Understanding Flash Duration

Want to freeze movement? Flash duration is key.

Flash duration varies greatly between different types of studio lighting. If you’re looking to freeze movement, it’s important to understand its effects.

Here, Karl Taylor explains exactly what flash duration is and the impact it can have on your shot. In a step-by-step demonstration, he shows different studio lights with different flash durations and their ability to freeze movement.

In this class:

  • Why flash duration is important
  • What impact flash duration has
  • When to use fast flash duration
  • Measuring flash duration
  • Practical demonstrations of different flash durations
  • Sync speed vs flash duration

Questions? Please post them in the comments section below.

Comments

    1. Hi John, speedlites can be extremely fast even 1/30,000th of a second but they are very weak so you need to cluster 4 or 6 of them together to get anything meaningful out of them.

  3. Hi Karl,

    Thinking through High Speed Sync, assuming a slower flash duration which is linear, I guess is it essentially similar to shooting in bright sunlight at high shutter speeds? In bright sunlight the light is there and constant before the shutter opens and after it closes. If a linear flash has a duration longer than the shutter speed then to my thinking it must have much the same properties. Does that make any sense? With a pulsing type HSS that wouldn’t necessarily be the case I guess though.

    I guess that using HSS in an indoor setting with mixed light would also ensure that the ambient/artificial lights won’t taint the image at all?

    1. Hi Kevin yes you are correct for certain High speed sync a longer linear flash duration is used and therefore the amount of light recorded is in this case dependent on your shutter speed.

  4. Hi, good video thanks, you mention that the modelling light would affect the test, I thought the modelling light automatically turned off for the duration of the flash, therefore couldn’t affect the exposure?

  5. ksporry

    I see. Maybe I misunderstood what t0.1 represents, or maybe we’re actually talking about the same thing in different words.
    I found that with my profoto strobes at full power, if the shutterspeed goes beyond a certain speed (in this case 1/400 and faster), the exposure actually drops off. The way I rationalised this for myself was by looking at the t0.1 value at different power settings (published by profoto), and comparing it to my shutter speed, and I found that when my shutter speed was faster than the t0.1 value (or thereabouts), the exposure started to drop off. This was without HSS or HS (I used leaf shutter lenses to achieve the fast shutter speed without losing sync). It sounds like you referred to this phenomenon in your response, but more from a HS or HSS perspective.

    1. Hi Kryn, the t0.1 or t0.5 simply refers to the way the flash burst duration is measured with t0.1 measurement providing you a more accurate interpretation of the whole flash bursts duration and not just a majority percentage of the burst. The issue you were experiencing with faster shutter speeds and full power on strobes is that at full power the burst of light can be so long that your shutter is not syncing as well and/or the burst of light is actually longer than the shutter speed and therefore you lose some light because part of it has been ‘chopped’ off my the shutter.

  6. ksporry

    This is very interesting! I’d love to hear a bit more about flash duration and how it affects exposure. I did some experimenting, and provided a write up in the general chat forum for it. I found it interesting how flash duration could affect exposure depending on shutter speed. Could you explain a bit more on that?

    1. Hi Kryn, in theory on a good flash system it shouldn’t affect exposure in terms of the way I’d expect to use a system. For example if I was using a flash on power 4.5 and then chose to use the high speed flash option then i’d still expect (and with broncolor) would get 4.5 of power, the duration just refers to the brevity of the pulse of flash but not the strength of output. The difference to this would be with HS or HSS (high speed sync modes) where the flash burst is made to last longer (or pulsed) so it can be used at higher shutter speeds (beyond normal sync speeds) such as 1/2000th, 1/4000th, 1/8000th etc, in these cases then yes the shutter speed will have an effect on the flash exposure because the shutter speed itself is either cutting short the flash or extending it depending on the shutter speed selected but this is quite different from true fast t0.1 flash durations. This is why most fast flash durations only operate at mid to low powers on their respective systems.

  7. Hi Karl,
    The first shots with the older light were shot at 1/160. Would it have been possible to shoot at a higher shutter speed to freeze the motion further and open the aperture if required?
    Thanks
    Peter

    1. Hi Peter, you are of course limited by the maximum sync speed of your camera. On most DSLRs this is usually 1/200th or 1/250th and as you open the aperture even one stop then you would need the shutter speed to go from 1/160th to 1/320th to compensate, so you will never have a lot of flexibility this way. There are workarounds with High speed sync that we cover in other chapters but there will be limitations so it is always better to have faster flash duration where possible. Cheers Karl.

  8. Hello Karl, nice and informative session. just a question. will there be difference in freezing power of flash if it is electricity powered or battery powered. Take example if you would have shot this with Siros L?

    Thanks

    1. nope the freezing and power of light will be the same whether you were using a Siros L or a normal Siros if they are both 400 or both 800 joule lights

    1. Hi Tri, then you will likely have a frozen subject from the flash with an after trail image from the ambient light.

  10. I absolutley love how you make everything make sense. I can’t stop spreading the word. You are the perfect teacher. It all just makes sense. Thank you

  11. Very informative as always, thanks Karl. It would be interesting to see how a speed light would compare to those lights. I assume on it’s lowest power it would be somewhere between the two?

    1. Hi Russell, speedlites have very fast flash duration at their low power settings, even speeds of 1/10,000th but the problem is the power is very weak and you need a lot of them to make it work (as you will see in one of my tutorials in the ‘product’ section’) with a studio light you have more useable power and of course attachable modifiers.

  12. Karl you are just the most BRILLIANT instructor out there! The way you explain, the intonation of your voice coupled with your example leave me with NO questions and only inspiration!! MANY THANKS!!

  13. Hello Karl,
    I hope you are well.
    What do you think about the flash duration of the Profoto B1 or D2 to freeze movement ?

    1. Hi Christophe, I’m not up to speed with their specifications, what you need to look for is their specified t0.1 measurements. If they have t0.1 measurements of 1/8000th then they have fast flash durations but then there is also how the flash is cut off and the tail end of light that matters so you would need to refer to tests and actual examples for evidence or rent a unit and try yourself. Cheers Karl.

  14. What is a reasonable t.01 time for freezing humans in motion? As an example, I can freeze football players (American Football) easily with a shutter speed of 1/1000. With that in mind, would a t.01 time of over 1/1000 achieve the same result? Thanks!

    1. Hi Anthony, it is all relative to the amount of movement across the frame. Obviously with a wide angle lens the movement would appear less, whilst in closer it could appear more movement. I find for my liquid shots it has to be t0.1 1/3000th or better on some fashion shots with moving dresses then t0.1 at 1/1000th may be sufficient.

      1. You know, I’ve never thought of freezing power in terms of focal length, but it makes perfect sense now that you mention it. Thanks Karl.

    1. Hi Suliman, flash duration is how long the actual flash lasts and sync is the maximum shutter speed that you can use with a flash. Cameras with leaf shutters can sync faster. It is all explained clearly in the video maybe take another look at it again. There are also some other chapters that will help you. Thanks.

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