Understanding Flash Duration: Exploring Photography with Mark Wallace


Hi everybody welcome to another episode of Exploring Photography right here on AdoramaTV. I’m Mark Wallace and in today’s episode we’re getting really technical – specifically about flash duration. A flash duration really impacts how motion is frozen in a studio environment, in fact if you do things right a studio strobe will freeze motion much much better than a really fast shutter speed. You can get motion to be frozen in 1/10,000th or 1/20,000th of a second, I mean really crystal BAM clear… However not all studio strobes are created equal, and even if you have a fancy studio strobe not all power settings give you the same flash duration, and so we’re gonna dive into that with some really fancy gear. I’ve got a lab setup here, so we’re gonna do some theoretical stuff, and then we’re going to bring in a fantastic model, and put all this stuff into practical terms, and so you can see how all of the techno mumbo-jumbo translates into real life shooting. So the first thing I need to do, is show you the lab and everything we have setup right here. So let’s do that right now. On the left hand side here I have several different studio strobes from different eras, and different technologies, so I’ve got a Profoto B2, I’ve got a godox, I have a newer Speedotron head, and an older Speedotron, and the Speedotron’s are plugged into this very old pack here, and that way we can compare some newer technologies and some older technologies. We’re going to be firing all four of these heads into a light meter, now this is a very nice light meter. This is a Sekonic 858 D U, and so what this allows me to do is measure the specific time… the duration of the flash, and to record that I’ve got an Osmo Action setup here to record this screen, and I’ve made sure to mount that low enough so that the measurement is not impacted by the little recorder that we’re using to record all of our results. Before we start metering we first need to understand some terms, and how flash duration is measured. So let me put up a little graph here. On one axis I have the power setting of the flash from zero, meaning absolutely nothing, up to ten, which is full power. On the other axis I have the time, so from 0 meaning no time is passed, to the very end, which shows us how much time has passed. Now when a flash fires, the power of the flash goes from 0 very rapidly, up to full power 10. Now some flashes do that really quickly, some flashes sort of just creep up, they’re a little bit slower and then the power decreases from full power all the way down to 0. Now depending on the flash that decrease from full power down to 0 can take shorter amount of time, or a longer amount of time, normally specifications for flash duration is measured with a specification called t5, now that means that it’s the time that the flash is at 50% power or greater, so how long the flash is at half power or more, and so that gives us the T5 value, and that’s what most manufacturers will show you for their flash duration times. However there is a small problem with the T5 value, and that is if you have a very slow flash duration, there’s still a lot of light that’s bumping out of that head, that can still show some motion, so a better measurement of flash duration is called T1. Now what T1 measures, is the power of the flash from 10% and greater, and so as soon as the flash hits 10% all the way to the peak, all the way down to where it falls below, that is considered a true total flash duration, and so what we will be measuring today with our meter is both T5, the manufacturers specification and T1, a more realistic view of what a flash duration is. All right, we’re gonna start doing our measurements. Now I need to introduce you to Sam, this is his studio, and we’re stealing some of his gear, some of his older equipment and your space, thank you so much for letting us do. And he’s gonna be helping me trigger these flashes. So what we’re going to do here is, we’re going to measure the flash duration specifically at the T5 value to begin with, and we’re going to show you a chart that shows each of these different flashes, the ah, how the flash maps out over time and power, and the meter is going to show us a readout of milliseconds, and a fraction of a second, and also it’ll show us our f-stop value. So how bright it is, and how fast it is, in two different ways, and then we’ll also see a graph. It’s really pretty cool, so we’re going to start with our oldest, slowest, technology. This is a Speedotron head, we’re going to start everything at full power to begin with, so tell me when you’re ready Sam, alright, Sam is ready go ahead and fire that – POW… That is a lot of light we can see that this is f/28, that’s a lot of power, but it’s 4.13 milliseconds or 1/200th of a second, 1/250th of a second, so this is not going to be freezing motion. It’s just not a short enough flash duration, we could have a shutter speed much faster than 1/250th of a second, and we can see on the graph here, that the light goes from zero to max really quickly, but then it slowly fades out, and so even our T5 value is slow, but our T1 value would be even slower than that. But let’s keep moving down the line, let’s look at a newer head, and so this is again a Speedotron head, but a newer one I think this is going to flash when we change the head out, okay yep, it turns it off, that flashes, some of the old technology is really fun, so now we’re like using a same power pack, but a newer Speedotron head, remember this is 4.13 milliseconds, let’s look and see what the newer head does, again at full power, so go ahead and fire that, so now we’re looking at 3.14, so it’s a little bit faster, our power outputs about the same f/25, this is really punchy, and if we look at our graph, you can see it’s just a little bit faster to fade out, so our T1 time would be shorter than our T5 time. Here all right, now we’re gonna go down to a Godox, so now we’re into a new modern technology again, at full power and so Sam go ahead, and hit that guy, okay so this is about 1/5 of a second 1.73 milliseconds, at f/18, so not as punchy, but much much quicker, we can look at our graph here, and you can see that it is a much shorter flash duration. It’s much more efficient and now we’re gonna go to a Profoto B2 head, and so again at full power, so go ahead and fire that, and we can see that now we’re at 1/12 thousandth of a second, and so it’s not even a millisecond, so this at f/9, is not as punchy as our Speedotron, but it’s a much shorter flash duration, this is going to freeze motion, you can see here that our duration is much slower. The, the fade-out is a little bit quicker. Now, watch what happens though, look at this graph, you see how this is fading out a little bit slowly, if we take our power all the way down to minimum, so Sam is going to take this down to the very lowest power setting now go ahead and hit that … now this is metering at not even f/1, so you have to be much closer, but look at this, the shutter speed here, or the flash duration, we’re talking 28 thousandth of a second around there, roughly, and then look on this chart here, you can see that that flash is just a spike, and so this is really going to freeze motion, because the light essentially hits the subject and then it’s done, there’s no fade-out, there’s nothing to show any motion, now let’s compare that to our very first flash, so Sam’s gonna change out the head on our Speedotron, we’re gonna use that old head, the very oldest technology, this should be the very worst result, and we’re going to compare this. So remember 1/27,800 of a second is of what our Profoto did, but not very much power so now we’re gonna do this again, go ahead and hit that 1,000th of a second, 1,000th of a second, so it is 27 times slower than our new technology, and you see there is just no spike there, so the point of all of this is your flash, depending on the technology that you’re using and the power settings that you’re using, is going to change the flash duration, they’re not all created equal, and so if you have a flash, and you wanna freeze motion, the key here is no matter which flash are using the lower, the power setting, the shorter the flash duration, the more efficient it’s going to be, and the better your motion is going to be frozen, but to prove that we have a fantastic model, and we’re going to be showing you the differences between different power settings, and how that shows or freezes motion more or less effectively. Before we bring in our model I promised that I would show you the T1 value, so we’re just gonna do the extremes here, so the very first one we’re going to be doing here is, we are going to be metering the Speedotron, so go ahead and fire that Sam. So that fires full power, and this shows 1/69th of a second, that is horrible, and so we’re looking at the entire T1 value, and you can see really a true measurement of the flash duration is horrible it’s 1/16th of a second essentially, it’s not gonna freeze motion, okay let’s pop that down to the lowest power setting, so we can sort of see what that’s going to be doing, so at the lowest setting here, all right it’s all refreshed ready to go. Go ahead and click that, this is showing again at 270th of a second, I can’t say my numbers right, and you can see that again that’s just not efficient, so it’s three, a little over three, and 1/2 milliseconds. That is just not a good it’s not a very high quality flash duration, now we’re gonna look at our Profoto B2 again at full power at T1, go ahead and fire that, that shows us 1/400ths of a second is really a more accurate measurement of the entire flash duration, so that’s still not going to freeze motion the way we want, and so what we’re gonna do here is, go all the way to the lowest power setting, now go ahead and fire that, and that shows us that we’re now at 1/9,000th of a second, that is motion stopping power, and you can look and see it’s because there’s just a spike in that energy, all right now let’s bring out our model, and show you this in real life terms, well now we have Maria here, and she is going to help us demonstrate how this all fits together by jumping across our scene, so come on back here Maria, we have put a little X on the ground here, this is not a fancy lighting setup, we just have our old-fashioned Speedotron here set to about half power, because I need to meter this, which I’m gonna do right now. Now that meters at f/16, which is the smallest aperture opening I have on this lens, so we can’t put this to full power cuz I don’t have f/25 on this lens, and that shows me that the flash duration is about 1/300ths of a second, that is not really really a short flash duration, it’s not motion stopping flash duration, so we’re gonna prove that by having Marina just jump around here, so Maria get ready we’re gonna have you jump across the scene here. I’m all focused up alright ready, 1, 2, 3, go, alright, so when we look at this sort of funny picture, sorry this is not a great lighting setup, we could clearly see that Maria has some blurry hands or feet, or a little bit blurry, this is not frozen motion, so what we’re gonna do next is we’re gonna switch out our Speedotron and we’re going to bring out our B2, we’re gonna see what the same thing looks like using a newer flash with newer technology. Now we’re gonna do the same thing except for now we have a Profoto B2, this is set at 70% power and so we’re shortening our flash durations, so let’s have you go to your spot here. I’m going to meter this really quickly, and this is metering right at f/5.6, and it’s at 3,200th’s of a second, a little bit faster than that actually, and so this is really going to be freezing our motion, so I’m going to hang this really fast right here, and then are you ready to jump around. Ok here we go so on the count of three, ready, uno, dos, tres go, perfect, and so now if we look at this you can clearly see that your hands and then feet and hair everything is frozen, and that is what a short flash duration will do for you. Well thanks Maria for being a good sport and jumping around and be a little bit wacky, but I think that shows us that not all flashes are created equal, some are better at freezing motion because of their shorter flash duration, and even though those can change based on the power output, so the lower the power output this shorter the flash duration, the better you are to be able to freeze motion. Well, thanks for joining us, make sure you follow me on instagram, also I have put a link to Maria’s Instagram in the description of this video. So you can see all of her awesome modelling work. Make sure you click the bell so you get notifications and if you haven’t already, make sure you subscribe to AdoramaTV. It’s free, and we bring you new content almost every single day, well thanks again for joining us, and I will see you again next time.

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