When purchasing strobes, one of the key considerations that photographers consider is whether the lights have High speed sync (HSS) or not, very few people ever consider the flash duration speed. Flash Duration is the lesser known cousin of HSS. Well we’ve just been getting to know more about it, so hang in there, and let’s learn together. Flash duration is one of the ways that has been used to freeze motion for the longest time. Even the regular flashes use flash duration to freeze motion. Flash duration is the length of time that a strobe/flash takes to emit a single burst of light. This varies across different strobes and even at different flash strengths.
The importance of flash duration or even HSS to the photographer of course all depends on the kind of photography the lights are intended for, some photographers may never use this feature. If you shoot product or scenes with a lot of movement, then the need may arise.
Before we go too far, here are some terms that you will encounter in the article:
Terms
T1– output of a Flash at 10% of its maximum output till when it starts to fade off/dissipate
T5– output of a Flash at 50% of its maximum output till when it starts to fade off/dissipate
HSS –High speed sync
Lights – referring to strobes or flashes
W/S –Watts per second
Studying the Jienbei spark 3 400
So a bit of background on the Jeinbei Spark 3 400; it is a studio light with an out put 0f 400w/s, it has a 15w modelling light and you can control the light from a low of 1 all the way to 10. You can get to know more about it here.
Flash duration speed is denoted by the terms t1 & t5, you can check the meaning up above. When considering the flash duration of a light, the t1 value is more important to note than the t5 as the t1 gives a more accurate representation of the output you will get. However, most manufacturers only give the T5 value of the lights because it is higher. The F stoppers have done a wonderful demonstration to explain these terms and what it all means.
For instance, the Jeinbei Spark 3 400 t5 value is 1/800s-2/2200s so it’s given as a range. I assume this means that when your lights get to 50% & then start to dissipate your output could fall in between these values. Which also means you may not get the same output of light each time, this may also be affected by the power(higher or lower) you have selected. If you think/know this means something else, comment below. After studying these things, we put the Jeinbei Spark 3 400 to the test:
Shot at: shutter -1/250, Aperture- f9, ISO -100. Lens – 85mm. Back lit with one light on an octagon soft box. Power on the lights -1
Get the T1 value of your lights
A suggestion shared by SLR Lounge to roughly get the t1 value of your lights is to divide the t5 value by 3. This would mean that the t1 value of the Jeinbei Spark 3 400 would fall between 1/266-1/666s, which is very low. We wanted to see for ourselves how effective this speed is in freezing motion. If you can, when you are purchasing your lights, make sure the speed of your flash duration is much higher than this.
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Shot at: shutter -1/250, Aperture- f9, ISO -100. Lens – 85mm. Back lit with one light on an octagon soft box. Power on the lights -1
Flash not your shutter freezes motion
One thing that we have just learnt is that when using flash duration, the flash freezes motion and not the shutter speed. So your flash shutter speed may be 1/50 and you may still be able to freeze motion. However, there’s a limitation on the higher side, most DSLRs have a flash sync speed of 1/200 or 1/250 so if you go above this sync speed then you start getting that black edge at the bottom of the image because the shutter opened and closed faster than the input of light coming into the camera. Karl Taylor has broken this down pretty well.
So a faster flash duration is more effective in freezing motion since the flash is the one freezing the motion. If the flash duration speed is slow, then a moving object will be blurry. The other thing to consider is that the higher the flash power, the slower the flash duration and the more blurry the image will be. This is because the output of the light is higher and therefore more energy the light needs to emit hence the drop off/dissipation of the light is much slower, that’s why the recycling time takes longer when the flash is set at a higher output. This is why when using flash duration, a lot of people set the flash power at a much lower output like the lowest power or at least a quarter of the total strength of the light for a faster flash duration.
Shot at: shutter -1/250, Aperture- f11, ISO -500. Lens – 85mm. One topee light(Jeinbei), another jeinbei on the right and a Yongnuo speedlight on the left. Power on the lights -1
In the case of the Jeinbei Spark 3 400 the highest power is 10 and the lowest power is 1. When using flash duration to freeze motion, we have used between the lowest power of 1 and not going beyond a flash strength of 4. We’ve also mostly used a shutter speed of 1/250, a smaller aperture and adjusted the ISO to make sure lighting is good.
Conclusion
Flash duration is very effective in freezing motion, however, the flash duration speed of your lights matters greatly. The flash duration speed of the Jeinbei Spark 3 400 is quite low, so if you will be freezing motion in your professional work, you’re much better of considering another light with a faster flash duration. This version of the Jeinbei can freeze motion but when it gets to some levels like when the items being dropped into a liquid are very heavy, then it doesn’t quite match up.
Shot at: shutter -1/250, Aperture- f11, ISO -500. Lens – 85mm. One topee light(Jeinbei), another jeinbei on the right and a Yongnuo speedlight on the left. Power on the lights -1
Summary
- The faster the flash duration, the more effective it is to freeze motion
- How high the output of your flash is set at, also affects your flash duration
- When using flash duration, it is the flash that freezes the motion and not the speed of the camera.
- Try and find out the t1 value of your lights and so some tests
By no means are we saying we know all there is to know about Flash duration so if you have any suggestions or corrections, share them below.
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