Will flash freeze movement at slow shutter speeds?
Does flash freeze motion at slow shutter speeds (in low light)? The answer is … maybe. Perhaps. It depends. There are several factors which will determine whether flash will freeze motion at slow shutter speeds.
It is difficult giving a definitive answer because it depends on the scenario. In short – if your subject isn’t lit by much available light (with ambient light 4 stops or less than your flash exposure), then flash will freeze the action … if there is no bright background. Probably. But it depends on the type of movement, and how critical you are about image sharpness.
See? We just can’t quite get away from those qualifiers – perhaps / depends / probably. But let’s jump into this and see when flash will freeze the action, and when you’re likely to be successful.
The photo above, of Oktavia dancing, was shot at 1/10 @ f/2.8 @ 1600 ISO
At 1/10th of a second, the flash did freeze her movement.
You can see the background lights streak as I moved my hand-held camera to try and keep up with her movements. I was trying to hide the flash behind her, but I liked the effect here. You can also see the city lights streak through her arm as she moved.
Let’s quickly look at the pull-back shot to see how the flashes were set up, and then we continue the discussion on whether flash freezes action …
The lighting setup for this photo shoot
We were on the boardwalk area at the Ice Cream Factory in Brooklyn, with its magnificent view of Manhattan’s lights. Therefore my exposure was based on the city lights. With test shots, it looked like 1/10 @ f/2.8 @ 1600 ISO would let enough lights register.
Erik wanted to shoot with his brand-new Fuji X-T1 (Amazon) here, so we decided to use old-school PocketWizards with manual off-camera flashes. This meant there was no infra-red beam from the camera / flash to help with focus. We were working in complete darkness there! I So I had Erik (who helped me on the shoot), hold up a video light (right hand) for me, so I could focus. Oktavia would be statically standing so I could focus on her. Then I would tell Erik to drop the video light completely out of shot, and then I’d cue Oktavia to start her dance movements. I would rapidly fire my camera, since it was tough to see in the dark what her actual movements were.
Flash exposure – we worked via the distance scale on the Nikon SB-910 Speedlight (Amazon). It would tell me what distance the flash should be from my subject for a specific distance / ISO combination. This is explained thoroughly in this article – getting the most power from your flash / speedlite / speedlight – although in a completely different context. This time we wanted very little light from our flashes, because we were shooting at 1600 ISO and f/2.8
The main flash on Oktavia was gelled with 1/2 CTS but the flash behind her wasn’t gelled. Then by changing the WB on my camera to be correct for the main (gelled) flash, the background went blue. That gave a nice rim-light on her with the difference in color. This technique of gelling one flash to get a blue background, is thoroughly explained in that linked article.
- Nikon D4
- Nikon 70-200mm f2.8 AF-S VR II /equivalent Canon EF 70-200mm f/2.8L IS II
- Nikon SB-910 Speedlight /equivalent Canon 600EX-RT Speedlite
Direction & Quality of Light
I wanted to distill the essence of what we, as photographers, work with – light! Before we can truly grasp on-camera flash and off-camera flash, and really, any kind of photography, we have to be aware of the direction and quality of light. We need to observe the light that we have, and then decide how best to use it, or enhance it.
With this book, I try my best to share those “aha!” moments with you, and I do believe this book can make a difference to your photography.
The book is available on Amazon USA and Amazon UK, or can be ordered through Barnes & Nobles and other bookstores. The book is also available on the Apple iBook Store, as well as Amazon Kindle.
Will flash freeze the action?
Let’s step through different aspects and see how the flash & ambient combination works:
a.) Flash duration
Without getting into a thorough discussion of T.5 and T.1 durations of flashes, let’s look at flash duration in a more simple way:
Studio flashes generally control the amplitude of the flash pulse to control power / brightness. Therefore at lower power settings, the flash duration becomes longer. Some studio flashes have durations as low as the vicinity of 1/500 which isn’t enough to freeze fast action.
Speedlights control power / brightness by shortening the duration of the flash pulse. Therefore, the lower the flash power setting, the shorter (i.e., faster) the flash pulse. So if you want to freeze drops splashing, then you’re most likely going to use speedlights at low power settings.
For simplicity of explanation, let’s say that the flash duration is in the order of 1/1000 and this would then imply that normal human motion would be frozen by flash. But if you were photographing sports action in the studio, then a high-kick from a martial artist would still not have hands and feet crisply sharp. So you’d have to accept that minor compromise, or delve much deeper into fast-duration flash.
b.) Ambient exposure
Inevitably, when we use flash, we have to consider the ambient light. Especially here. Whether the ambient light is bright or whether we are working in low light, will have impact on whether flash could freeze action.
- bright ambient light:
For this scenario, use a faster shutter speed and high-speed flash to freeze the action.
- low ambient light:
If you are working in typical on-location scenarios, and your ambient is only 2 stops under – which would be typical for using off-camera flash for on-location portraits, then the flash won’t be enough to freeze the action … because you would have to rely on your camera’s actual shutter speed to freeze action.
This then is the crux of the matter for portrait photographers shooting on location in low light:
– how low is the ambient light?
– what is your shutter speed?
If the ambient light is 1 or 2 stops under, and your shutter speed is slow, then flash will NOT “freeze the action”. Or, you will have to be okay with ambient smearing of your subject. That can be cool too. But it isn’t “freezing the movement” then.
With the ambient light around 3 or 4 stops under, you have a better fighting chance of the ambient light not obviously smearing.
If your ambient exposure is 5 stops under your main flash exposure, then the ambient will not register. So then you’re safe. Working in near darkness with a dark background, and only using flash.
c.) The brightness of your background
Now, lets say you work in the dark, and flash will freeze the action because so little ambient light will register. Now you have to consider how bright the background is. If the background is, for example, a bright sunset, then your subject will “disappear” into the brighter light as they move. Hands and limbs could disappear or “melt” into the background.
You can see a little bit of that happening with Oktavia’s wrist which blends with the city lights as she moved. So with a uniformly brighter background (like a sunset), the hand and arm would’ve “melted” into the background.
So that is something to keep in mind as well – even with your subject in deep shadow, how bright is the background? Enough to show blur? The flash would freeze the movement, but the ambient exposure with the very slow shutter speed, would still show because of the brighter background.
Summary
Will flash freeze the action? It depends.
With this photo session of Oktavia, I knew I would have a greater chance of success because I worked within what was reasonably possible. The ambient light was very low – the background was bright to the point that it would be a problem. In other words, pick your battles. Not everything will work every time, so you have to sway the photo shoot’s success in your favor.
Hopefully this article will help explain what to consider and which situations are going to be more successful than others. In the end though, you have to do some homework and play. Shoot a lot, and see. That’s always very good philosophy in photography – practice a lot!
Related articles
- Off-camera flash in low light – choosing your shutter speed (model: Molly K)
- Shutter speed choice with flash
- Dragging the shutter
- So what are your camera settings? – the thought-process
- Flash photography tutorial
Neil, I suspect a typo here: “Therefore at lower power settings, the flash duration becomes longer.” Should that not read “becomes shorter”?
Nope, it is (generally) correct there as stated.
You need to consider the T.5 and T.1 durations of the pulse, as the amplitude becomes lower.
I was assuming you were referring to speedlights. As jean bernier says below:
Speedlights: It is the reverse of typical monolights: as you power down, you get shorter duration.
As I had it: “Speedlights control power / brightness by shortening the duration of the flash pulse.”
Hi Neil,
Your articles on OCF are inspiring and a superb teaching aid.
I do have a question if I may?
I quote from one of your articles on OCF
If you are working in typical on-location scenarios, and your ambient is only 2 stops under – which would be typical for using off-camera flash for on-location portraits, then the flash won’t be enough to freeze the action … because you would have to rely on your camera’s actual shutter speed to freeze action.
If my ambient, after reducing it by 2 stops was 1/30 at f2 at ISO100 then I understand that this shutter speed would not stop any normal “subject movement” – camera shake would not be a problem due to Sonys image stabilisation even at 1/30. Its subject movement that concern me only.
Is the answer to raise my ISO to say 400, resulting in a shutter speed of 1/125 which should stop normal subject movement? minor head movement etc on a reasonably static model or would 1/250 be safer? I understand that more excessive subject movement requires faster shutter speeds for the ambient light exposure.
Sorry for the long message but it’s important that I understand, thank you in anticipation.
Hi there
1/125th should be good for normal small movements like someone moving their head slightly if they stand still. For actual movement like dance, it would be too slow. You will get motion blur then.
1/250th would always be safer than 1/125th to reduce motion blur.
The 1/30th that you mention – that will only be “safe” for shorter lenses. The moment you try to handle a 70-200mm, it most likely will be too slow a shutter speed to handhold with predictably sharp results.
Awesome article Neil!! I did this a few times and could not understand all of the parameters that needs to be considered to be more effective with this type of shooting. I appreciate how you laid it out the methods, what parameters matter, but you left us with the rest to do and learn!! Keep it coming!
To make sure I am understanding you, the gist is:
To freeze motion with flash (when using lower shutter speeds, where one would normally expect motion blur to be an issue), I first need your correct ambient exposure to be more than 2 full stops less that my correct subject / flash exposure. 4 stops has been ideal in the example given.
I then need to be aware that a background with lots of bright patches – which would be close to equal to or greater than the correct exposure of my subject (and thus not the required >2stops) – can mean I wouldn’t freeze motion occurring over those patches. To keep the subject clean I would need to ensure that their bodies do not intersect with brighter patches of light in the background
If I want to freeze motion where the correct background / ambient exposure is <2 stops under the subject, I should instead employ HSS flash and the higher shutter speed that would be needed to correct expose for ambient.
Despite the above, its not an exact science, and things like the kind of flash I am using will affect how well this works… Is this a correct rough understanding?
And I assume – I need to be in manual flash. No ETTL for this?
Or could I just pump my FEC up to compensate for the difference between correct ambient and subject exposures (assuming my FEC went up that many stops)?
If you bump up your FEC when you already have correct flash exposure, it will simply over-expose.
And yes, you most surely can use TTL for this type of scenario. Manual vs TTL flash has nothing to do with whether or not flash will freeze action.
That’s too simplistic. You will only use HSS if the shutter speed warrants it … and that is in bright light. And that has no direct correlation to “the ambient being 2 stops under.”
With this entire tutorial article, you also have to keep in mind how much movement you have — a sports portrait vs a couple dancing. You have to keep in mind whether the movement is towards or away from you, vs lateral from you.
There are a LOT of factors kicking in, and this article illustrates that you can’t just assume that “flash will freeze the action”.
Ahh k – got it now. Had a brain freeze re: TTL – obviously my flash just needs to meter off my subject to get the right exposure, for some reason I was thinking it would try and expose for the background.
Got some practicin’ to do. Thanks!
Flash duration is of paramount importance when shooting “extreme action”, the likes of golf swings, dancers jumping, etc.
To clear up the confusion, it goes like this AFAIK:
Mono light: typically 1/600th at full pwr, easily down to 1/300th at minimum output. Specs are most of the time
t= 5, for ALL styles of flash, a misleading measure that is useful for those marketeers. Voltage charge of the capacitors is the regulating parameter. Lower voltage: it takes longer to dissipate the energy in the tube.
Speedlights: It is the reverse of typical monolights: as you power down, you get shorter duration.
Typically 1/600th at full pwr (manual), down to 1/20000th at minimum pwr. The pulse is abruptly terminated by a thyristor at ALL OTHER SETTINGS than full pwr. With TTL, you have no idea what the power setting is, so the pulse duration will be anywhere between max and min…. The Einstein by Buff uses this circuitry, and it is basically a large manual speedlight.
Traditional power packs: banks of capacitors are in or out of the circuit. It is the total capacitance in use that determines the power output and the flash duration. The lower the setting, (the smaller the capacitance) the shorter the flash duration. Yes, it is the reverse of typical monolights. I’ve seen durations as long as 1/200th on some models. Speedotrons I’ve used for years past were between 1/300th at full ( 2400ws) and 1/600th at min ( 400ws)… dial down controls that appeared on more recent models do lengthen the flash duration when used…
Hope this helps.
thank you!
In the instance where the background exposure is relatively bright (e.g. as per the city lights in your above shot of Octavia dancing) and the subject is exposed entirely by flash – then is there an advantage to use rear curtain sync?
Am I correct in assuming that with rear curtain sync, so long as the subject exposure is slightly brighter than the background lights then the subject image will effectively “paint over” the already recorded image of the lights and thus effectively eliminate the “ghosting” effect (as seen on Octavia’s right forearm) and therefore more effectively “freeze the subject of the image?
Rear curtain sync wouldn’t have much (or any) impact here, since there is no ambient light on her.
The streaking is from how her arms move “through” the buildings in the background, not because of ambient light on her smearing.
2.8 lens. Just out of interest what focus point on the camera did/do you use?
Always focused on her face. Since she moves and might move out of position, we did lose some frames due to the photos then being mis-focused.
Mixing ambient light and flash is something that I’ve been wrestling with this summer. The weather was hot an humid, so I went looking for ways to shoot active subjects (macro photographer). I hate black backgrounds due to flash falloff, and those are easy to avoid when working with lethargic subjects and flash only (example: . But when shooting active subjects in the field I don’t sometimes don’t have the luxury of using a staged background and have to rely on the ambient light. So I’ve tried to walk the shutter with my ISO set to 200 and the Fstop at 11 and keep the magnification at 2x or less. I’ve had some successes (https://www.flickr.com/photos/dalantech/20161887583/in/dateposted-public/) but I’ve also ran into a problem with capturing motion, and more frequently it shows up like a shadow (check out the antenna at the top of the frame: . I’ve been trying to keep the ambient under exposed by two stops, but I think sometimes I’m getting too close to the natural light exposure. Also using rear (second) curtain sync to help freeze motion just in case I do record some movement. Any tips you could give me would be greatly appreciated! I know that using HSS won’t work -it’s like taking multiple exposures with the flash, and for macro I’d rather have the stopping power of a single pulse.
That photo of the insect where you get to see the shadow of ambient light vs flash – there is camera shake that comes into play there, because it isn’t just the insect which has that shadow.
You say that HSS won’t work … I think you should try it. It behaves differently than you seem to expect.
Hello Neil,
Many thanks for the article, I’m struggling to understand if a flash will freeze a portrait of someone in a living room situation, where you are trying to balance the ambient light (say a lamp) and using a strobe. if you were using a slow shutter speed to capture the lamp, say at 1/30th of a second, but then you use a flash to light your main subject – a person on the chair. And this is all shot on a tripod, I assume you would end up with a sharp subject? And the ambient shutter would be ok because used on a tripod?
Again, it depends on how under-exposed your subject is by the ambient light. When the ambient is 4 stops or less, UNDER the flash exposure, then you’re not likely to see any camera shake or subject movement. The flash will freeze that.
When your flash and ambient are within 3 stops of one another in exposure, and you’re using a slow shutter speed, then a tripod would be handy.
Thank you; this is quite helpful. I also work with dancers. For the dancer’s safety, there has to be some ambient light. My approach would be to set the camera for the exposure that I would use with flash, then shoot with the flash turned off; that should tell me how bad the ambient light “ghosting” would be when the flash is used. My guess is that for me, in the studio situations in which I usually work, shutter speed will continue to be an important factor in freezing motion. That’s why I got into medium format in the first place–to use a faster shutter without flash sync problems.
Hi Neil
If my studio was free of ambient light, what flash duration do you think would be needed to totally freeze a a jumping person or dog for example?
My flashes can give me about 2500s (t1 time) and wondering if this will be quick enough? I will experiment next week but interested to hear you thoughts.
Cheers
Duncs
Yeah — this is something you’d have to experiment with, because it will depend entirely on how fast they are moving.
I would think that 1/2,500 should be fast enough to freeze most movement from an animal or human.