shutter speed

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

 

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!