it is what it is. All in all a bit of a pain to work with, but it gets the job done if you have a strobe unit that doesn't do HSS.

In the middle set, using the flash in manual exposure mode with high speed sync. Again, I should have/could have bumped up the power of the flash as I went above 1/3200 sec. on the shutter speed. But the last three are still OK and salvageable. 

The set with the S1 in high speed sync mode and TTL exposure seems to be the winner to me. I was able to adjust the shutter speed to make the trees in the background lighter and darker while at the same time keeping the exposure on the subject pretty consistent. I did not make any adjustments on the flash.

Until fairly recently, I hadn't used HSS or TTL all that much with my flashes. I've been a pretty strict manual mode and in the studio type of photographer. Working with the Interfit S1 strobes has changed my mind about this. What are your thoughts about using neutral density filters to balance flash and daylight versus using high speed sync? 

For those interested in how to figure out the exposure using ND filters, here is how I do it.

  • Take a normal meter reading at 1/125 sec. shutter speed (this gives me leeway to raise the shutter speed slightly to darken the background without going over the sync speed of the camera)
  • Example: ISO 100, 1/125 Sec. at f/11
  • Adjust the output of your flash to read the same f/stop (f/11 in this case) or a bit higher WITHOUT THE ND FILTER (I went for f/13 above)
  • Decide on the aperture you want to use for depth of field. In this case I wanted f/1.8
  • Figure that from f/13 to f/1.8 is 5 and 2/3 stops
  • Find a 5 and 2/3 stop neutral density filter or adjust your aperture to match the ND filter(s) you have. If you have a 3 stop filter you can go from f/11 to f/4, with a 4 stop filter you can go to f/2.8, with a 6 stop filter you can go to f/1.4 (I opted for stacking two 3 stop filters above)
  • Take the photo with the ND filter(s) in place
  • Adjust the shutter speed up/down to darken or lighten the background
  • Adjust the power of the flash up/down to get the proper exposure on the subject
  • Deal with focus and color issues

To figure out the exposure with high speed sync

  • Decide on the aperture you want to use
  • Set the camera to that aperture
  • Make sure your flash is in HSS mode
  • Adjust your shutter speed up/down to darken or lighten the background to how you want it to look
  • Adjust the power of the flash to give proper exposure on the subject or use TTL if available

Do note that HSS on speed lights will run through batteries quicker. The folks at Interfit, though, tell me that the S1 battery actually lasts longer in HSS mode. HSS may also shorten the life of the flash tube. But everything is a tradeoff in photography.

Revisiting Shutter Speed In Relation to Flash Photography

How shutter speed affects flash in and out of the studio

Does this ever happen to you?

Does this ever happen to you?

From in-person discussions, q&a sessions in CreativeLive classes I’ve been involved in, and from online discussion groups I have come to the conclusion that shutter speed when using flash is a difficult concept for photographers to grasp when first introduced. We’re all familiar with the three legs of the exposure triangle: ISO (sensitivity), Aperture (amount of light passing through the lens), and Shutter Speed (how long the light is allowed to reach the sensor. For a more in depth look at how shutter speed affects your photos please visit this guide on the PhotographyTalk site). When we add flash into the situation there are another two legs added, the amount of light and the duration of the flash. And at the same time, the Shutter Speed leg’s effect is somewhat tossed away. This makes it sound more complicated than it actually is.

exposure_variables

It is a double exposure
I find that it helps to think of flash photography as making a double exposure with one click of the shutter button. We have an exposure for the existing ambient light that is controlled by the big three (ISO, f/stop, shutter speed). And we have a second simultaneous exposure for the flash that is controlled by ISO, f/stop, and flash power. As ISO and f/stop affect both exposures we can eliminate them from the exposure equation. That leaves us with shutter speed to control the ambient light and flash power to control the flash light. More about that when I talk about working with flash outdoors in sunlight. Let’s start with studio lighting.

In The Studio

What I am saying is that in studio flash photography in the studio the shutter speed doesn’t matter all that much within a certain range, usually around 1/30th of a second to 1/200th of a second. That’s around a 3-stop range. How can that be? What about motion blur at 1/30? 

In the studio we have control over the ambient light situation. We can make the studio completely dark so that even a full 1-second shutter speed at a typical aperture of f/8 or f/11 will not record anything on the sensor. Then we add the flash. The flash provides the powerful light that does record on the sensor. But it only records for that split second that the flash is firing (the flash duration). So out of that 1-second the shutter is opened, the flash is only firing for a fraction of the time. Maybe 1/300 of a second for a big old powerful studio power pack and head system or only 1/9000 of a second for a newer flash unit. The flash duration has effectively replaced the shutter speed in terms of both providing the light for the exposure and for providing the speed necessary to stop motion. Now I am not advocating a shutter speed of 1/30, just using that as an example. Go ahead and test this yourself. Set the ISO and aperture you would be using in the studio (ISO 100 and f/8 is a good starting point) and turn down the ambient light to have a darkened studio. Before connecting and turning on your flash take a photo with those settings to see what gets recorded. In many cases the frame will be black, or show just a faint image. If you see too much image raise your shutter speed to 1/60 and try again.

So why set 1/200 as the other end of the range for studio flash photography? That comes down to how the focal plane shutter in our camera works. With a focal plane shutter (which is what we have in most dSLRs and many mirrorless cameras) there is basically a set of two curtains (simplified, as some have multiple blades, but the effect is the same). When you press the button to take a photograph the first curtain slides out of the way to allow light to reach the sensor. Then the second curtain slides across covering the sensor to end the exposure. To synchronize this with a flash the flash has to fire when neither curtain is covering the sensor. The fastest shutter speed at which there is no curtain in the way is the sync speed for that camera.

Here is an illustration of what happens. On the left we see the first curtain open up to expose the entire sensor in the camera. Then the flash fires, exposing the entire scene. Then the second curtain closes to end the exposure. On the right we see that above the sync speed the first curtain opens, then the second curtain starts to close before the first curtain clears the sensor. Then the flash fires and gets blocked by one of the curtains causing a black band along one edge of the photograph.

Syncronized shutter

Syncronized shutter

Out of sync shutter

Out of sync shutter

Your camera specifications might tell you that the sync speed is 1/180, or 1/200, or even 1/250, so why not go that high with the shutter speed? That number is usually in relation to using a dedicated flash on your camera in the hot shoe. As an example, look at the user manual for the Canon EOS 6D mark II. On page 280 it says:

Non-Canon Flash Units
Sync Speed

The camera can synchronize with non-Canon compact flash units at 1/180 sec. and slower speeds. With large studio flash units, the flash duration is longer than that of a compact flash unit and varies depending on the model. Be sure to check before shooting if flash sync is properly performed by test shooting at a sync speed of approx. 1/60 sec. to 1/30 sec.

Additionally, the use of a remote radio signal flash trigger can add a little bit of a delay to the firing of the flash, requiring a slower shutter speed than expected.

So, what happens if you do set your shutter speed too high? You will notice a dark band along one edge of your photo or no image at all. Here is a set of test images I created with the Canon EOS 6D Mark II and studio strobes (two Interfit Honey Badger flashes, one on the subject and the other on the background). The shutter speed for each photo is shown above the mannequin head. You can clearly see that the flash synced at speeds up to 1/125, but at 1/250 there is the start of a black band along one edge and at 1/2000 the frame is completely black. With some lower cost remote flash triggers you would even see the black band at 1/125, so you would need to set your shutter speed to 1/80 sec. or 1/60. If you have had that black band along the edge of some of your flash photos, here is the explanation.

Studio flash at various shutter speeds

Studio flash at various shutter speeds

High Speed Sync

For some time now dedicated camera flashes (I will refer to them as speed lights here) have offered a feature called High Speed Sync (HSS). This feature is now becoming available in studio flash units like the Interfit S1. It allows the flash unit to synchronize with faster shutter speeds. This comes in most handy when working outdoors in daylight and you want to make photos at wider apertures such as f/2.8 or wider and want to provide some fill light from the flash or even use the flash as your main light source. The issue there is that a typical mid-day exposure at ISO 100 and f/2.8 might call for a shutter speed of 1/2000. As we saw above, the flash won’t have any effect on the image at 1/2000 sec. 

Another situation is where you want to darken the ambient light exposure so that the flash is the main light on the subject. Changing your ISO or aperture will affect the flash exposure as well as the ambient exposure, so your control over the ambient light is your shutter speed. We’ve seen that you are pretty limited in available shutter speeds with normal flash sync. Only being able to speed up to 1/180 or 1/200 doesn’t give you all that much control to darken the ambient light.

Enter HSS
With HSS the flash fires in a stroboscopic fashion (pop, pop, pop, pop, pop) synchronized to the movement of the shutter curtains during the exposure. This happens very quickly, too fast for the human eye to see the multiple flashes, so it still looks like one flash burst. Here is a visual explanation of high speed sync...

On the left there is too much available light to be able to work at f/1.8, everything is overexposed. On the right HSS has been enabled and the shutter speed set to 1/8000 sec. to take the background ambient exposure way down and have the Interfit S1 battery-powered flash provide the main exposure on the subject. Here the S1 is being modified by a 2x3-foot softbox.

On the left there is too much available light to be able to work at f/1.8, everything is overexposed. On the right HSS has been enabled and the shutter speed set to 1/8000 sec. to take the background ambient exposure way down and have the Interfit S1 battery-powered flash provide the main exposure on the subject. Here the S1 is being modified by a 2x3-foot softbox.

Trade-offs
While HSS allows the flash to sync at shutter speeds up to 1/8000 sec., there is a catch. Everything in photography is a trade-off. With HSS the trade-offs are power loss, battery life, and a shorter lifetime for the flash tube. If you have used flash before you are most likely familiar with recycle time. Each time the flash fires it releases energy stored in capacitors. Those capacitors need to charge up again to provide the power for the next flash. Depending on the flash, the time for the recharge can be from  a bit less than 1 second to 8 seconds or more at full power. The time to recycle goes down as the power of the strobe is turned down. Do you see where this is going? In order to have immediate recycle times to allow a number of rapid fire flashes within 1/8000 of a second (as per our example) the power of the flash has to be set way down--you get much less light out of the flash. Right now it seems that most HSS flash units have a maximum power output of around 500 to 600 watt seconds. Anything more powerful would not recycle fast enough or would require larger/heavier power units and be much more expensive. This limits us in that the flash has to be in pretty close to the subject, especially if using big modifiers like soft boxes or umbrellas. Or you end up using smaller/harder light sources and have to deal with the consequences of that. And all that rapid firing of the flash can shorten the lifetime of the flash tube (which is usually a user-replacable item).

Without High Speed Sync you can see the shadow of the shutter curtain when the shutter speed is set higher than the sync speed of the camera

Without High Speed Sync you can see the shadow of the shutter curtain when the shutter speed is set higher than the sync speed of the camera

Do we need High Speed Sync?
It depends.
Yeah, I hate non-commital answers like that. But it does. If you want to totally blur the background on a portrait of one person yes, you might want to make the photo at f/1.4 or f/2.0. And for that you will need to use HSS to be able to work at the high shutter speeds you need in daylight with those apertures. But if you have multiple subjects like a family group you will often be working at f/8 or f/11 or even f/16 to get everyone in focus. At those apertures there is a good chance your shutter speed might drop down to 1/200 or slower and you won’t need HSS.  Even with an individual, if you can pose them someplace where the background is far enough away, you might be able to still get some separation at smaller f/stops and not need HSS. 

For more information about shutter speed in general and how it is used in non-flash photography please refer to this excellent article on the PhotographyTalk website

Thanks for following along! I cover all this and more in my book Anatomy of a Studio Portrait. I also teach lighting classes in the Seattle area at Glazer's Camera and at Photo Center Northwest. Private instruction is also available. Now please go out and light up the world!

John

 

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

 

Enough with the megapixels and ISO!

What I want from the camera manufacturers

I was talking with Jared Platt and Jim Schmelzer after the classes I helped them with at Glazer's Camera's PhotoFest 2017 in Seattle today. After some technical discussions about high speed sync, hypersync, and old ASCOR strobes the conversation turned to camera features. Here are two, no make that three, changes we would like to see in ISO and megapixels. I have no idea if these are practical or feasible, but hey! Let's at least put it out there.

DROP THE ISO!!

The discussion of high speed sync led to our agreement that we don't need any more super high ISO settings. For portraits, especially outside with fill flash, we want LOW ISO settings. ISO 32, ISO 25, and even ISO 10 would be so welcome. Then we could more easily balance daylight exposures with fill flash and have some headroom to adjust shutter speed to control the ambient light levels without having the resort to high speed sync. High speed sync (HSS) is great. But it comes with a price--lower output power. Our lights have to be very close to our subjects with HSS. If we could go to a lower ISO we could keep the lights in regular sync mode and have the power available to back them up out of the frame or to use a larger light modifier with them. Right now the only way to do this with studio power level strobes that don't offer HSS is to use neutral density filters, and that has other complications, like difficulty focusing and dealing with color shifts from ND filters that aren't quite neutral. Are lower ISO settings too much to ask for?

If you aren't familiar with what is sometimes called syncro-sun flash, it is basically using a flash unit to supply fill light on a sunny day to lessen the shadows on your subject. You take an ambient light reading without the flash (let's say that is 1/60 at f/22 at ISO 100) and then you set your flash power to give an appropriate amount of light to open up the shadows. I picked the 1/60 shutter speed so that I have some headroom in case I want to vary the shutter speed to darken the ambient light exposure vs the flash. So, I could go as far as 1/200 to darken the ambient by 1 and 2/3 stops. But I am at f/22 and would much rather be somewhere around f/4 to lessen the depth of field and make the background less distracting. F/22 to f/4 is 5 stops. I could use a 5-stop neutral density filter on the lens to bring down the ambient light level to allow the f/4 aperture. 5 stops is a lot of light being cut out. It is going to give you a very dark viewfinder for composing and focusing. And it might be too dark for autofocus to work.

If, however, ISO 12 was available, the ambient exposure would be 1/60 at f/8 (3 stops different) and then only a 2 stop ND filter would be needed to get the exposure to f/4. Much easier to look through the viewfinder to compose and focus.

Enough with the megapixels!!

How many of us need more than about 20 - 24 megapixels? What if a camera manufacturer took a high megapixel sensor and used some of the pixels to extend dynamic range?

There are lens arrays that let you adjust focus after making the photo (see plenopticsa). And think of the Bayer filter array currently used to create color images. You have a red, a blue, and 2 green pixels that are used to create our color images. What if someone made an array of pixels that, in addition to color, produced an output of a dark, normal, and bright pixels that could be combined to create a kind of high dynamic range image without having to resort to combining multiple images in post processing? All the information would be in one file, so no worry about any movement during the bracketing sequence.

ISO Bracketing

Normally, we would bracket by taking a series of images in quick succession changing the f/stop (which changes the depth of field, which might affect alignment of the multiple images) or by changing the shutter speed (which changes the ability to stop motion, affecting alignment, and which won't work with flash exposures) on each of the images in the bracket. A third bracketing option is to bracket the ISO, but that usually requires additional equipment, like the CamRanger until camera manufacturers get wise to the need for ISO bracketing and add that to their cameras. If the bracketing could be done within one image you wouldn't have to worry about the change in depth of field or about subject movement between images. OK, so that's three things I want from the camera manufacturers, not two.

I haven't upgraded my Canon 5D MkIII or 6D bodies to newer higher megapixel models like the 5D MkIV or 5DSR. I don't need more megapixels. But if a new camera was introduced with better dynamic range and lower ISO settings, I'd be looking hard at purchasing the new model.

How about you? Do you see the benefits of lower ISO (they don't have to remove the higher ISO settings, those can stay, too), better dynamic range, or ISO bracketing? Please comment below.

 

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!